Draft ECMA-262 / March 19, 2025
ECMAScript® 2025 Language Specification
About this Specification
The document at https://tc39.es/ecma262/ is the most accurate and up-to-date ECMAScript specification. It contains the content of the most recent yearly snapshot plus any finished proposals (those that have reached Stage 4 in the proposal process and thus are implemented in several implementations and will be in the next practical revision) since that snapshot was taken.
This document is available as a single page and as multiple pages.
Contributing to this Specification
This specification is developed on GitHub with the help of the ECMAScript community. There are a number of ways to contribute to the development of this specification:
- GitHub Repository: https://github.com/tc39/ecma262
- Issues: All Issues, File a New Issue
- Pull Requests: All Pull Requests, Create a New Pull Request
- Test Suite: Test262
- Editors:
-
Community:
- Discourse: https://es.discourse.group/
- Chat: Matrix
- Mailing
List Archives: https://esdiscuss.org/
Refer to the
Introduction
This Ecma Standard defines the ECMAScript 2025 Language. It is the sixteenth edition of the ECMAScript Language Specification. Since publication of the first edition in 1997, ECMAScript has grown to be one of the world's most widely used general-purpose programming languages. It is best known as the language embedded in web browsers but has also been widely adopted for server and embedded applications.
ECMAScript is based on several originating technologies, the most well-known being JavaScript (Netscape) and JScript (Microsoft). The language was invented by Brendan Eich at Netscape and first appeared in that company's Navigator 2.0 browser. It has appeared in all subsequent browsers from Netscape and in all browsers from Microsoft starting with Internet Explorer 3.0.
The development of the ECMAScript Language Specification started in November 1996. The first edition of this Ecma Standard was adopted by the Ecma General Assembly of June 1997.
That Ecma Standard was submitted to ISO/IEC JTC 1 for adoption under the fast-track procedure, and approved as international standard ISO/IEC 16262, in April 1998. The Ecma General Assembly of June 1998 approved the second edition of ECMA-262 to keep it fully aligned with ISO/IEC 16262. Changes between the first and the second edition are editorial in nature.
The third edition of the Standard introduced powerful regular expressions, better string handling, new control statements, try/catch exception handling, tighter definition of errors, formatting for numeric output and minor changes in anticipation of future language growth. The third edition of the ECMAScript standard was adopted by the Ecma General Assembly of December 1999 and published as ISO/IEC 16262:2002 in June 2002.
After publication of the third edition, ECMAScript achieved massive adoption in conjunction with the World Wide Web where it has become the programming language that is supported by essentially all web browsers. Significant work was done to develop a fourth edition of ECMAScript. However, that work was not completed and not published as the fourth edition of ECMAScript but some of it was incorporated into the development of the sixth edition.
The fifth edition of ECMAScript (published as ECMA-262 5th edition) codified de facto interpretations of the language specification that have become common among browser implementations and added support for new features that had emerged since the publication of the third edition. Such features include
The fifth edition was submitted to ISO/IEC JTC 1 for adoption under the fast-track procedure, and approved as international standard ISO/IEC 16262:2011. Edition 5.1 of the ECMAScript Standard incorporated minor corrections and is the same text as ISO/IEC 16262:2011. The 5.1 Edition was adopted by the Ecma General Assembly of June 2011.
Focused development of the sixth edition started in 2009, as the fifth edition was being prepared for publication. However, this was preceded by significant experimentation and language enhancement design efforts dating to the publication of the third edition in 1999. In a very real sense, the completion of the sixth edition is the culmination of a fifteen year effort. The goals for this edition included providing better support for large applications, library creation, and for use of ECMAScript as a compilation target for other languages. Some of its major enhancements included modules, class declarations, lexical block scoping,
ECMAScript 2016 was the first ECMAScript edition released under Ecma TC39's new yearly release cadence and open development process. A plain-text source document was built from the ECMAScript 2015 source document to serve as the base for further development entirely on GitHub. Over the year of this standard's development, hundreds of pull requests and issues were filed representing thousands of bug fixes, editorial fixes and other improvements. Additionally, numerous software tools were developed to aid in this effort including Ecmarkup, Ecmarkdown, and Grammarkdown. ES2016 also included support for a new exponentiation operator and adds a new method to Array.prototype called includes.
ECMAScript 2017 introduced Async Functions, Shared Memory, and Atomics along with smaller language and library enhancements, bug fixes, and editorial updates. Async functions improve the asynchronous programming experience by providing syntax for promise-returning functions. Shared Memory and Atomics introduce a new Object.values, Object.entries, and Object.getOwnPropertyDescriptors.
ECMAScript 2018 introduced support for asynchronous iteration via the dotAll flag, named capture groups, Unicode property escapes, and look-behind assertions. Lastly it included object rest and spread properties.
ECMAScript 2019 introduced a few new built-in functions: flat and flatMap on Array.prototype for flattening arrays, Object.fromEntries for directly turning the return value of Object.entries into a new Object, and trimStart and trimEnd on String.prototype as better-named alternatives to the widely implemented but non-standard String.prototype.trimLeft and trimRight built-ins. In addition, it included a few minor updates to syntax and semantics. Updated syntax included optional catch binding parameters and allowing U+2028 (LINE SEPARATOR) and U+2029 (PARAGRAPH SEPARATOR) in string literals to align with JSON. Other updates included requiring that Array.prototype.sort be a stable sort, requiring that JSON.stringify return well-formed UTF-8 regardless of input, and clarifying Function.prototype.toString by requiring that it either return the corresponding original source text or a standard placeholder.
ECMAScript 2020, the 11th edition, introduced the matchAll method for Strings, to produce an import(), a syntax to asynchronously import Modules with a dynamic specifier; BigInt, a new number primitive for working with arbitrary precision Promise.allSettled, a new Promise combinator that does not short-circuit; globalThis, a universal way to access the global this value; dedicated export * as ns from 'module' syntax for use within modules; increased standardization of for-in enumeration order; import.meta, a
ECMAScript 2021, the 12th edition, introduced the replaceAll method for Strings; Promise.any, a Promise combinator that short-circuits when an input value is fulfilled; AggregateError, a new Error type to represent multiple errors at once; logical assignment operators (??=, &&=, ||=); WeakRef, for referring to a target object without preserving it from garbage collection, and FinalizationRegistry, to manage registration and unregistration of cleanup operations performed when target objects are garbage collected; separators for numeric literals (1_000); and Array.prototype.sort was made more precise, reducing the amount of cases that result in an
ECMAScript 2022, the 13th edition, introduced top-level await, allowing the #x in obj syntax, to test for presence of private fields on objects; regular expression match indices via the /d flag, which provides start and end indices for matched substrings; the cause property on Error objects, which can be used to record a causation chain in errors; the at method for Strings, Arrays, and Object.hasOwn, a convenient alternative to Object.prototype.hasOwnProperty.
ECMAScript 2023, the 14th edition, introduced the toSorted, toReversed, with, findLast, and findLastIndex methods on Array.prototype and TypedArray.prototype, as well as the toSpliced method on Array.prototype; added support for #! comments at the beginning of files to better facilitate executable ECMAScript files; and allowed the use of most Symbols as keys in weak collections.
ECMAScript 2024, the 15th edition, added facilities for resizing and transferring ArrayBuffers and SharedArrayBuffers; added a new RegExp /v flag for creating RegExps with more advanced features for working with sets of strings; and introduced the Promise.withResolvers convenience method for constructing Promises, the Object.groupBy and Map.groupBy methods for aggregating data, the Atomics.waitAsync method for asynchronously waiting for a change to shared memory, and the String.prototype.isWellFormed and String.prototype.toWellFormed methods for checking and ensuring that strings contain only well-formed Unicode.
Dozens of individuals representing many organizations have made very significant contributions within Ecma TC39 to the development of this edition and to the prior editions. In addition, a vibrant community has emerged supporting TC39's ECMAScript efforts. This community has reviewed numerous drafts, filed thousands of bug reports, performed implementation experiments, contributed test suites, and educated the world-wide developer community about ECMAScript. Unfortunately, it is impossible to identify and acknowledge every person and organization who has contributed to this effort.
Allen Wirfs-Brock
ECMA-262, Project Editor, 6th Edition
Brian Terlson
ECMA-262, Project Editor, 7th through 10th Editions
Jordan Harband
ECMA-262, Project Editor, 10th through 12th Editions
Shu-yu Guo
ECMA-262, Project Editor, 12th through 15th Editions
Michael Ficarra
ECMA-262, Project Editor, 12th through 15th Editions
Kevin Gibbons
ECMA-262, Project Editor, 12th through 15th Editions
1 Scope
This Standard defines the ECMAScript 2025 general-purpose programming language.
2 Conformance
A conforming implementation of ECMAScript must provide and support all the types, values, objects, properties, functions, and program syntax and semantics described in this specification.
A conforming implementation of ECMAScript must interpret source text input in conformance with the latest version of the Unicode Standard and ISO/IEC 10646.
A conforming implementation of ECMAScript that provides an application programming interface (API) that supports programs that need to adapt to the linguistic and cultural conventions used by different human languages and countries must implement the interface defined by the most recent edition of ECMA-402 that is compatible with this specification.
A conforming implementation of ECMAScript may provide additional types, values, objects, properties, and functions beyond those described in this specification. In particular, a conforming implementation of ECMAScript may provide properties not described in this specification, and values for those properties, for objects that are described in this specification.
A conforming implementation of ECMAScript may support program and regular expression syntax not described in this specification. In particular, a conforming implementation of ECMAScript may support program syntax that makes use of any “future
A conforming implementation of ECMAScript must not implement any extension that is listed as a Forbidden Extension in subclause
A conforming implementation of ECMAScript must not redefine any facilities that are not
A conforming implementation of ECMAScript may choose to implement or not implement Normative Optional subclauses. If any Normative Optional behaviour is implemented, all of the behaviour in the containing Normative Optional clause must be implemented. A Normative Optional clause is denoted in this specification with the words "Normative Optional" in a coloured box, as shown below.
2.1 Example Normative Optional Clause Heading
Example clause contents.
A conforming implementation of ECMAScript must implement Legacy subclauses, unless they are also marked as Normative Optional. All of the language features and behaviours specified within Legacy subclauses have one or more undesirable characteristics. However, their continued usage in existing applications prevents their removal from this specification. These features are not considered part of the core ECMAScript language. Programmers should not use or assume the existence of these features and behaviours when writing new ECMAScript code.
2.2 Example Legacy Clause Heading
Example clause contents.
2.3 Example Legacy Normative Optional Clause Heading
Example clause contents.
3 Normative References
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
The Unicode Standard.
https://unicode.org/versions/latest
ISO/IEC 10646, Information Technology — Universal Multiple-Octet Coded Character Set (UCS) plus Amendment 1:2005, Amendment 2:2006, Amendment 3:2008, Amendment 4:2008, and additional amendments and corrigenda, or successor.
ECMA-402, ECMAScript Internationalization API Specification, specifically the annual edition corresponding to this edition of this specification.
https://www.ecma-international.org/publications-and-standards/standards/ecma-402/
ECMA-404, The JSON Data Interchange Format.
https://www.ecma-international.org/publications-and-standards/standards/ecma-404/
4 Overview
This section contains a non-normative overview of the ECMAScript language.
ECMAScript is an object-oriented programming language for performing computations and manipulating computational objects within a
ECMAScript was originally designed to be used as a scripting language, but has become widely used as a general-purpose programming language. A scripting language is a programming language that is used to manipulate, customize, and automate the facilities of an existing system. In such systems, useful functionality is already available through a user interface, and the scripting language is a mechanism for exposing that functionality to program control. In this way, the existing system is said to provide a
ECMAScript was originally designed to be a Web scripting language, providing a mechanism to enliven Web pages in browsers and to perform server computation as part of a Web-based client-server architecture. ECMAScript is now used to provide core scripting capabilities for a variety of
ECMAScript usage has moved beyond simple scripting and it is now used for the full spectrum of programming tasks in many different environments and scales. As the usage of ECMAScript has expanded, so have the features and facilities it provides. ECMAScript is now a fully featured general-purpose programming language.
4.1 Web Scripting
A web browser provides an ECMAScript
A web server provides a different
Each Web browser and server that supports ECMAScript supplies its own
4.2 Hosts and Implementations
To aid integrating ECMAScript into
An implementation is an external source that further defines facilities enumerated in Annex
An implementation-defined facility is one that defers its definition to an external source without further qualification. This specification does not make any recommendations for particular behaviours, and conforming implementations are free to choose any behaviour within the constraints put forth by this specification.
An implementation-approximated facility is one that defers its definition to an external source while recommending an ideal behaviour. While conforming implementations are free to choose any behaviour within the constraints put forth by this specification, they are encouraged to strive to approximate the ideal. Some mathematical operations, such as Math.exp
A host is an external source that further defines facilities listed in Annex
A host hook is an abstract operation that is defined in whole or in part by an external source. All
- It must return either a
normal completion or athrow completion .
A host-defined facility is one that defers its definition to an external source without further qualification and is listed in Annex
A host environment is a particular choice of definition for all
This specification follows the editorial convention of always using the most specific term. For example, if a facility is
Both
4.3 ECMAScript Overview
The following is an informal overview of ECMAScript—not all parts of the language are described. This overview is not part of the standard proper.
ECMAScript is object-based: basic language and
ECMAScript defines a collection of built-in objects that round out the definition of ECMAScript entities. These built-in objects include the Object, Function, Boolean, Symbol, and various Error objects; objects that represent and manipulate numeric values including Math, Number, and Date; the text processing objects String and RegExp; objects that are indexed collections of values including Array and nine different kinds of Typed Arrays whose elements all have a specific numeric data representation; keyed collections including Map and Set objects; objects supporting structured data including the JSON object, ArrayBuffer, SharedArrayBuffer, and DataView; objects supporting control abstractions including generator functions and Promise objects; and reflection objects including Proxy and Reflect.
ECMAScript also defines a set of built-in operators. ECMAScript operators include various unary operations, multiplicative operators, additive operators, bitwise shift operators, relational operators, equality operators, binary bitwise operators, binary logical operators, assignment operators, and the comma operator.
Large ECMAScript programs are supported by modules which allow a program to be divided into multiple sequences of statements and declarations. Each module explicitly identifies declarations it uses that need to be provided by other modules and which of its declarations are available for use by other modules.
ECMAScript syntax intentionally resembles Java syntax. ECMAScript syntax is relaxed to enable it to serve as an easy-to-use scripting language. For example, a variable is not required to have its type declared nor are types associated with properties, and defined functions are not required to have their declarations appear textually before calls to them.
4.3.1 Objects
Even though ECMAScript includes syntax for class definitions, ECMAScript objects are not fundamentally class-based such as those in C++, Smalltalk, or Java. Instead objects may be created in various ways including via a literal notation or via new Date(2009, 11) creates a new Date object. Invoking a Date() produces a string representation of the current date and time rather than an object.
Every object created by a
In a class-based object-oriented language, in general, state is carried by instances, methods are carried by classes, and inheritance is only of structure and behaviour. In ECMAScript, the state and methods are carried by objects, while structure, behaviour, and state are all inherited.
All objects that do not directly contain a particular property that their prototype contains share that property and its value. Figure 1 illustrates this:
CF is a new expressions: cf1, cf2, cf3, cf4, and cf5. Each of these objects contains properties named
Unlike most class-based object languages, properties can be added to objects dynamically by assigning values to them. That is,
Although ECMAScript objects are not inherently class-based, it is often convenient to define class-like abstractions based upon a common pattern of
4.3.2 The Strict Variant of ECMAScript
The ECMAScript Language recognizes the possibility that some users of the language may wish to restrict their usage of some features available in the language. They might do so in the interests of security, to avoid what they consider to be error-prone features, to get enhanced error checking, or for other reasons of their choosing. In support of this possibility, ECMAScript defines a strict variant of the language. The strict variant of the language excludes some specific syntactic and semantic features of the regular ECMAScript language and modifies the detailed semantics of some features. The strict variant also specifies additional error conditions that must be reported by throwing error exceptions in situations that are not specified as errors by the non-strict form of the language.
The strict variant of ECMAScript is commonly referred to as the strict mode of the language. Strict mode selection and use of the strict mode syntax and semantics of ECMAScript is explicitly made at the level of individual
In order to conform to this specification, an ECMAScript implementation must implement both the full unrestricted ECMAScript language and the strict variant of the ECMAScript language as defined by this specification. In addition, an implementation must support the combination of unrestricted and strict mode source text units into a single composite program.
4.4 Terms and Definitions
For the purposes of this document, the following terms and definitions apply.
4.4.1 implementation-approximated
an
4.4.2 implementation-defined
an
4.4.3 host-defined
same as
Editorially, see clause
4.4.4 type
set of data values as defined in clause
4.4.5 primitive value
member of one of the types Undefined, Null, Boolean, Number, BigInt, Symbol, or String as defined in clause
A primitive value is a datum that is represented directly at the lowest level of the language implementation.
4.4.6 object
member of the type Object
An object is a collection of properties and has a single prototype object. The prototype may be
4.4.7 constructor
The value of a
4.4.8 prototype
object that provides shared properties for other objects
When a constructor.prototype, and properties added to an object's prototype are shared, through inheritance, by all objects sharing the prototype. Alternatively, a new object may be created with an explicitly specified prototype by using the Object.create built-in function.
4.4.9 ordinary object
object that has the default behaviour for the essential internal methods that must be supported by all objects
4.4.10 exotic object
object that does not have the default behaviour for one or more of the essential internal methods
Any object that is not an
4.4.11 standard object
object whose semantics are defined by this specification
4.4.12 built-in object
object specified and supplied by an ECMAScript implementation
Standard built-in objects are defined in this specification. An ECMAScript implementation may specify and supply additional kinds of built-in objects.
4.4.13 undefined value
primitive value used when a variable has not been assigned a value
4.4.14 Undefined type
type whose sole value is the
4.4.15 null value
primitive value that represents the intentional absence of any object value
4.4.16 Null type
type whose sole value is the
4.4.17 Boolean value
member of the
There are only two Boolean values,
4.4.18 Boolean type
type consisting of the primitive values
4.4.19 Boolean object
member of the
A Boolean object is created by using the Boolean new expression, supplying a Boolean value as an argument. The resulting object has an internal slot whose value is the Boolean value. A Boolean object can be coerced to a Boolean value.
4.4.20 String value
primitive value that is a
A String value is a member of the
4.4.21 String type
set of all possible String values
4.4.22 String object
member of the
A String object is created by using the String new expression, supplying a String value as an argument. The resulting object has an internal slot whose value is the String value. A String object can be coerced to a String value by calling the String
4.4.23 Number value
primitive value corresponding to a double-precision 64-bit binary format
A Number value is a member of the
4.4.24 Number type
set of all possible Number values including
4.4.25 Number object
member of the
A Number object is created by using the Number new expression, supplying a Number value as an argument. The resulting object has an internal slot whose value is the Number value. A Number object can be coerced to a Number value by calling the Number
4.4.26 Infinity
Number value that is the positive infinite Number value
4.4.27 NaN
Number value that is an
4.4.28 BigInt value
primitive value corresponding to an arbitrary-precision
4.4.29 BigInt type
set of all possible BigInt values
4.4.30 BigInt object
member of the
4.4.31 Symbol value
primitive value that represents a unique, non-String Object
4.4.32 Symbol type
set of all possible Symbol values
4.4.33 Symbol object
member of the
4.4.34 function
member of the
In addition to its properties, a function contains executable code and state that determine how it behaves when invoked. A function's code may or may not be written in ECMAScript.
4.4.35 built-in function
built-in object that is a function
Examples of built-in functions include parseInt and Math.exp. A
4.4.36 built-in constructor
built-in function that is a
Examples of built-in Object and Function. A
4.4.37 property
part of an object that associates a key (either a String value or a Symbol value) and a value
Depending upon the form of the property the value may be represented either directly as a data value (a primitive value, an object, or a
4.4.38 method
function that is the value of a property
When a function is called as a method of an object, the object is passed to the function as its
4.4.39 built-in method
method that is a built-in function
Standard built-in methods are defined in this specification. A
4.4.40 attribute
internal value that defines some characteristic of a property
4.4.41 own property
property that is directly contained by its object
4.4.42 inherited property
property of an object that is not an own property but is a property (either own or inherited) of the object's prototype
4.5 Organization of This Specification
The remainder of this specification is organized as follows:
Clause
Clauses
Clauses
Clauses
Clause
5 Notational Conventions
5.1 Syntactic and Lexical Grammars
5.1.1 Context-Free Grammars
A context-free grammar consists of a number of productions. Each production has an abstract symbol called a nonterminal as its left-hand side, and a sequence of zero or more nonterminal and terminal symbols as its right-hand side. For each grammar, the terminal symbols are drawn from a specified alphabet.
A chain production is a production that has exactly one nonterminal symbol on its right-hand side along with zero or more terminal symbols.
Starting from a sentence consisting of a single distinguished nonterminal, called the goal symbol, a given context-free grammar specifies a language, namely, the (perhaps infinite) set of possible sequences of terminal symbols that can result from repeatedly replacing any nonterminal in the sequence with a right-hand side of a production for which the nonterminal is the left-hand side.
5.1.2 The Lexical and RegExp Grammars
A lexical grammar for ECMAScript is given in clause
Input elements other than white space and comments form the terminal symbols for the syntactic grammar for ECMAScript and are called ECMAScript tokens. These tokens are the /*…*/ regardless of whether it spans more than one line) is likewise simply discarded if it contains no line terminator; but if a
A RegExp grammar for ECMAScript is given in
Productions of the lexical and RegExp grammars are distinguished by having two colons “::” as separating punctuation. The lexical and RegExp grammars share some productions.
5.1.3 The Numeric String Grammar
A numeric string grammar appears in
Productions of the numeric string grammar are distinguished by having three colons “:::” as punctuation, and are never used for parsing source text.
5.1.4 The Syntactic Grammar
The syntactic grammar for ECMAScript is given in clauses
When a stream of code points is to be parsed as an ECMAScript
When a parse is successful, it constructs a parse tree, a rooted tree structure in which each node is a Parse Node. Each Parse Node is an instance of a symbol in the grammar; it represents a span of the source text that can be derived from that symbol. The root node of the parse tree, representing the whole of the source text, is an instance of the parse's
New Parse Nodes are instantiated for each invocation of the parser and never reused between parses even of identical source text. Parse Nodes are considered the same Parse Node if and only if they represent the same span of source text, are instances of the same grammar symbol, and resulted from the same parser invocation.
Parsing the same String multiple times will lead to different Parse Nodes. For example, consider:
let str = "1 + 1;";
eval(str);
eval(str);Each call to eval converts the value of str into
Productions of the syntactic grammar are distinguished by having just one colon “:” as punctuation.
The syntactic grammar as presented in clauses
In certain cases, in order to avoid ambiguities, the syntactic grammar uses generalized productions that permit token sequences that do not form a valid ECMAScript
- The sequence of tokens originally matched by P is parsed again using N as the
goal symbol . If N takes grammatical parameters, then they are set to the same values used when P was originally parsed. - If the sequence of tokens can be parsed as a single instance of N, with no tokens left over, then:
- We refer to that instance of N (a Parse Node, unique for a given P) as "the N that is covered by P".
- All Early Error rules for N and its derived productions also apply to the N that is covered by P.
- Otherwise (if the parse fails), it is an early Syntax Error.
5.1.5 Grammar Notation
5.1.5.1 Terminal Symbols
In the ECMAScript grammars, some terminal symbols are shown in fixed-width font. These are to appear in a source text exactly as written. All terminal symbol code points specified in this way are to be understood as the appropriate Unicode code points from the Basic Latin block, as opposed to any similar-looking code points from other Unicode ranges. A code point in a terminal symbol cannot be expressed by a \
In grammars whose terminal symbols are individual Unicode code points (i.e., the lexical, RegExp, and numeric string grammars), a contiguous run of multiple fixed-width code points appearing in a production is a simple shorthand for the same sequence of code points, written as standalone terminal symbols.
For example, the production:
is a shorthand for:
In contrast, in the syntactic grammar, a contiguous run of fixed-width code points is a single terminal symbol.
Terminal symbols come in two other forms:
- In the lexical and RegExp grammars, Unicode code points without a conventional printed representation are instead shown in the form "<ABBREV>" where "ABBREV" is a mnemonic for the code point or set of code points. These forms are defined in
Unicode Format-Control Characters ,White Space , andLine Terminators . - In the syntactic grammar, certain terminal symbols (e.g.
IdentifierName andRegularExpressionLiteral ) are shown in italics, as they refer to the nonterminals of the same name in the lexical grammar.
5.1.5.2 Nonterminal Symbols and Productions
Nonterminal symbols are shown in italic type. The definition of a nonterminal (also called a “production”) is introduced by the name of the nonterminal being defined followed by one or more colons. (The number of colons indicates to which grammar the production belongs.) One or more alternative right-hand sides for the nonterminal then follow on succeeding lines. For example, the syntactic definition:
states that the nonterminal while, followed by a left parenthesis token, followed by an
states that an
5.1.5.3 Optional Symbols
The subscripted suffix “opt”, which may appear after a terminal or nonterminal, indicates an optional symbol. The alternative containing the optional symbol actually specifies two right-hand sides, one that omits the optional element and one that includes it. This means that:
is a convenient abbreviation for:
and that:
is a convenient abbreviation for:
which in turn is an abbreviation for:
so, in this example, the nonterminal
5.1.5.4 Grammatical Parameters
A production may be parameterized by a subscripted annotation of the form “[parameters]”, which may appear as a suffix to the nonterminal symbol defined by the production. “parameters” may be either a single name or a comma separated list of names. A parameterized production is shorthand for a set of productions defining all combinations of the parameter names, preceded by an underscore, appended to the parameterized nonterminal symbol. This means that:
is a convenient abbreviation for:
and that:
is an abbreviation for:
Multiple parameters produce a combinatoric number of productions, not all of which are necessarily referenced in a complete grammar.
References to nonterminals on the right-hand side of a production can also be parameterized. For example:
is equivalent to saying:
and:
is equivalent to:
A nonterminal reference may have both a parameter list and an “opt” suffix. For example:
is an abbreviation for:
Prefixing a parameter name with “?” on a right-hand side nonterminal reference makes that parameter value dependent upon the occurrence of the parameter name on the reference to the current production's left-hand side symbol. For example:
is an abbreviation for:
If a right-hand side alternative is prefixed with “[+parameter]” that alternative is only available if the named parameter was used in referencing the production's nonterminal symbol. If a right-hand side alternative is prefixed with “[~parameter]” that alternative is only available if the named parameter was not used in referencing the production's nonterminal symbol. This means that:
is an abbreviation for:
and that:
is an abbreviation for:
5.1.5.5 one of
When the words “one of” follow the colon(s) in a grammar definition, they signify that each of the terminal symbols on the following line or lines is an alternative definition. For example, the lexical grammar for ECMAScript contains the production:
which is merely a convenient abbreviation for:
5.1.5.6 [empty]
If the phrase “[empty]” appears as the right-hand side of a production, it indicates that the production's right-hand side contains no terminals or nonterminals.
5.1.5.7 Lookahead Restrictions
If the phrase “[lookahead = seq]” appears in the right-hand side of a production, it indicates that the production may only be used if the token sequence seq is a prefix of the immediately following input token sequence. Similarly, “[lookahead ∈ set]”, where set is a
These conditions may be negated. “[lookahead ≠ seq]” indicates that the containing production may only be used if seq is not a prefix of the immediately following input token sequence, and “[lookahead ∉ set]” indicates that the production may only be used if no element of set is a prefix of the immediately following token sequence.
As an example, given the definitions:
the definition:
matches either the letter n followed by one or more decimal digits the first of which is even, or a decimal digit not followed by another decimal digit.
Note that when these phrases are used in the syntactic grammar, it may not be possible to unambiguously identify the immediately following token sequence because determining later tokens requires knowing which lexical
5.1.5.8 [no LineTerminator here]
If the phrase “[no
indicates that the production may not be used if a throw token and the
Unless the presence of a
5.1.5.9 but not
The right-hand side of a production may specify that certain expansions are not permitted by using the phrase “but not” and then indicating the expansions to be excluded. For example, the production:
means that the nonterminal
5.1.5.10 Descriptive Phrases
Finally, a few nonterminal symbols are described by a descriptive phrase in sans-serif type in cases where it would be impractical to list all the alternatives:
5.2 Algorithm Conventions
The specification often uses a numbered list to specify steps in an algorithm. These algorithms are used to precisely specify the required semantics of ECMAScript language constructs. The algorithms are not intended to imply the use of any specific implementation technique. In practice, there may be more efficient algorithms available to implement a given feature.
Algorithms may be explicitly parameterized with an ordered, comma-separated sequence of alias names which may be used within the algorithm steps to reference the argument passed in that position. Optional parameters are denoted with surrounding brackets ([ , name ]) and are no different from required parameters within algorithm steps. A rest parameter may appear at the end of a parameter list, denoted with leading ellipsis (, ...name). The rest parameter captures all of the arguments provided following the required and optional parameters into a
Algorithm steps may be subdivided into sequential substeps. Substeps are indented and may themselves be further divided into indented substeps. Outline numbering conventions are used to identify substeps with the first level of substeps labelled with lowercase alphabetic characters and the second level of substeps labelled with lowercase roman numerals. If more than three levels are required these rules repeat with the fourth level using numeric labels. For example:
- Top-level step
- Substep.
- Substep.
- Subsubstep.
- Subsubsubstep
- Subsubsubsubstep
- Subsubsubsubsubstep
- Subsubsubsubstep
- Subsubsubstep
- Subsubstep.
A step or substep may be written as an “if” predicate that conditions its substeps. In this case, the substeps are only applied if the predicate is true. If a step or substep begins with the word “else”, it is a predicate that is the negation of the preceding “if” predicate step at the same level.
A step may specify the iterative application of its substeps.
A step that begins with “Assert:” asserts an invariant condition of its algorithm. Such assertions are used to make explicit algorithmic invariants that would otherwise be implicit. Such assertions add no additional semantic requirements and hence need not be checked by an implementation. They are used simply to clarify algorithms.
Algorithm steps may declare named aliases for any value using the form “Let x be someValue”. These aliases are reference-like in that both x and someValue refer to the same underlying data and modifications to either are visible to both. Algorithm steps that want to avoid this reference-like behaviour should explicitly make a copy of the right-hand side: “Let x be a copy of someValue” creates a shallow copy of someValue.
Once declared, an alias may be referenced in any subsequent steps and must not be referenced from steps prior to the alias's declaration. Aliases may be modified using the form “Set x to someOtherValue”.
5.2.1 Abstract Operations
In order to facilitate their use in multiple parts of this specification, some algorithms, called abstract operations, are named and written in parameterized functional form so that they may be referenced by name from within other algorithms. Abstract operations are typically referenced using a functional application style such as OperationName(arg1, arg2). Some abstract operations are treated as polymorphically dispatched methods of class-like specification abstractions. Such method-like abstract operations are typically referenced using a method application style such as someValue.OperationName(arg1, arg2).
5.2.2 Syntax-Directed Operations
A syntax-directed operation is a named operation whose definition consists of algorithms, each of which is associated with one or more productions from one of the ECMAScript grammars. A production that has multiple alternative definitions will typically have a distinct algorithm for each alternative. When an algorithm is associated with a grammar production, it may reference the terminal and nonterminal symbols of the production alternative as if they were parameters of the algorithm. When used in this manner, nonterminal symbols refer to the actual alternative definition that is matched when parsing the source text. The source text matched by a grammar production or
When an algorithm is associated with a production alternative, the alternative is typically shown without any “[ ]” grammar annotations. Such annotations should only affect the syntactic recognition of the alternative and have no effect on the associated semantics for the alternative.
Syntax-directed operations are invoked with a parse node and, optionally, other parameters by using the conventions on steps
- Let status be SyntaxDirectedOperation of
SomeNonTerminal . - Let someParseNode be the parse of some source text.
- Perform SyntaxDirectedOperation of someParseNode.
- Perform SyntaxDirectedOperation of someParseNode with argument
"value" .
Unless explicitly specified otherwise, all
but the
Runtime Semantics:
- Return
Evaluation ofStatementList .
5.2.3 Runtime Semantics
Algorithms which specify semantics that must be called at runtime are called runtime semantics. Runtime semantics are defined by
5.2.3.1 Completion ( completionRecord )
The abstract operation Completion takes argument completionRecord (a
Assert : completionRecord is aCompletion Record .- Return completionRecord.
5.2.3.2 Throw an Exception
Algorithms steps that say to throw an exception, such as
- Throw a
TypeError exception.
mean the same things as:
- Return
ThrowCompletion (a newly createdTypeError object).
5.2.3.3 ReturnIfAbrupt
Algorithms steps that say or are otherwise equivalent to:
ReturnIfAbrupt (argument).
mean the same thing as:
Assert : argument is aCompletion Record .- If argument is an
abrupt completion , returnCompletion (argument). - Else, set argument to argument.[[Value]].
Algorithms steps that say or are otherwise equivalent to:
ReturnIfAbrupt (AbstractOperation()).
mean the same thing as:
- Let hygienicTemp be AbstractOperation().
Assert : hygienicTemp is aCompletion Record .- If hygienicTemp is an
abrupt completion , returnCompletion (hygienicTemp). - Else, set hygienicTemp to hygienicTemp.[[Value]].
Where hygienicTemp is ephemeral and visible only in the steps pertaining to ReturnIfAbrupt.
Algorithms steps that say or are otherwise equivalent to:
- Let result be AbstractOperation(
ReturnIfAbrupt (argument)).
mean the same thing as:
Assert : argument is aCompletion Record .- If argument is an
abrupt completion , returnCompletion (argument). - Else, set argument to argument.[[Value]].
- Let result be AbstractOperation(argument).
5.2.3.4 ReturnIfAbrupt Shorthands
Invocations of ? indicate that
- ? OperationName().
is equivalent to the following step:
ReturnIfAbrupt (OperationName()).
Similarly, for method application style, the step:
- ? someValue.OperationName().
is equivalent to:
ReturnIfAbrupt (someValue.OperationName()).
Similarly, prefix ! is used to indicate that the following invocation of an abstract or
- Let val be ! OperationName().
is equivalent to the following steps:
- Let val be OperationName().
Assert : val is anormal completion .- Set val to val.[[Value]].
! or ? before the invocation of the operation:
- Perform ! SyntaxDirectedOperation of
NonTerminal .
5.2.3.5 Implicit Normal Completion
In algorithms within
- when the result of applying
Completion ,NormalCompletion ,ThrowCompletion , orReturnCompletion is directly returned - when the result of constructing a
Completion Record is directly returned
It is an editorial error if a
- Return
true .
means the same things as any of
- Return
NormalCompletion (true ).
or
- Let completion be
NormalCompletion (true ). - Return
Completion (completion).
or
- Return
Completion Record { [[Type]]:normal , [[Value]]:true , [[Target]]:empty }.
Note that, through the
- Return ? completion.
The following example would be an editorial error because a
- Let completion be
NormalCompletion (true ). - Return completion.
5.2.4 Static Semantics
Context-free grammars are not sufficiently powerful to express all the rules that define whether a stream of input elements form a valid ECMAScript
Static Semantic Rules have names and typically are defined using an algorithm. Named Static Semantic Rules are associated with grammar productions and a production that has multiple alternative definitions will typically have for each alternative a distinct algorithm for each applicable named static semantic rule.
A special kind of static semantic rule is an Early Error Rule.
5.2.5 Mathematical Operations
This specification makes reference to these kinds of numeric values:
- Mathematical values: Arbitrary real numbers, used as the default numeric type.
- Extended mathematical values:
Mathematical values together with +∞ and -∞. - Numbers:
IEEE 754-2019 binary64 (double-precision floating point) values. - BigInts:
ECMAScript language values representing arbitraryintegers in a one-to-one correspondence.
In the language of this specification, numerical values are distinguished among different numeric kinds using subscript suffixes. The subscript 𝔽 refers to Numbers, and the subscript ℤ refers to BigInts. Numeric values without a subscript suffix refer to
In general, when this specification refers to a numerical value, such as in the phrase, "the length of y" or "the
When the term integer is used in this specification, it refers to a
Numeric operators such as +, ×, =, and ≥ refer to those operations as determined by the type of the operands. When applied to
Conversions between
The mathematical function
The mathematical function
The notation “
The phrase "the result of clamping x between lower and upper" (where x is an
The mathematical function
The mathematical function
Mathematical functions
An interval from lower bound a to upper bound b is a possibly-infinite, possibly-empty set of numeric values of the same numeric type. Each bound will be described as either inclusive or exclusive, but not both. There are four kinds of intervals, as follows:
- An
interval from a (inclusive) to b (inclusive), also called an inclusive interval from a to b, includes all values x of the same numeric type such that a ≤ x ≤ b, and no others. - An
interval from a (inclusive) to b (exclusive) includes all values x of the same numeric type such that a ≤ x < b, and no others. - An
interval from a (exclusive) to b (inclusive) includes all values x of the same numeric type such that a < x ≤ b, and no others. - An
interval from a (exclusive) to b (exclusive) includes all values x of the same numeric type such that a < x < b, and no others.
For example, the
5.2.6 Value Notation
In this specification, Function.prototype.apply or let n = 42;.
5.2.7 Identity
In this specification, both specification values and
From the perspective of this specification, the word “is” is used to compare two values for equality, as in “If bool is
From the perspective of the ECMAScript language, language values are compared for equality using the
For specification values, examples of values without specification identity include, but are not limited to:
Specification identity agrees with language identity for all
6 ECMAScript Data Types and Values
Algorithms within this specification manipulate values each of which has an associated type. The possible value types are exactly those defined in this clause. Types are further classified into
6.1 ECMAScript Language Types
An ECMAScript language type corresponds to values that are directly manipulated by an ECMAScript programmer using the ECMAScript language. The ECMAScript language types are Undefined, Null, Boolean, String, Symbol, Number, BigInt, and Object. An ECMAScript language value is a value that is characterized by an ECMAScript language type.
6.1.1 The Undefined Type
The Undefined type has exactly one value, called
6.1.2 The Null Type
The Null type has exactly one value, called
6.1.3 The Boolean Type
The Boolean type represents a logical entity having two values, called
6.1.4 The String Type
The String type is the set of all ordered sequences of zero or more 16-bit unsigned
ECMAScript operations that do not interpret String contents apply no further semantics. Operations that do interpret String values treat each element as a single UTF-16 code unit. However, ECMAScript does not restrict the value of or relationships between these code units, so operations that further interpret String contents as sequences of Unicode code points encoded in UTF-16 must account for ill-formed subsequences. Such operations apply special treatment to every code unit with a numeric value in the
-
A code unit that is not a
leading surrogate and not atrailing surrogate is interpreted as a code point with the same value. -
A sequence of two code units, where the first code unit c1 is a
leading surrogate and the second code unit c2 atrailing surrogate , is a surrogate pair and is interpreted as a code point with the value (c1 - 0xD800) × 0x400 + (c2 - 0xDC00) + 0x10000. (See11.1.3 ) -
A code unit that is a
leading surrogate ortrailing surrogate , but is not part of asurrogate pair , is interpreted as a code point with the same value.
The function String.prototype.normalize (see String.prototype.localeCompare (see
The rationale behind this design was to keep the implementation of Strings as simple and high-performing as possible. If
In this specification, the phrase "the string-concatenation of A, B, ..." (where each argument is a String value, a code unit, or a sequence of code units) denotes the String value whose sequence of code units is the concatenation of the code units (in order) of each of the arguments (in order).
The phrase "the substring of S from inclusiveStart to exclusiveEnd" (where S is a String value or a sequence of code units and inclusiveStart and exclusiveEnd are
The phrase "the ASCII word characters" denotes the following String value, which consists solely of every letter and number in the Unicode Basic Latin block along with U+005F (LOW LINE):
For historical reasons, it has significance to various algorithms.
6.1.4.1 StringIndexOf ( string, searchValue, fromIndex )
The abstract operation StringIndexOf takes arguments string (a String), searchValue (a String), and fromIndex (a non-negative
- Let len be the length of string.
- If searchValue is the empty String and fromIndex ≤ len, return fromIndex.
- Let searchLen be the length of searchValue.
- For each
integer i such that fromIndex ≤ i ≤ len - searchLen, in ascending order, do- Let candidate be the
substring of string from i to i + searchLen. - If candidate is searchValue, return i.
- Let candidate be the
- Return
not-found .
If searchValue is the empty String and fromIndex ≤ the length of string, this algorithm returns fromIndex. The empty String is effectively found at every position within a string, including after the last code unit.
This algorithm always returns
6.1.4.2 StringLastIndexOf ( string, searchValue, fromIndex )
The abstract operation StringLastIndexOf takes arguments string (a String), searchValue (a String), and fromIndex (a non-negative
- Let len be the length of string.
- Let searchLen be the length of searchValue.
Assert : fromIndex + searchLen ≤ len.- For each
integer i such that 0 ≤ i ≤ fromIndex, in descending order, do- Let candidate be the
substring of string from i to i + searchLen. - If candidate is searchValue, return i.
- Let candidate be the
- Return
not-found .
If searchValue is the empty String, this algorithm returns fromIndex. The empty String is effectively found at every position within a string, including after the last code unit.
6.1.5 The Symbol Type
The Symbol type is the set of all non-String values that may be used as the key of an Object property (
Each possible Symbol value is unique and immutable.
Each Symbol value immutably holds an associated value called [[Description]] that is either
6.1.5.1 Well-Known Symbols
Well-known symbols are built-in Symbol values that are explicitly referenced by algorithms of this specification. They are typically used as the keys of properties whose values serve as extension points of a specification algorithm. Unless otherwise specified, well-known symbols values are shared by all
Within this specification a well-known symbol is referred to using the standard
%Symbol.name%. In particular, the following names were used: @@asyncIterator, @@hasInstance, @@isConcatSpreadable, @@| Specification Name | [[Description]] | Value and Purpose |
|---|---|---|
| %Symbol.asyncIterator% |
|
A method that returns the default for-await-of statement.
|
| %Symbol.hasInstance% |
|
A method that determines if a instanceof operator.
|
| %Symbol.isConcatSpreadable% |
|
A Boolean valued property that if true indicates that an object should be flattened to its array elements by Array.prototype.concat |
| %Symbol.iterator% |
|
A method that returns the default |
| %Symbol.match% |
|
A regular expression method that matches the regular expression against a string. Called by the String.prototype.match |
| %Symbol.matchAll% |
|
A regular expression method that returns an String.prototype.matchAll |
| %Symbol.replace% |
|
A regular expression method that replaces matched substrings of a string. Called by the String.prototype.replace |
| %Symbol.search% |
|
A regular expression method that returns the index within a string that matches the regular expression. Called by the String.prototype.search |
| %Symbol.species% |
|
A function valued property that is the |
| %Symbol.split% |
|
A regular expression method that splits a string at the indices that match the regular expression. Called by the String.prototype.split |
| %Symbol.toPrimitive% |
|
A method that converts an object to a corresponding primitive value. Called by the |
| %Symbol.toStringTag% |
|
A String valued property that is used in the creation of the default string description of an object. Accessed by the built-in method Object.prototype.toString |
| %Symbol.unscopables% |
|
An object valued property whose own and inherited property names are property names that are excluded from the with environment bindings of the associated object.
|
6.1.6 Numeric Types
ECMAScript has two built-in numeric types: Number and BigInt. The following
Because the numeric types are in general not convertible without loss of precision or truncation, the ECMAScript language provides no implicit conversion among these types. Programmers must explicitly call Number and BigInt functions to convert among types when calling a function which requires another type.
The first and subsequent editions of ECMAScript have provided, for certain operators, implicit numeric conversions that could lose precision or
6.1.6.1 The Number Type
The Number type has exactly 18,437,736,874,454,810,627 (that is, NaN.) In some implementations, external code might be able to detect a difference between various NaN values, but such behaviour is
There are two other special values, called +Infinity (or simply Infinity) and -Infinity.)
The other 18,437,736,874,454,810,624 (that is,
Note that there is both a +0 (or simply 0) and -0.)
The 18,437,736,874,454,810,622 (that is,
18,428,729,675,200,069,632 (that is,
where s is 1 or -1, m is an
The remaining 9,007,199,254,740,990 (that is,
where s is 1 or -1, m is an
Note that all the positive and negative
A
In this specification, the phrase “the Number value for x” where x represents an exact real mathematical quantity (which might even be an irrational number such as π) means a Number value chosen in the following manner. Consider the set of all
The
Some ECMAScript operators deal only with
6.1.6.1.1 Number::unaryMinus ( x )
The abstract operation Number::unaryMinus takes argument x (a Number) and returns a Number. It performs the following steps when called:
- If x is
NaN , returnNaN . - Return the negation of x; that is, compute a Number with the same magnitude but opposite sign.
6.1.6.1.2 Number::bitwiseNOT ( x )
The abstract operation Number::bitwiseNOT takes argument x (a Number) and returns an
- Let oldValue be !
ToInt32 (x). - Return the bitwise complement of oldValue. The
mathematical value of the result is exactly representable as a 32-bit two's complement bit string.
6.1.6.1.3 Number::exponentiate ( base, exponent )
The abstract operation Number::exponentiate takes arguments base (a Number) and exponent (a Number) and returns a Number. It returns an
- If exponent is
NaN , returnNaN . - If exponent is either
+0 𝔽 or-0 𝔽, return1 𝔽. - If base is
NaN , returnNaN . - If base is
+∞ 𝔽, then- If exponent >
+0 𝔽, return+∞ 𝔽. Otherwise, return+0 𝔽.
- If exponent >
- If base is
-∞ 𝔽, then- If exponent >
+0 𝔽, then- If exponent is an odd
integral Number , return-∞ 𝔽. Otherwise, return+∞ 𝔽.
- If exponent is an odd
- Else,
- If exponent is an odd
integral Number , return-0 𝔽. Otherwise, return+0 𝔽.
- If exponent is an odd
- If exponent >
- If base is
+0 𝔽, then- If exponent >
+0 𝔽, return+0 𝔽. Otherwise, return+∞ 𝔽.
- If exponent >
- If base is
-0 𝔽, then- If exponent >
+0 𝔽, then- If exponent is an odd
integral Number , return-0 𝔽. Otherwise, return+0 𝔽.
- If exponent is an odd
- Else,
- If exponent is an odd
integral Number , return-∞ 𝔽. Otherwise, return+∞ 𝔽.
- If exponent is an odd
- If exponent >
Assert : base isfinite and is neither+0 𝔽 nor-0 𝔽.- If exponent is
+∞ 𝔽, then - If exponent is
-∞ 𝔽, then Assert : exponent isfinite and is neither+0 𝔽 nor-0 𝔽.- If base <
-0 𝔽 and exponent is not anintegral Number , returnNaN . - Return an
implementation-approximated Number value representing the result of raisingℝ (base) to theℝ (exponent) power.
The result of base ** exponent when base is
6.1.6.1.4 Number::multiply ( x, y )
The abstract operation Number::multiply takes arguments x (a Number) and y (a Number) and returns a Number. It performs multiplication according to the rules of
- If x is
NaN or y isNaN , returnNaN . - If x is either
+∞ 𝔽 or-∞ 𝔽, then- If y is either
+0 𝔽 or-0 𝔽, returnNaN . - If y >
+0 𝔽, return x. - Return -x.
- If y is either
- If y is either
+∞ 𝔽 or-∞ 𝔽, then- If x is either
+0 𝔽 or-0 𝔽, returnNaN . - If x >
+0 𝔽, return y. - Return -y.
- If x is either
- If x is
-0 𝔽, then- If y is
-0 𝔽 or y <-0 𝔽, return+0 𝔽. - Else, return
-0 𝔽.
- If y is
- If y is
-0 𝔽, then- If x <
-0 𝔽, return+0 𝔽. - Else, return
-0 𝔽.
- If x <
- Return
𝔽 (ℝ (x) ×ℝ (y)).
6.1.6.1.5 Number::divide ( x, y )
The abstract operation Number::divide takes arguments x (a Number) and y (a Number) and returns a Number. It performs division according to the rules of
- If x is
NaN or y isNaN , returnNaN . - If x is either
+∞ 𝔽 or-∞ 𝔽, then- If y is either
+∞ 𝔽 or-∞ 𝔽, returnNaN . - If y is
+0 𝔽 or y >+0 𝔽, return x. - Return -x.
- If y is either
- If y is
+∞ 𝔽, then- If x is
+0 𝔽 or x >+0 𝔽, return+0 𝔽. Otherwise, return-0 𝔽.
- If x is
- If y is
-∞ 𝔽, then- If x is
+0 𝔽 or x >+0 𝔽, return-0 𝔽. Otherwise, return+0 𝔽.
- If x is
- If x is either
+0 𝔽 or-0 𝔽, then- If y is either
+0 𝔽 or-0 𝔽, returnNaN . - If y >
+0 𝔽, return x. - Return -x.
- If y is either
- If y is
+0 𝔽, then- If x >
+0 𝔽, return+∞ 𝔽. Otherwise, return-∞ 𝔽.
- If x >
- If y is
-0 𝔽, then- If x >
+0 𝔽, return-∞ 𝔽. Otherwise, return+∞ 𝔽.
- If x >
- Return
𝔽 (ℝ (x) /ℝ (y)).
6.1.6.1.6 Number::remainder ( n, d )
The abstract operation Number::remainder takes arguments n (a Number) and d (a Number) and returns a Number. It yields the remainder from an implied division of its operands where n is the dividend and d is the divisor. It performs the following steps when called:
- If n is
NaN or d isNaN , returnNaN . - If n is either
+∞ 𝔽 or-∞ 𝔽, returnNaN . - If d is either
+∞ 𝔽 or-∞ 𝔽, return n. - If d is either
+0 𝔽 or-0 𝔽, returnNaN . - If n is either
+0 𝔽 or-0 𝔽, return n. Assert : n and d arefinite and non-zero.- Let quotient be
ℝ (n) /ℝ (d). - Let q be
truncate (quotient). - Let r be
ℝ (n) - (ℝ (d) × q). - If r = 0 and n <
-0 𝔽, return-0 𝔽. - Return
𝔽 (r).
In C and C++, the remainder operator accepts only integral operands; in ECMAScript, it also accepts floating-point operands.
% operator is not the same as the “remainder” operation defined by % on floating-point operations to behave in a manner analogous to that of the Java 6.1.6.1.7 Number::add ( x, y )
The abstract operation Number::add takes arguments x (a Number) and y (a Number) and returns a Number. It performs addition according to the rules of
6.1.6.1.8 Number::subtract ( x, y )
The abstract operation Number::subtract takes arguments x (a Number) and y (a Number) and returns a Number. It performs subtraction, producing the difference of its operands; x is the minuend and y is the subtrahend. It performs the following steps when called:
- Return
Number::add (x,Number::unaryMinus (y)).
It is always the case that x - y produces the same result as x + (-y).
6.1.6.1.9 Number::leftShift ( x, y )
The abstract operation Number::leftShift takes arguments x (a Number) and y (a Number) and returns an
- Let lNum be !
ToInt32 (x). - Let rNum be !
ToUint32 (y). - Let shiftCount be
ℝ (rNum)modulo 32. - Return the result of left shifting lNum by shiftCount bits. The
mathematical value of the result is exactly representable as a 32-bit two's complement bit string.
6.1.6.1.10 Number::signedRightShift ( x, y )
The abstract operation Number::signedRightShift takes arguments x (a Number) and y (a Number) and returns an
- Let lNum be !
ToInt32 (x). - Let rNum be !
ToUint32 (y). - Let shiftCount be
ℝ (rNum)modulo 32. - Return the result of performing a sign-extending right shift of lNum by shiftCount bits. The most significant bit is propagated. The
mathematical value of the result is exactly representable as a 32-bit two's complement bit string.
6.1.6.1.11 Number::unsignedRightShift ( x, y )
The abstract operation Number::unsignedRightShift takes arguments x (a Number) and y (a Number) and returns an
- Let lNum be !
ToUint32 (x). - Let rNum be !
ToUint32 (y). - Let shiftCount be
ℝ (rNum)modulo 32. - Return the result of performing a zero-filling right shift of lNum by shiftCount bits. Vacated bits are filled with zero. The
mathematical value of the result is exactly representable as a 32-bit unsigned bit string.
6.1.6.1.12 Number::lessThan ( x, y )
The abstract operation Number::lessThan takes arguments x (a Number) and y (a Number) and returns a Boolean or
- If x is
NaN , returnundefined . - If y is
NaN , returnundefined . - If x is y, return
false . - If x is
+0 𝔽 and y is-0 𝔽, returnfalse . - If x is
-0 𝔽 and y is+0 𝔽, returnfalse . - If x is
+∞ 𝔽, returnfalse . - If y is
+∞ 𝔽, returntrue . - If y is
-∞ 𝔽, returnfalse . - If x is
-∞ 𝔽, returntrue . Assert : x and y arefinite .- If
ℝ (x) <ℝ (y), returntrue . Otherwise, returnfalse .
6.1.6.1.13 Number::equal ( x, y )
The abstract operation Number::equal takes arguments x (a Number) and y (a Number) and returns a Boolean. It performs the following steps when called:
- If x is
NaN , returnfalse . - If y is
NaN , returnfalse . - If x is y, return
true . - If x is
+0 𝔽 and y is-0 𝔽, returntrue . - If x is
-0 𝔽 and y is+0 𝔽, returntrue . - Return
false .
6.1.6.1.14 Number::sameValue ( x, y )
The abstract operation Number::sameValue takes arguments x (a Number) and y (a Number) and returns a Boolean. It performs the following steps when called:
- If x is
NaN and y isNaN , returntrue . - If x is
+0 𝔽 and y is-0 𝔽, returnfalse . - If x is
-0 𝔽 and y is+0 𝔽, returnfalse . - If x is y, return
true . - Return
false .
6.1.6.1.15 Number::sameValueZero ( x, y )
The abstract operation Number::sameValueZero takes arguments x (a Number) and y (a Number) and returns a Boolean. It performs the following steps when called:
- If x is
NaN and y isNaN , returntrue . - If x is
+0 𝔽 and y is-0 𝔽, returntrue . - If x is
-0 𝔽 and y is+0 𝔽, returntrue . - If x is y, return
true . - Return
false .
6.1.6.1.16 NumberBitwiseOp ( op, x, y )
The abstract operation NumberBitwiseOp takes arguments op (&, ^, or |), x (a Number), and y (a Number) and returns an
- Let lNum be !
ToInt32 (x). - Let rNum be !
ToInt32 (y). - Let lBits be the 32-bit two's complement bit string representing
ℝ (lNum). - Let rBits be the 32-bit two's complement bit string representing
ℝ (rNum). - If op is
&, then- Let result be the result of applying the bitwise AND operation to lBits and rBits.
- Else if op is
^, then- Let result be the result of applying the bitwise exclusive OR (XOR) operation to lBits and rBits.
- Else,
Assert : op is|.- Let result be the result of applying the bitwise inclusive OR operation to lBits and rBits.
- Return the
Number value for theinteger represented by the 32-bit two's complement bit string result.
6.1.6.1.17 Number::bitwiseAND ( x, y )
The abstract operation Number::bitwiseAND takes arguments x (a Number) and y (a Number) and returns an
- Return
NumberBitwiseOp (&, x, y).
6.1.6.1.18 Number::bitwiseXOR ( x, y )
The abstract operation Number::bitwiseXOR takes arguments x (a Number) and y (a Number) and returns an
- Return
NumberBitwiseOp (^, x, y).
6.1.6.1.19 Number::bitwiseOR ( x, y )
The abstract operation Number::bitwiseOR takes arguments x (a Number) and y (a Number) and returns an
- Return
NumberBitwiseOp (|, x, y).
6.1.6.1.20 Number::toString ( x, radix )
The abstract operation Number::toString takes arguments x (a Number) and radix (an
- If x is
NaN , return"NaN" . - If x is either
+0 𝔽 or-0 𝔽, return"0" . - If x <
-0 𝔽, return thestring-concatenation of"-" andNumber::toString (-x, radix). - If x is
+∞ 𝔽, return"Infinity" . - Let n, k, and s be
integers such that k ≥ 1, radixk - 1 ≤ s < radixk,𝔽 (s × radixn - k) is x, and k is as small as possible. Note that k is the number of digits in the representation of s using radix radix, that s is not divisible by radix, and that the least significant digit of s is not necessarily uniquely determined by these criteria. - If radix ≠ 10 or n is in the
inclusive interval from -5 to 21, then- If n ≥ k, then
- Return the
string-concatenation of:- the code units of the k digits of the representation of s using radix radix
- n - k occurrences of the code unit 0x0030 (DIGIT ZERO)
- Return the
- Else if n > 0, then
- Return the
string-concatenation of:- the code units of the most significant n digits of the representation of s using radix radix
- the code unit 0x002E (FULL STOP)
- the code units of the remaining k - n digits of the representation of s using radix radix
- Return the
- Else,
Assert : n ≤ 0.- Return the
string-concatenation of:- the code unit 0x0030 (DIGIT ZERO)
- the code unit 0x002E (FULL STOP)
- -n occurrences of the code unit 0x0030 (DIGIT ZERO)
- the code units of the k digits of the representation of s using radix radix
- If n ≥ k, then
- NOTE: In this case, the input will be represented using scientific E notation, such as
1.2e+3. Assert : radix is 10.- If n < 0, then
- Let exponentSign be the code unit 0x002D (HYPHEN-MINUS).
- Else,
- Let exponentSign be the code unit 0x002B (PLUS SIGN).
- If k = 1, then
- Return the
string-concatenation of:- the code unit of the single digit of s
- the code unit 0x0065 (LATIN SMALL LETTER E)
- exponentSign
- the code units of the decimal representation of
abs (n - 1)
- Return the
- Return the
string-concatenation of:- the code unit of the most significant digit of the decimal representation of s
- the code unit 0x002E (FULL STOP)
- the code units of the remaining k - 1 digits of the decimal representation of s
- the code unit 0x0065 (LATIN SMALL LETTER E)
- exponentSign
- the code units of the decimal representation of
abs (n - 1)
The following observations may be useful as guidelines for implementations, but are not part of the normative requirements of this Standard:
For implementations that provide more accurate conversions than required by the rules above, it is recommended that the following alternative version of step
- Let n, k, and s be
integers such that k ≥ 1, radixk - 1 ≤ s < radixk,𝔽 (s × radixn - k) is x, and k is as small as possible. If there are multiple possibilities for s, choose the value of s for which s × radixn - k is closest in value toℝ (x). If there are two such possible values of s, choose the one that is even. Note that k is the number of digits in the representation of s using radix radix and that s is not divisible by radix.
Implementers of ECMAScript may find useful the paper and code written by David M. Gay for binary-to-decimal conversion of floating-point numbers:
Gay, David M. Correctly Rounded Binary-Decimal and Decimal-Binary Conversions. Numerical Analysis, Manuscript 90-10. AT&T Bell Laboratories (Murray Hill, New Jersey). 30 November 1990. Available as
https://ampl.com/_archive/first-website/REFS/rounding.pdf. Associated code available as
http://netlib.sandia.gov/fp/dtoa.c and as
http://netlib.sandia.gov/fp/g_fmt.c and may also be found at the various netlib mirror sites.
6.1.6.2 The BigInt Type
The BigInt type represents an
6.1.6.2.1 BigInt::unaryMinus ( x )
The abstract operation BigInt::unaryMinus takes argument x (a BigInt) and returns a BigInt. It performs the following steps when called:
- If x =
0 ℤ, return0 ℤ. - Return -x.
6.1.6.2.2 BigInt::bitwiseNOT ( x )
The abstract operation BigInt::bitwiseNOT takes argument x (a BigInt) and returns a BigInt. It returns the one's complement of x. It performs the following steps when called:
- Return -x -
1 ℤ.
6.1.6.2.3 BigInt::exponentiate ( base, exponent )
The abstract operation BigInt::exponentiate takes arguments base (a BigInt) and exponent (a BigInt) and returns either a
- If exponent <
0 ℤ, throw aRangeError exception. - If base =
0 ℤ and exponent =0 ℤ, return1 ℤ. - Return base raised to the power exponent.
6.1.6.2.4 BigInt::multiply ( x, y )
The abstract operation BigInt::multiply takes arguments x (a BigInt) and y (a BigInt) and returns a BigInt. It performs the following steps when called:
- Return x × y.
6.1.6.2.5 BigInt::divide ( x, y )
The abstract operation BigInt::divide takes arguments x (a BigInt) and y (a BigInt) and returns either a
6.1.6.2.6 BigInt::remainder ( n, d )
The abstract operation BigInt::remainder takes arguments n (a BigInt) and d (a BigInt) and returns either a
6.1.6.2.7 BigInt::add ( x, y )
The abstract operation BigInt::add takes arguments x (a BigInt) and y (a BigInt) and returns a BigInt. It performs the following steps when called:
- Return x + y.
6.1.6.2.8 BigInt::subtract ( x, y )
The abstract operation BigInt::subtract takes arguments x (a BigInt) and y (a BigInt) and returns a BigInt. It performs the following steps when called:
- Return x - y.
6.1.6.2.9 BigInt::leftShift ( x, y )
The abstract operation BigInt::leftShift takes arguments x (a BigInt) and y (a BigInt) and returns a BigInt. It performs the following steps when called:
6.1.6.2.10 BigInt::signedRightShift ( x, y )
The abstract operation BigInt::signedRightShift takes arguments x (a BigInt) and y (a BigInt) and returns a BigInt. It performs the following steps when called:
- Return
BigInt::leftShift (x, -y).
6.1.6.2.11 BigInt::unsignedRightShift ( x, y )
The abstract operation BigInt::unsignedRightShift takes arguments x (a BigInt) and y (a BigInt) and returns a
- Throw a
TypeError exception.
6.1.6.2.12 BigInt::lessThan ( x, y )
The abstract operation BigInt::lessThan takes arguments x (a BigInt) and y (a BigInt) and returns a Boolean. It performs the following steps when called:
6.1.6.2.13 BigInt::equal ( x, y )
The abstract operation BigInt::equal takes arguments x (a BigInt) and y (a BigInt) and returns a Boolean. It performs the following steps when called:
6.1.6.2.14 BinaryAnd ( x, y )
The abstract operation BinaryAnd takes arguments x (0 or 1) and y (0 or 1) and returns 0 or 1. It performs the following steps when called:
- If x = 1 and y = 1, return 1.
- Else, return 0.
6.1.6.2.15 BinaryOr ( x, y )
The abstract operation BinaryOr takes arguments x (0 or 1) and y (0 or 1) and returns 0 or 1. It performs the following steps when called:
- If x = 1 or y = 1, return 1.
- Else, return 0.
6.1.6.2.16 BinaryXor ( x, y )
The abstract operation BinaryXor takes arguments x (0 or 1) and y (0 or 1) and returns 0 or 1. It performs the following steps when called:
- If x = 1 and y = 0, return 1.
- Else if x = 0 and y = 1, return 1.
- Else, return 0.
6.1.6.2.17 BigIntBitwiseOp ( op, x, y )
The abstract operation BigIntBitwiseOp takes arguments op (&, ^, or |), x (a BigInt), and y (a BigInt) and returns a BigInt. It performs the following steps when called:
- Set x to
ℝ (x). - Set y to
ℝ (y). - Let result be 0.
- Let shift be 0.
- Repeat, until (x = 0 or x = -1) and (y = 0 or y = -1),
- If op is
&, then - Else if op is
|, then - Else,
- If tmp ≠ 0, then
- Set result to result - 2shift.
- NOTE: This extends the sign.
- Return the
BigInt value for result.
6.1.6.2.18 BigInt::bitwiseAND ( x, y )
The abstract operation BigInt::bitwiseAND takes arguments x (a BigInt) and y (a BigInt) and returns a BigInt. It performs the following steps when called:
- Return
BigIntBitwiseOp (&, x, y).
6.1.6.2.19 BigInt::bitwiseXOR ( x, y )
The abstract operation BigInt::bitwiseXOR takes arguments x (a BigInt) and y (a BigInt) and returns a BigInt. It performs the following steps when called:
- Return
BigIntBitwiseOp (^, x, y).
6.1.6.2.20 BigInt::bitwiseOR ( x, y )
The abstract operation BigInt::bitwiseOR takes arguments x (a BigInt) and y (a BigInt) and returns a BigInt. It performs the following steps when called:
- Return
BigIntBitwiseOp (|, x, y).
6.1.6.2.21 BigInt::toString ( x, radix )
The abstract operation BigInt::toString takes arguments x (a BigInt) and radix (an
- If x <
0 ℤ, return thestring-concatenation of"-" andBigInt::toString (-x, radix). - Return the String value consisting of the representation of x using radix radix.
6.1.7 The Object Type
Each instance of the Object type, also referred to simply as “an Object”, represents a collection of properties. Each property is either a data property, or an accessor property:
-
A data property associates a key value with an
ECMAScript language value and a set of Boolean attributes. -
An accessor property associates a key value with one or two accessor functions, and a set of Boolean attributes. The accessor functions are used to store or retrieve an
ECMAScript language value that is associated with the property.
The properties of an object are uniquely identified using
An integer index is a
Every non-negative
All objects are logically collections of properties, but there are multiple forms of objects that differ in their semantics for accessing and manipulating their properties. Please see
In addition, some objects are callable; these are referred to as functions or
6.1.7.1 Property Attributes
Attributes are used in this specification to define and explain the state of Object properties as described in
| Attribute Name | Types of property for which it is present | Value Domain | Default Value | Description |
|---|---|---|---|---|
| [[Value]] |
|
an |
|
The value retrieved by a get access of the property. |
| [[Writable]] |
|
a Boolean |
|
If |
| [[Get]] |
|
an Object or |
|
If the value |
| [[Set]] |
|
an Object or |
|
If the value |
| [[Enumerable]] |
|
a Boolean |
|
If |
| [[Configurable]] |
|
a Boolean |
|
If |
6.1.7.2 Object Internal Methods and Internal Slots
The actual semantics of objects, in ECMAScript, are specified via algorithms called internal methods. Each object in an ECMAScript engine is associated with a set of internal methods that defines its runtime behaviour. These internal methods are not part of the ECMAScript language. They are defined by this specification purely for expository purposes. However, each object within an implementation of ECMAScript must behave as specified by the internal methods associated with it. The exact manner in which this is accomplished is determined by the implementation.
Internal method names are polymorphic. This means that different object values may perform different algorithms when a common internal method name is invoked upon them. That actual object upon which an internal method is invoked is the “target” of the invocation. If, at runtime, the implementation of an algorithm attempts to use an internal method of an object that the object does not support, a
Internal slots correspond to internal state that is associated with objects and used by various ECMAScript specification algorithms. Internal slots are not object properties and they are not inherited. Depending upon the specific internal slot specification, such state may consist of values of any
All objects have an internal slot named [[PrivateElements]], which is a
Internal methods and internal slots are identified within this specification using names enclosed in double square brackets [[ ]].
An ordinary object is an object that satisfies all of the following criteria:
-
For the internal methods listed in
Table 4 , the object uses those defined in10.1 . -
If the object has a [[Call]] internal method, it uses either the one defined in
10.2.1 or the one defined in10.3.1 . -
If the object has a [[Construct]] internal method, it uses either the one defined in
10.2.2 or the one defined in10.3.2 .
An exotic object is an object that is not an
This specification recognizes different kinds of
The “Signature” column of
In addition to its parameters, an internal method always has access to the object that is the target of the method invocation.
An internal method implicitly returns a
| Internal Method | Signature | Description |
|---|---|---|
| [[GetPrototypeOf]] | ( ) → Object | Null |
Determine the object that provides inherited properties for this object. A |
| [[SetPrototypeOf]] | (Object | Null) → Boolean |
Associate this object with another object that provides inherited properties. Passing |
| [[IsExtensible]] | ( ) → Boolean | Determine whether it is permitted to add additional properties to this object. |
| [[PreventExtensions]] | ( ) → Boolean |
Control whether new properties may be added to this object. Returns |
| [[GetOwnProperty]] |
(propertyKey) → Undefined | |
Return a |
| [[DefineOwnProperty]] | (propertyKey, PropertyDescriptor) → Boolean |
Create or alter the own property, whose key is propertyKey, to have the state described by PropertyDescriptor. Return |
| [[HasProperty]] | (propertyKey) → Boolean | Return a Boolean value indicating whether this object already has either an own or inherited property whose key is propertyKey. |
| [[Get]] | (propertyKey, Receiver) → any |
Return the value of the property whose key is propertyKey from this object. If any ECMAScript code must be executed to retrieve the property value, Receiver is used as the |
| [[Set]] | (propertyKey, value, Receiver) → Boolean |
Set the value of the property whose key is propertyKey to value. If any ECMAScript code must be executed to set the property value, Receiver is used as the |
| [[Delete]] | (propertyKey) → Boolean |
Remove the own property whose key is propertyKey from this object. Return |
| [[OwnPropertyKeys]] |
( ) → |
Return a |
| Internal Method | Signature | Description |
|---|---|---|
| [[Call]] |
(any, a |
Executes code associated with this object. Invoked via a function call expression. The arguments to the internal method are a |
| [[Construct]] |
(a |
Creates an object. Invoked via the new operator or a super call. The first argument to the internal method is a super call. The second argument is the object to which the new operator was initially applied. Objects that implement this internal method are called |
The semantics of the essential internal methods for
6.1.7.3 Invariants of the Essential Internal Methods
The Internal Methods of Objects of an ECMAScript engine must conform to the list of invariants specified below. Ordinary ECMAScript Objects as well as all standard
Any implementation provided
An implementation must not allow these invariants to be circumvented in any manner such as by providing alternative interfaces that implement the functionality of the essential internal methods without enforcing their invariants.
Definitions:
- The target of an internal method is the object upon which the internal method is called.
-
A target is non-extensible if it has been observed to return
false from its [[IsExtensible]] internal method, ortrue from its [[PreventExtensions]] internal method. - A non-existent property is a property that does not exist as an own property on a non-extensible target.
-
All references to
SameValue are according to the definition of theSameValue algorithm.
Return value:
The value returned by any internal method must be a
- [[Type]] =
normal , [[Target]] =empty , and [[Value]] = a value of the "normal return type" shown below for that internal method, or - [[Type]] =
throw , [[Target]] =empty , and [[Value]] = anyECMAScript language value .
An internal method must not return a
[[GetPrototypeOf]] ( )
- The normal return type is either Object or Null.
-
If target is non-extensible, and [[GetPrototypeOf]] returns a value V, then any future calls to [[GetPrototypeOf]] should return the
SameValue as V.
An object's prototype chain should have
[[SetPrototypeOf]] ( V )
- The normal return type is Boolean.
-
If target is non-extensible, [[SetPrototypeOf]] must return
false , unless V is theSameValue as the target's observed [[GetPrototypeOf]] value.
[[IsExtensible]] ( )
- The normal return type is Boolean.
-
If [[IsExtensible]] returns
false , all future calls to [[IsExtensible]] on the target must returnfalse .
[[PreventExtensions]] ( )
- The normal return type is Boolean.
-
If [[PreventExtensions]] returns
true , all future calls to [[IsExtensible]] on the target must returnfalse and the target is now considered non-extensible.
[[GetOwnProperty]] ( P )
-
The normal return type is either
Property Descriptor or Undefined. -
If the return value is a
Property Descriptor , it must be afully populated Property Descriptor . -
If P is described as a non-configurable, non-writable own
data property , all future calls to [[GetOwnProperty]] ( P ) must returnProperty Descriptor whose [[Value]] isSameValue as P's [[Value]] attribute. -
If P's attributes other than [[Writable]] and [[Value]] may change over time, or if the property might be deleted, then P's [[Configurable]] attribute must be
true . -
If the [[Writable]] attribute may change from
false totrue , then the [[Configurable]] attribute must betrue . -
If the target is non-extensible and P is non-existent, then all future calls to [[GetOwnProperty]] (P) on the target must describe P as non-existent (i.e. [[GetOwnProperty]] (P) must return
undefined ).
As a consequence of the third invariant, if a property is described as a
[[DefineOwnProperty]] ( P, Desc )
- The normal return type is Boolean.
-
[[DefineOwnProperty]] must return
false if P has previously been observed as a non-configurable own property of the target, unless either:-
P is a writable
data property . A non-configurable writabledata property can be changed into a non-configurable non-writabledata property . -
All attributes of Desc are the
SameValue as P's attributes.
-
P is a writable
-
[[DefineOwnProperty]] (P, Desc) must return
false if target is non-extensible and P is a non-existent own property. That is, a non-extensible target object cannot be extended with new properties.
[[HasProperty]] ( P )
- The normal return type is Boolean.
-
If P was previously observed as a non-configurable own data or
accessor property of the target, [[HasProperty]] must returntrue .
[[Get]] ( P, Receiver )
-
The normal return type is any
ECMAScript language type . -
If P was previously observed as a non-configurable, non-writable own
data property of the target with value V, then [[Get]] must return theSameValue as V. -
If P was previously observed as a non-configurable own
accessor property of the target whose [[Get]] attribute isundefined , the [[Get]] operation must returnundefined .
[[Set]] ( P, V, Receiver )
- The normal return type is Boolean.
-
If P was previously observed as a non-configurable, non-writable own
data property of the target, then [[Set]] must returnfalse unless V is theSameValue as P's [[Value]] attribute. -
If P was previously observed as a non-configurable own
accessor property of the target whose [[Set]] attribute isundefined , the [[Set]] operation must returnfalse .
[[Delete]] ( P )
- The normal return type is Boolean.
-
If P was previously observed as a non-configurable own data or
accessor property of the target, [[Delete]] must returnfalse .
[[OwnPropertyKeys]] ( )
-
The normal return type is
List . -
The returned
List must not contain any duplicate entries. -
Each element of the returned
List must be aproperty key . -
The returned
List must contain at least the keys of all non-configurable own properties that have previously been observed. -
If the target is non-extensible, the returned
List must contain only the keys of all own properties of the target that are observable using [[GetOwnProperty]].
[[Call]] ( )
-
The normal return type is any
ECMAScript language type .
[[Construct]] ( )
- The normal return type is Object.
- The target must also have a [[Call]] internal method.
6.1.7.4 Well-Known Intrinsic Objects
Well-known intrinsics are built-in objects that are explicitly referenced by the algorithms of this specification and which usually have
Within this specification a reference such as %name% means the intrinsic object, associated with the current
| Intrinsic Name | Global Name | ECMAScript Language Association |
|---|---|---|
|
|
AggregateError
|
The AggregateError |
|
|
Array
|
The Array |
|
|
ArrayBuffer
|
The ArrayBuffer |
|
|
The prototype of |
|
|
|
The prototype of |
|
|
|
The |
|
|
|
The |
|
|
|
The prototype of async generator objects ( |
|
|
|
An object that all standard built-in |
|
|
|
Atomics
|
The Atomics object ( |
|
|
BigInt
|
The BigInt |
|
|
BigInt64Array
|
The BigInt64Array |
|
|
BigUint64Array
|
The BigUint64Array |
|
|
Boolean
|
The Boolean |
|
|
DataView
|
The DataView |
|
|
Date
|
The Date |
|
|
decodeURI
|
The decodeURI function ( |
|
|
decodeURIComponent
|
The decodeURIComponent function ( |
|
|
encodeURI
|
The encodeURI function ( |
|
|
encodeURIComponent
|
The encodeURIComponent function ( |
|
|
Error
|
The Error |
|
|
eval
|
The eval function ( |
|
|
EvalError
|
The EvalError |
|
|
FinalizationRegistry
|
The |
|
|
Float16Array
|
The Float16Array |
|
|
Float32Array
|
The Float32Array |
|
|
Float64Array
|
The Float64Array |
|
|
The prototype of |
|
|
|
Function
|
The Function |
|
|
The |
|
|
|
The prototype of generator objects ( |
|
|
|
Int8Array
|
The Int8Array |
|
|
Int16Array
|
The Int16Array |
|
|
Int32Array
|
The Int32Array |
|
|
isFinite
|
The isFinite function ( |
|
|
isNaN
|
The isNaN function ( |
|
|
Iterator
|
The Iterator |
|
|
The prototype of |
|
|
|
JSON
|
The JSON object ( |
|
|
Map
|
The Map |
|
|
The prototype of |
|
|
|
Math
|
The Math object ( |
|
|
Number
|
The Number |
|
|
Object
|
The Object |
|
|
parseFloat
|
The parseFloat function ( |
|
|
parseInt
|
The parseInt function ( |
|
|
Promise
|
The Promise |
|
|
Proxy
|
The Proxy |
|
|
RangeError
|
The RangeError |
|
|
ReferenceError
|
The ReferenceError |
|
|
Reflect
|
The Reflect object ( |
|
|
RegExp
|
The RegExp |
|
|
The prototype of |
|
|
|
Set
|
The Set |
|
|
The prototype of |
|
|
|
SharedArrayBuffer
|
The SharedArrayBuffer |
|
|
String
|
The String |
|
|
The prototype of |
|
|
|
Symbol
|
The Symbol |
|
|
SyntaxError
|
The SyntaxError |
|
|
A |
|
|
|
The super class of all typed Array |
|
|
|
TypeError
|
The TypeError |
|
|
Uint8Array
|
The Uint8Array |
|
|
Uint8ClampedArray
|
The Uint8ClampedArray |
|
|
Uint16Array
|
The Uint16Array |
|
|
Uint32Array
|
The Uint32Array |
|
|
URIError
|
The URIError |
|
|
WeakMap
|
The WeakMap |
|
|
WeakRef
|
The |
|
|
WeakSet
|
The WeakSet |
|
|
The prototype of wrapped |
Additional entries in
6.2 ECMAScript Specification Types
A specification type corresponds to meta-values that are used within algorithms to describe the semantics of ECMAScript language constructs and
6.2.1 The Enum Specification Type
Enums are values which are internal to the specification and not directly observable from ECMAScript code. Enums are denoted using a
6.2.2 The List and Record Specification Types
The List type is used to explain the evaluation of argument lists (see new expressions, in function calls, and in other algorithms where a simple ordered list of values is needed. Values of the List type are simply ordered sequences of list elements containing the individual values. These sequences may be of any length. The elements of a list may be randomly accessed using 0-origin indices. For notational convenience an array-like syntax can be used to access List elements. For example, arguments[2] is shorthand for saying the 3rd element of the List arguments.
When an algorithm iterates over the elements of a List without specifying an order, the order used is the order of the elements in the List.
For notational convenience within this specification, a literal syntax can be used to express a new List value. For example, « 1, 2 » defines a List value that has two elements each of which is initialized to a specific value. A new empty List can be expressed as « ».
In this specification, the phrase "the list-concatenation of A, B, ..." (where each argument is a possibly empty List) denotes a new List value whose elements are the concatenation of the elements (in order) of each of the arguments (in order).
As applied to a List of Strings, the phrase "sorted according to lexicographic code unit order" means sorting by the numeric value of each code unit up to the length of the shorter string, and sorting the shorter string before the longer string if all are equal, as described in the abstract operation
The Record type is used to describe data aggregations within the algorithms of this specification. A Record type value consists of one or more named fields. The value of each field is an
For notational convenience within this specification, an object literal-like syntax can be used to express a Record value. For example, { [[Field1]]: 42, [[Field2]]:
In specification text and algorithms, dot notation may be used to refer to a specific field of a Record value. For example, if R is the record shown in the previous paragraph then R.[[Field2]] is shorthand for “the field of R named [[Field2]]”.
Schema for commonly used Record field combinations may be named, and that name may be used as a prefix to a literal Record value to identify the specific kind of aggregations that is being described. For example: PropertyDescriptor { [[Value]]: 42, [[Writable]]:
6.2.3 The Set and Relation Specification Types
The Set type is used to explain a collection of unordered elements for use in the
The Relation type is used to explain constraints on Sets. Values of the Relation type are Sets of ordered pairs of values from its value domain. For example, a Relation on events is a set of ordered pairs of events. For a Relation R and two values a and b in the value domain of R, a R b is shorthand for saying the ordered pair (a, b) is a member of R. A Relation is the least Relation with respect to some conditions when it is the smallest Relation that satisfies those conditions.
A strict partial order is a Relation value R that satisfies the following.
-
For all a, b, and c in R's domain:
- It is not the case that a R a, and
- If a R b and b R c, then a R c.
The two properties above are called irreflexivity and transitivity, respectively.
A strict total order is a Relation value R that satisfies the following.
-
For all a, b, and c in R's domain:
- a is b or a R b or b R a, and
- It is not the case that a R a, and
- If a R b and b R c, then a R c.
The three properties above are called totality, irreflexivity, and transitivity, respectively.
6.2.4 The Completion Record Specification Type
The Completion Record specification type is used to explain the runtime propagation of values and control flow such as the behaviour of statements (break, continue, return and throw) that perform nonlocal transfers of control.
Completion Records have the fields defined in
| Field Name | Value | Meaning |
|---|---|---|
| [[Type]] |
|
The type of completion that occurred. |
| [[Value]] |
any value except a |
The value that was produced. |
| [[Target]] |
a String or |
The target label for directed control transfers. |
The following shorthand terms are sometimes used to refer to Completion Records.
- normal completion refers to any Completion Record with a [[Type]] value of
normal . - break completion refers to any Completion Record with a [[Type]] value of
break . - continue completion refers to any Completion Record with a [[Type]] value of
continue . - return completion refers to any Completion Record with a [[Type]] value of
return . - throw completion refers to any Completion Record with a [[Type]] value of
throw . - abrupt completion refers to any Completion Record with a [[Type]] value other than
normal . - a normal completion containing some type of value refers to a normal completion that has a value of that type in its [[Value]] field.
Callable objects that are defined in this specification only return a normal completion or a throw completion. Returning any other kind of Completion Record is considered an editorial error.
6.2.4.1 NormalCompletion ( value )
The abstract operation NormalCompletion takes argument value (any value except a
- Return
Completion Record { [[Type]]:normal , [[Value]]: value, [[Target]]:empty }.
6.2.4.2 ThrowCompletion ( value )
The abstract operation ThrowCompletion takes argument value (an
- Return
Completion Record { [[Type]]:throw , [[Value]]: value, [[Target]]:empty }.
6.2.4.3 ReturnCompletion ( value )
The abstract operation ReturnCompletion takes argument value (an
- Return
Completion Record { [[Type]]:return , [[Value]]: value, [[Target]]:empty }.
6.2.4.4 UpdateEmpty ( completionRecord, value )
The abstract operation UpdateEmpty takes arguments completionRecord (a
Assert : If completionRecord is either areturn completion or athrow completion , then completionRecord.[[Value]] is notempty .- If completionRecord.[[Value]] is not
empty , return ? completionRecord. - Return
Completion Record { [[Type]]: completionRecord.[[Type]], [[Value]]: value, [[Target]]: completionRecord.[[Target]] }.
6.2.5 The Reference Record Specification Type
The Reference Record type is used to explain the behaviour of such operators as delete, typeof, the assignment operators, the super
A Reference Record is a resolved name or (possibly not-yet-resolved) property binding; its fields are defined by
| Field Name | Value | Meaning |
|---|---|---|
| [[Base]] | an |
The value or |
| [[ReferencedName]] | an |
The name of the binding. Always a String if [[Base]] value is an |
| [[Strict]] | a Boolean | |
| [[ThisValue]] | an |
If not super |
The following
6.2.5.1 IsPropertyReference ( V )
The abstract operation IsPropertyReference takes argument V (a
- If V.[[Base]] is
unresolvable , returnfalse . - If V.[[Base]] is an
Environment Record , returnfalse ; otherwise returntrue .
6.2.5.2 IsUnresolvableReference ( V )
The abstract operation IsUnresolvableReference takes argument V (a
- If V.[[Base]] is
unresolvable , returntrue ; otherwise returnfalse .
6.2.5.3 IsSuperReference ( V )
The abstract operation IsSuperReference takes argument V (a
- If V.[[ThisValue]] is not
empty , returntrue ; otherwise returnfalse .
6.2.5.4 IsPrivateReference ( V )
The abstract operation IsPrivateReference takes argument V (a
- If V.[[ReferencedName]] is a
Private Name , returntrue ; otherwise returnfalse .
6.2.5.5 GetValue ( V )
The abstract operation GetValue takes argument V (a
- If V is not a
Reference Record , return V. - If
IsUnresolvableReference (V) istrue , throw aReferenceError exception. - If
IsPropertyReference (V) istrue , then- Let baseObj be ?
ToObject (V.[[Base]]). - If
IsPrivateReference (V) istrue , then- Return ?
PrivateGet (baseObj, V.[[ReferencedName]]).
- Return ?
- If V.[[ReferencedName]] is not a
property key , then- Set V.[[ReferencedName]] to ?
ToPropertyKey (V.[[ReferencedName]]).
- Set V.[[ReferencedName]] to ?
- Return ? baseObj.[[Get]](V.[[ReferencedName]],
GetThisValue (V)).
- Let baseObj be ?
- Else,
- Let base be V.[[Base]].
Assert : base is anEnvironment Record .- Return ? base.GetBindingValue(V.[[ReferencedName]], V.[[Strict]]) (see
9.1 ).
The object that may be created in step
6.2.5.6 PutValue ( V, W )
The abstract operation PutValue takes arguments V (a
- If V is not a
Reference Record , throw aReferenceError exception. - If
IsUnresolvableReference (V) istrue , then- If V.[[Strict]] is
true , throw aReferenceError exception. - Let globalObj be
GetGlobalObject (). - Perform ?
Set (globalObj, V.[[ReferencedName]], W,false ). - Return
unused .
- If V.[[Strict]] is
- If
IsPropertyReference (V) istrue , then- Let baseObj be ?
ToObject (V.[[Base]]). - If
IsPrivateReference (V) istrue , then- Return ?
PrivateSet (baseObj, V.[[ReferencedName]], W).
- Return ?
- If V.[[ReferencedName]] is not a
property key , then- Set V.[[ReferencedName]] to ?
ToPropertyKey (V.[[ReferencedName]]).
- Set V.[[ReferencedName]] to ?
- Let succeeded be ? baseObj.[[Set]](V.[[ReferencedName]], W,
GetThisValue (V)). - If succeeded is
false and V.[[Strict]] istrue , throw aTypeError exception. - Return
unused .
- Let baseObj be ?
- Else,
- Let base be V.[[Base]].
Assert : base is anEnvironment Record .- Return ? base.SetMutableBinding(V.[[ReferencedName]], W, V.[[Strict]]) (see
9.1 ).
The object that may be created in step
6.2.5.7 GetThisValue ( V )
The abstract operation GetThisValue takes argument V (a
Assert :IsPropertyReference (V) istrue .- If
IsSuperReference (V) istrue , return V.[[ThisValue]]; otherwise return V.[[Base]].
6.2.5.8 InitializeReferencedBinding ( V, W )
The abstract operation InitializeReferencedBinding takes arguments V (a
Assert :IsUnresolvableReference (V) isfalse .- Let base be V.[[Base]].
Assert : base is anEnvironment Record .- Return ? base.InitializeBinding(V.[[ReferencedName]], W).
6.2.5.9 MakePrivateReference ( baseValue, privateIdentifier )
The abstract operation MakePrivateReference takes arguments baseValue (an
- Let privateEnv be the
running execution context 's PrivateEnvironment. Assert : privateEnv is notnull .- Let privateName be
ResolvePrivateIdentifier (privateEnv, privateIdentifier). - Return the
Reference Record { [[Base]]: baseValue, [[ReferencedName]]: privateName, [[Strict]]:true , [[ThisValue]]:empty }.
6.2.6 The Property Descriptor Specification Type
The Property Descriptor type is used to explain the manipulation and reification of Object property attributes. A Property Descriptor is a
Property Descriptor values may be further classified as data Property Descriptors and accessor Property Descriptors based upon the existence or use of certain fields. A data Property Descriptor is one that includes any fields named either [[Value]] or [[Writable]]. An accessor Property Descriptor is one that includes any fields named either [[Get]] or [[Set]]. Any Property Descriptor may have fields named [[Enumerable]] and [[Configurable]]. A Property Descriptor value may not be both a data Property Descriptor and an accessor Property Descriptor; however, it may be neither (in which case it is a generic Property Descriptor). A fully populated Property Descriptor is one that is either an accessor Property Descriptor or a data Property Descriptor and that has all of the corresponding fields defined in
The following
6.2.6.1 IsAccessorDescriptor ( Desc )
The abstract operation IsAccessorDescriptor takes argument Desc (a
- If Desc is
undefined , returnfalse . - If Desc has a [[Get]] field, return
true . - If Desc has a [[Set]] field, return
true . - Return
false .
6.2.6.2 IsDataDescriptor ( Desc )
The abstract operation IsDataDescriptor takes argument Desc (a
- If Desc is
undefined , returnfalse . - If Desc has a [[Value]] field, return
true . - If Desc has a [[Writable]] field, return
true . - Return
false .
6.2.6.3 IsGenericDescriptor ( Desc )
The abstract operation IsGenericDescriptor takes argument Desc (a
- If Desc is
undefined , returnfalse . - If
IsAccessorDescriptor (Desc) istrue , returnfalse . - If
IsDataDescriptor (Desc) istrue , returnfalse . - Return
true .
6.2.6.4 FromPropertyDescriptor ( Desc )
The abstract operation FromPropertyDescriptor takes argument Desc (a
- If Desc is
undefined , returnundefined . - Let obj be
OrdinaryObjectCreate (%Object.prototype% ). Assert : obj is an extensibleordinary object with no own properties.- If Desc has a [[Value]] field, then
- Perform !
CreateDataPropertyOrThrow (obj,"value" , Desc.[[Value]]).
- Perform !
- If Desc has a [[Writable]] field, then
- Perform !
CreateDataPropertyOrThrow (obj,"writable" , Desc.[[Writable]]).
- Perform !
- If Desc has a [[Get]] field, then
- Perform !
CreateDataPropertyOrThrow (obj,"get" , Desc.[[Get]]).
- Perform !
- If Desc has a [[Set]] field, then
- Perform !
CreateDataPropertyOrThrow (obj,"set" , Desc.[[Set]]).
- Perform !
- If Desc has an [[Enumerable]] field, then
- Perform !
CreateDataPropertyOrThrow (obj,"enumerable" , Desc.[[Enumerable]]).
- Perform !
- If Desc has a [[Configurable]] field, then
- Perform !
CreateDataPropertyOrThrow (obj,"configurable" , Desc.[[Configurable]]).
- Perform !
- Return obj.
6.2.6.5 ToPropertyDescriptor ( Obj )
The abstract operation ToPropertyDescriptor takes argument Obj (an
- If Obj
is not an Object , throw aTypeError exception. - Let desc be a new
Property Descriptor that initially has no fields. - Let hasEnumerable be ?
HasProperty (Obj,"enumerable" ). - If hasEnumerable is
true , then - Let hasConfigurable be ?
HasProperty (Obj,"configurable" ). - If hasConfigurable is
true , then - Let hasValue be ?
HasProperty (Obj,"value" ). - If hasValue is
true , then- Let value be ?
Get (Obj,"value" ). - Set desc.[[Value]] to value.
- Let value be ?
- Let hasWritable be ?
HasProperty (Obj,"writable" ). - If hasWritable is
true , then - Let hasGet be ?
HasProperty (Obj,"get" ). - If hasGet is
true , then- Let getter be ?
Get (Obj,"get" ). - If
IsCallable (getter) isfalse and getter is notundefined , throw aTypeError exception. - Set desc.[[Get]] to getter.
- Let getter be ?
- Let hasSet be ?
HasProperty (Obj,"set" ). - If hasSet is
true , then- Let setter be ?
Get (Obj,"set" ). - If
IsCallable (setter) isfalse and setter is notundefined , throw aTypeError exception. - Set desc.[[Set]] to setter.
- Let setter be ?
- If desc has a [[Get]] field or desc has a [[Set]] field, then
- If desc has a [[Value]] field or desc has a [[Writable]] field, throw a
TypeError exception.
- If desc has a [[Value]] field or desc has a [[Writable]] field, throw a
- Return desc.
6.2.6.6 CompletePropertyDescriptor ( Desc )
The abstract operation CompletePropertyDescriptor takes argument Desc (a
- Let like be the
Record { [[Value]]:undefined , [[Writable]]:false , [[Get]]:undefined , [[Set]]:undefined , [[Enumerable]]:false , [[Configurable]]:false }. - If
IsGenericDescriptor (Desc) istrue orIsDataDescriptor (Desc) istrue , then- If Desc does not have a [[Value]] field, set Desc.[[Value]] to like.[[Value]].
- If Desc does not have a [[Writable]] field, set Desc.[[Writable]] to like.[[Writable]].
- Else,
- If Desc does not have a [[Get]] field, set Desc.[[Get]] to like.[[Get]].
- If Desc does not have a [[Set]] field, set Desc.[[Set]] to like.[[Set]].
- If Desc does not have an [[Enumerable]] field, set Desc.[[Enumerable]] to like.[[Enumerable]].
- If Desc does not have a [[Configurable]] field, set Desc.[[Configurable]] to like.[[Configurable]].
- Return
unused .
6.2.7 The Environment Record Specification Type
The
6.2.8 The Abstract Closure Specification Type
The Abstract Closure specification type is used to refer to algorithm steps together with a collection of values. Abstract Closures are meta-values and are invoked using function application style such as closure(arg1, arg2). Like
In algorithm steps that create an Abstract Closure, values are captured with the verb "capture" followed by a list of aliases. When an Abstract Closure is created, it captures the value that is associated with each alias at that time. In steps that specify the algorithm to be performed when an Abstract Closure is called, each captured value is referred to by the alias that was used to capture the value.
If an Abstract Closure returns a
Abstract Closures are created inline as part of other algorithms, shown in the following example.
- Let addend be 41.
- Let closure be a new
Abstract Closure with parameters (x) that captures addend and performs the following steps when called:- Return x + addend.
- Let val be closure(1).
Assert : val is 42.
6.2.9 Data Blocks
The Data Block specification type is used to describe a distinct and mutable sequence of byte-sized (8 bit) numeric values. A byte value is an
For notational convenience within this specification, an array-like syntax can be used to access the individual bytes of a Data Block value. This notation presents a Data Block value as a 0-based
A data block that resides in memory that can be referenced from multiple
The semantics of Shared Data Blocks is defined using
The following
6.2.9.1 CreateByteDataBlock ( size )
The abstract operation CreateByteDataBlock takes argument size (a non-negative
- If size > 253 - 1, throw a
RangeError exception. - Let db be a new
Data Block value consisting of size bytes. If it is impossible to create such aData Block , throw aRangeError exception. - Set all of the bytes of db to 0.
- Return db.
6.2.9.2 CreateSharedByteDataBlock ( size )
The abstract operation CreateSharedByteDataBlock takes argument size (a non-negative
- Let db be a new
Shared Data Block value consisting of size bytes. If it is impossible to create such aShared Data Block , throw aRangeError exception. - Let execution be the [[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - Let eventsRecord be the
Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] isAgentSignifier (). - Let zero be « 0 ».
- For each index i of db, do
- Append
WriteSharedMemory { [[Order]]:init , [[NoTear]]:true , [[Block]]: db, [[ByteIndex]]: i, [[ElementSize]]: 1, [[Payload]]: zero } to eventsRecord.[[EventList]].
- Append
- Return db.
6.2.9.3 CopyDataBlockBytes ( toBlock, toIndex, fromBlock, fromIndex, count )
The abstract operation CopyDataBlockBytes takes arguments toBlock (a
Assert : fromBlock and toBlock are distinct values.- Let fromSize be the number of bytes in fromBlock.
Assert : fromIndex + count ≤ fromSize.- Let toSize be the number of bytes in toBlock.
Assert : toIndex + count ≤ toSize.- Repeat, while count > 0,
- If fromBlock is a
Shared Data Block , then- Let execution be the [[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - Let eventsRecord be the
Agent Events Record of execution.[[EventsRecords]] whose [[AgentSignifier]] isAgentSignifier (). - Let bytes be a
List whose sole element is a nondeterministically chosenbyte value . - NOTE: In implementations, bytes is the result of a non-atomic read instruction on the underlying hardware. The nondeterminism is a semantic prescription of the
memory model to describe observable behaviour of hardware with weak consistency. - Let readEvent be
ReadSharedMemory { [[Order]]:unordered , [[NoTear]]:true , [[Block]]: fromBlock, [[ByteIndex]]: fromIndex, [[ElementSize]]: 1 }. - Append readEvent to eventsRecord.[[EventList]].
- Append
Chosen Value Record { [[Event]]: readEvent, [[ChosenValue]]: bytes } to execution.[[ChosenValues]]. - If toBlock is a
Shared Data Block , then- Append
WriteSharedMemory { [[Order]]:unordered , [[NoTear]]:true , [[Block]]: toBlock, [[ByteIndex]]: toIndex, [[ElementSize]]: 1, [[Payload]]: bytes } to eventsRecord.[[EventList]].
- Append
- Else,
- Set toBlock[toIndex] to bytes[0].
- Let execution be the [[CandidateExecution]] field of the
- Else,
Assert : toBlock is not aShared Data Block .- Set toBlock[toIndex] to fromBlock[fromIndex].
- Set toIndex to toIndex + 1.
- Set fromIndex to fromIndex + 1.
- Set count to count - 1.
- If fromBlock is a
- Return
unused .
6.2.10 The PrivateElement Specification Type
The PrivateElement type is a
Values of the PrivateElement type are
| Field Name | Values of the [[Kind]] field for which it is present | Value | Meaning |
|---|---|---|---|
| [[Key]] | All |
a |
The name of the field, method, or accessor. |
| [[Kind]] | All |
|
The kind of the element. |
| [[Value]] |
|
an |
The value of the field. |
| [[Get]] |
|
a |
The getter for a private accessor. |
| [[Set]] |
|
a |
The setter for a private accessor. |
6.2.11 The ClassFieldDefinition Record Specification Type
The ClassFieldDefinition type is a
Values of the ClassFieldDefinition type are
| Field Name | Value | Meaning |
|---|---|---|
| [[Name]] |
a |
The name of the field. |
| [[Initializer]] |
an ECMAScript |
The initializer of the field, if any. |
6.2.12 Private Names
The Private Name specification type is used to describe a globally unique value (one which differs from any other Private Name, even if they are otherwise indistinguishable) which represents the key of a private class element (field, method, or accessor). Each Private Name has an associated immutable [[Description]] which
6.2.13 The ClassStaticBlockDefinition Record Specification Type
A ClassStaticBlockDefinition Record is a
ClassStaticBlockDefinition Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[BodyFunction]] |
an ECMAScript |
The |
7 Abstract Operations
These operations are not a part of the ECMAScript language; they are defined here solely to aid the specification of the semantics of the ECMAScript language. Other, more specialized
7.1 Type Conversion
The ECMAScript language implicitly performs automatic type conversion as needed. To clarify the semantics of certain constructs it is useful to define a set of conversion
The
7.1.1 ToPrimitive ( input [ , preferredType ] )
The abstract operation ToPrimitive takes argument input (an
- If input
is an Object , then- Let exoticToPrim be ?
GetMethod (input,%Symbol.toPrimitive% ). - If exoticToPrim is not
undefined , then- If preferredType is not present, then
- Let hint be
"default" .
- Let hint be
- Else if preferredType is
string , then- Let hint be
"string" .
- Let hint be
- Else,
Assert : preferredType isnumber .- Let hint be
"number" .
- Let result be ?
Call (exoticToPrim, input, « hint »). - If result
is not an Object , return result. - Throw a
TypeError exception.
- If preferredType is not present, then
- If preferredType is not present, let preferredType be
number . - Return ?
OrdinaryToPrimitive (input, preferredType).
- Let exoticToPrim be ?
- Return input.
When ToPrimitive is called without a hint, then it generally behaves as if the hint were
7.1.1.1 OrdinaryToPrimitive ( O, hint )
The abstract operation OrdinaryToPrimitive takes arguments O (an Object) and hint (
- If hint is
string , then- Let methodNames be «
"toString" ,"valueOf" ».
- Let methodNames be «
- Else,
- Let methodNames be «
"valueOf" ,"toString" ».
- Let methodNames be «
- For each element name of methodNames, do
- Let method be ?
Get (O, name). - If
IsCallable (method) istrue , then- Let result be ?
Call (method, O). - If result
is not an Object , return result.
- Let result be ?
- Let method be ?
- Throw a
TypeError exception.
7.1.2 ToBoolean ( argument )
The abstract operation ToBoolean takes argument argument (an
- If argument
is a Boolean , return argument. - If argument is one of
undefined ,null ,+0 𝔽,-0 𝔽,NaN ,0 ℤ, or the empty String, returnfalse . - NOTE: This step is replaced in section
B.3.6.1 . - Return
true .
7.1.3 ToNumeric ( value )
The abstract operation ToNumeric takes argument value (an
- Let primValue be ?
ToPrimitive (value,number ). - If primValue
is a BigInt , return primValue. - Return ?
ToNumber (primValue).
7.1.4 ToNumber ( argument )
The abstract operation ToNumber takes argument argument (an
- If argument
is a Number , return argument. - If argument is either a Symbol or a BigInt, throw a
TypeError exception. - If argument is
undefined , returnNaN . - If argument is either
null orfalse , return+0 𝔽. - If argument is
true , return1 𝔽. - If argument
is a String , returnStringToNumber (argument). Assert : argumentis an Object .- Let primValue be ?
ToPrimitive (argument,number ). Assert : primValueis not an Object .- Return ?
ToNumber (primValue).
7.1.4.1 ToNumber Applied to the String Type
The abstract operation
Syntax
All grammar symbols not explicitly defined above have the definitions used in the Lexical Grammar for numeric literals (
Some differences should be noted between the syntax of a
-
A
StringNumericLiteral may include leading and/or trailing white space and/or line terminators. -
A
StringNumericLiteral that is decimal may have any number of leading0digits. -
A
StringNumericLiteral that is decimal may include a+or-to indicate its sign. -
A
StringNumericLiteral that is empty or contains only white space is converted to+0 𝔽. -
Infinityand-Infinityare recognized as aStringNumericLiteral but not as aNumericLiteral . -
A
StringNumericLiteral cannot include aBigIntLiteralSuffix . -
A
StringNumericLiteral cannot include aNumericLiteralSeparator .
7.1.4.1.1 StringToNumber ( str )
The abstract operation StringToNumber takes argument str (a String) and returns a Number. It performs the following steps when called:
- Let literal be
ParseText (str,StringNumericLiteral ). - If literal is a
List of errors, returnNaN . - Return the
StringNumericValue of literal.
7.1.4.1.2 Runtime Semantics: StringNumericValue
The
The conversion of a
It is defined piecewise over the following productions:
- Return
+0 𝔽.
- Return the
StringNumericValue ofStrNumericLiteral .
- Return
𝔽 (MV ofNonDecimalIntegerLiteral ).
- Let a be the
StringNumericValue ofStrUnsignedDecimalLiteral . - If a is
+0 𝔽, return-0 𝔽. - Return -a.
- Return
+∞ 𝔽.
- Let a be the MV of the first
DecimalDigits . - If the second
DecimalDigits is present, then- Let b be the MV of the second
DecimalDigits . - Let n be the number of code points in the second
DecimalDigits .
- Let b be the MV of the second
- Else,
- Let b be 0.
- Let n be 0.
- If
ExponentPart is present, let e be the MV ofExponentPart . Otherwise, let e be 0. - Return
RoundMVResult ((a + (b × 10-n)) × 10e).
- Let b be the MV of
DecimalDigits . - If
ExponentPart is present, let e be the MV ofExponentPart . Otherwise, let e be 0. - Let n be the number of code points in
DecimalDigits . - Return
RoundMVResult (b × 10e - n).
- Let a be the MV of
DecimalDigits . - If
ExponentPart is present, let e be the MV ofExponentPart . Otherwise, let e be 0. - Return
RoundMVResult (a × 10e).
7.1.4.1.3 RoundMVResult ( n )
The abstract operation RoundMVResult takes argument n (a
- If the decimal representation of n has 20 or fewer significant digits, return
𝔽 (n). - Let option1 be the
mathematical value denoted by the result of replacing each significant digit in the decimal representation of n after the 20th with a 0 digit. - Let option2 be the
mathematical value denoted by the result of replacing each significant digit in the decimal representation of n after the 20th with a 0 digit and then incrementing it at the 20th position (with carrying as necessary). - Let chosen be an
implementation-defined choice of either option1 or option2. - Return
𝔽 (chosen).
7.1.5 ToIntegerOrInfinity ( argument )
The abstract operation ToIntegerOrInfinity takes argument argument (an
7.1.6 ToInt32 ( argument )
The abstract operation ToInt32 takes argument argument (an
Given the above definition of ToInt32:
- The ToInt32 abstract operation is idempotent: if applied to a result that it produced, the second application leaves that value unchanged.
-
ToInt32(
ToUint32 (x)) is the same value as ToInt32(x) for all values of x. (It is to preserve this latter property that+∞ 𝔽 and-∞ 𝔽 are mapped to+0 𝔽.) -
ToInt32 maps
-0 𝔽 to+0 𝔽.
7.1.7 ToUint32 ( argument )
The abstract operation ToUint32 takes argument argument (an
Given the above definition of ToUint32:
-
Step
5 is the only difference between ToUint32 andToInt32 . - The ToUint32 abstract operation is idempotent: if applied to a result that it produced, the second application leaves that value unchanged.
-
ToUint32(
ToInt32 (x)) is the same value as ToUint32(x) for all values of x. (It is to preserve this latter property that+∞ 𝔽 and-∞ 𝔽 are mapped to+0 𝔽.) -
ToUint32 maps
-0 𝔽 to+0 𝔽.
7.1.8 ToInt16 ( argument )
The abstract operation ToInt16 takes argument argument (an
7.1.9 ToUint16 ( argument )
The abstract operation ToUint16 takes argument argument (an
7.1.10 ToInt8 ( argument )
The abstract operation ToInt8 takes argument argument (an
7.1.11 ToUint8 ( argument )
The abstract operation ToUint8 takes argument argument (an
7.1.12 ToUint8Clamp ( argument )
The abstract operation ToUint8Clamp takes argument argument (an
- Let number be ?
ToNumber (argument). - If number is
NaN , return+0 𝔽. - Let mv be the
extended mathematical value of number. - Let clamped be the result of
clamping mv between 0 and 255. - Let f be
floor (clamped). - If clamped < f + 0.5, return
𝔽 (f). - If clamped > f + 0.5, return
𝔽 (f + 1). - If f is even, return
𝔽 (f). Otherwise, return𝔽 (f + 1).
Unlike most other ECMAScript Math.round
7.1.13 ToBigInt ( argument )
The abstract operation ToBigInt takes argument argument (an
- Let prim be ?
ToPrimitive (argument,number ). - Return the value that prim corresponds to in
Table 12 .
| Argument Type | Result |
|---|---|
| Undefined |
Throw a |
| Null |
Throw a |
| Boolean |
Return 1n if prim is 0n if prim is |
| BigInt | Return prim. |
| Number |
Throw a |
| String |
|
| Symbol |
Throw a |
7.1.14 StringToBigInt ( str )
The abstract operation StringToBigInt takes argument str (a String) and returns a BigInt or
7.1.14.1 StringIntegerLiteral Grammar
Syntax
7.1.14.2 Runtime Semantics: MV
-
The MV of
StringIntegerLiteral ::: StrWhiteSpace opt -
The MV of
StringIntegerLiteral ::: StrWhiteSpace opt StrIntegerLiteral StrWhiteSpace opt StrIntegerLiteral .
7.1.15 ToBigInt64 ( argument )
The abstract operation ToBigInt64 takes argument argument (an
7.1.16 ToBigUint64 ( argument )
The abstract operation ToBigUint64 takes argument argument (an
7.1.17 ToString ( argument )
The abstract operation ToString takes argument argument (an
- If argument
is a String , return argument. - If argument
is a Symbol , throw aTypeError exception. - If argument is
undefined , return"undefined" . - If argument is
null , return"null" . - If argument is
true , return"true" . - If argument is
false , return"false" . - If argument
is a Number , returnNumber::toString (argument, 10). - If argument
is a BigInt , returnBigInt::toString (argument, 10). Assert : argumentis an Object .- Let primValue be ?
ToPrimitive (argument,string ). Assert : primValueis not an Object .- Return ?
ToString (primValue).
7.1.18 ToObject ( argument )
The abstract operation ToObject takes argument argument (an
| Argument Type | Result |
|---|---|
| Undefined |
Throw a |
| Null |
Throw a |
| Boolean |
Return a new Boolean object whose [[BooleanData]] internal slot is set to argument. See |
| Number |
Return a new Number object whose [[NumberData]] internal slot is set to argument. See |
| String |
Return a new String object whose [[StringData]] internal slot is set to argument. See |
| Symbol |
Return a new Symbol object whose [[SymbolData]] internal slot is set to argument. See |
| BigInt |
Return a new BigInt object whose [[BigIntData]] internal slot is set to argument. See |
| Object | Return argument. |
7.1.19 ToPropertyKey ( argument )
The abstract operation ToPropertyKey takes argument argument (an
- Let key be ?
ToPrimitive (argument,string ). - If key
is a Symbol , then- Return key.
- Return !
ToString (key).
7.1.20 ToLength ( argument )
The abstract operation ToLength takes argument argument (an
- Let len be ?
ToIntegerOrInfinity (argument). - If len ≤ 0, return
+0 𝔽. - Return
𝔽 (min (len, 253 - 1)).
7.1.21 CanonicalNumericIndexString ( argument )
The abstract operation CanonicalNumericIndexString takes argument argument (a String) and returns a Number or
A canonical numeric string is any String value for which the CanonicalNumericIndexString abstract operation does not return
7.1.22 ToIndex ( value )
The abstract operation ToIndex takes argument value (an
- Let integer be ?
ToIntegerOrInfinity (value). - If integer is not in the
inclusive interval from 0 to 253 - 1, throw aRangeError exception. - Return integer.
7.2 Testing and Comparison Operations
7.2.1 RequireObjectCoercible ( argument )
The abstract operation RequireObjectCoercible takes argument argument (an
| Argument Type | Result |
|---|---|
| Undefined |
Throw a |
| Null |
Throw a |
| Boolean | Return argument. |
| Number | Return argument. |
| String | Return argument. |
| Symbol | Return argument. |
| BigInt | Return argument. |
| Object | Return argument. |
7.2.2 IsArray ( argument )
The abstract operation IsArray takes argument argument (an
- If argument
is not an Object , returnfalse . - If argument is an
Array exotic object , returntrue . - If argument is a
Proxy exotic object , then- Perform ?
ValidateNonRevokedProxy (argument). - Let proxyTarget be argument.[[ProxyTarget]].
- Return ?
IsArray (proxyTarget).
- Perform ?
- Return
false .
7.2.3 IsCallable ( argument )
The abstract operation IsCallable takes argument argument (an
- If argument
is not an Object , returnfalse . - If argument has a [[Call]] internal method, return
true . - Return
false .
7.2.4 IsConstructor ( argument )
The abstract operation IsConstructor takes argument argument (an
- If argument
is not an Object , returnfalse . - If argument has a [[Construct]] internal method, return
true . - Return
false .
7.2.5 IsExtensible ( O )
The abstract operation IsExtensible takes argument O (an Object) and returns either a
- Return ? O.[[IsExtensible]]().
7.2.6 IsRegExp ( argument )
The abstract operation IsRegExp takes argument argument (an
- If argument
is not an Object , returnfalse . - Let matcher be ?
Get (argument,%Symbol.match% ). - If matcher is not
undefined , returnToBoolean (matcher). - If argument has a [[RegExpMatcher]] internal slot, return
true . - Return
false .
7.2.7 Static Semantics: IsStringWellFormedUnicode ( string )
The abstract operation IsStringWellFormedUnicode takes argument string (a String) and returns a Boolean. It interprets string as a sequence of UTF-16 encoded code points, as described in
- Let len be the length of string.
- Let k be 0.
- Repeat, while k < len,
- Let cp be
CodePointAt (string, k). - If cp.[[IsUnpairedSurrogate]] is
true , returnfalse . - Set k to k + cp.[[CodeUnitCount]].
- Let cp be
- Return
true .
7.2.8 SameType ( x, y )
The abstract operation SameType takes arguments x (an
- If x is
undefined and y isundefined , returntrue . - If x is
null and y isnull , returntrue . - If x
is a Boolean and yis a Boolean , returntrue . - If x
is a Number and yis a Number , returntrue . - If x
is a BigInt and yis a BigInt , returntrue . - If x
is a Symbol and yis a Symbol , returntrue . - If x
is a String and yis a String , returntrue . - If x
is an Object and yis an Object , returntrue . - Return
false .
7.2.9 SameValue ( x, y )
The abstract operation SameValue takes arguments x (an
- If
SameType (x, y) isfalse , returnfalse . - If x
is a Number , then- Return
Number::sameValue (x, y).
- Return
- Return
SameValueNonNumber (x, y).
This algorithm differs from the
7.2.10 SameValueZero ( x, y )
The abstract operation SameValueZero takes arguments x (an
- If
SameType (x, y) isfalse , returnfalse . - If x
is a Number , then- Return
Number::sameValueZero (x, y).
- Return
- Return
SameValueNonNumber (x, y).
SameValueZero differs from
7.2.11 SameValueNonNumber ( x, y )
The abstract operation SameValueNonNumber takes arguments x (an
Assert :SameType (x, y) istrue .- If x is either
null orundefined , returntrue . - If x
is a BigInt , then- Return
BigInt::equal (x, y).
- Return
- If x
is a String , then- If x and y have the same length and the same code units in the same positions, return
true ; otherwise, returnfalse .
- If x and y have the same length and the same code units in the same positions, return
- If x
is a Boolean , then- If x and y are both
true or bothfalse , returntrue ; otherwise, returnfalse .
- If x and y are both
- NOTE: All other
ECMAScript language values are compared by identity. - If x is y, return
true ; otherwise, returnfalse .
7.2.12 IsLessThan ( x, y, LeftFirst )
The abstract operation IsLessThan takes arguments x (an
- If LeftFirst is
true , then- Let px be ?
ToPrimitive (x,number ). - Let py be ?
ToPrimitive (y,number ).
- Let px be ?
- Else,
- NOTE: The order of evaluation needs to be reversed to preserve left to right evaluation.
- Let py be ?
ToPrimitive (y,number ). - Let px be ?
ToPrimitive (x,number ).
- If px
is a String and pyis a String , then- Let lx be the length of px.
- Let ly be the length of py.
- For each
integer i such that 0 ≤ i <min (lx, ly), in ascending order, do- Let cx be the numeric value of the code unit at index i within px.
- Let cy be the numeric value of the code unit at index i within py.
- If cx < cy, return
true . - If cx > cy, return
false .
- If lx < ly, return
true . Otherwise, returnfalse .
- Else,
- If px
is a BigInt and pyis a String , then- Let ny be
StringToBigInt (py). - If ny is
undefined , returnundefined . - Return
BigInt::lessThan (px, ny).
- Let ny be
- If px
is a String and pyis a BigInt , then- Let nx be
StringToBigInt (px). - If nx is
undefined , returnundefined . - Return
BigInt::lessThan (nx, py).
- Let nx be
- NOTE: Because px and py are primitive values, evaluation order is not important.
- Let nx be ?
ToNumeric (px). - Let ny be ?
ToNumeric (py). - If
SameType (nx, ny) istrue , then- If nx
is a Number , then- Return
Number::lessThan (nx, ny).
- Return
- Else,
Assert : nxis a BigInt .- Return
BigInt::lessThan (nx, ny).
- If nx
Assert : nxis a BigInt and nyis a Number , or nxis a Number and nyis a BigInt .- If nx or ny is
NaN , returnundefined . - If nx is
-∞ 𝔽 or ny is+∞ 𝔽, returntrue . - If nx is
+∞ 𝔽 or ny is-∞ 𝔽, returnfalse . - If
ℝ (nx) <ℝ (ny), returntrue ; otherwise returnfalse .
- If px
The comparison of Strings uses a simple lexicographic ordering on sequences of UTF-16 code unit values. There is no attempt to use the more complex, semantically oriented definitions of character or string equality and collating order defined in the Unicode specification. Therefore String values that are canonically equal according to the Unicode Standard but not in the same normalization form could test as unequal. Also note that lexicographic ordering by code unit differs from ordering by code point for Strings containing
7.2.13 IsLooselyEqual ( x, y )
The abstract operation IsLooselyEqual takes arguments x (an == operator. It performs the following steps when called:
- If
SameType (x, y) istrue , then- Return
IsStrictlyEqual (x, y).
- Return
- If x is
null and y isundefined , returntrue . - If x is
undefined and y isnull , returntrue . - NOTE: This step is replaced in section
B.3.6.2 . - If x
is a Number and yis a String , return !IsLooselyEqual (x, !ToNumber (y)). - If x
is a String and yis a Number , return !IsLooselyEqual (!ToNumber (x), y). - If x
is a BigInt and yis a String , then- Let n be
StringToBigInt (y). - If n is
undefined , returnfalse . - Return !
IsLooselyEqual (x, n).
- Let n be
- If x
is a String and yis a BigInt , return !IsLooselyEqual (y, x). - If x
is a Boolean , return !IsLooselyEqual (!ToNumber (x), y). - If y
is a Boolean , return !IsLooselyEqual (x, !ToNumber (y)). - If x is either a String, a Number, a BigInt, or a Symbol and y
is an Object , return !IsLooselyEqual (x, ?ToPrimitive (y)). - If x
is an Object and y is either a String, a Number, a BigInt, or a Symbol, return !IsLooselyEqual (?ToPrimitive (x), y). - If x
is a BigInt and yis a Number , or if xis a Number and yis a BigInt , then - Return
false .
7.2.14 IsStrictlyEqual ( x, y )
The abstract operation IsStrictlyEqual takes arguments x (an === operator. It performs the following steps when called:
- If
SameType (x, y) isfalse , returnfalse . - If x
is a Number , then- Return
Number::equal (x, y).
- Return
- Return
SameValueNonNumber (x, y).
This algorithm differs from the
7.3 Operations on Objects
7.3.1 MakeBasicObject ( internalSlotsList )
The abstract operation MakeBasicObject takes argument internalSlotsList (a
- Set internalSlotsList to the
list-concatenation of internalSlotsList and « [[PrivateElements]] ». - Let obj be a newly created object with an internal slot for each name in internalSlotsList.
- NOTE: As described in
Object Internal Methods and Internal Slots , the initial value of each such internal slot isundefined unless specified otherwise. - Set obj.[[PrivateElements]] to a new empty
List . - Set obj's essential internal methods to the default
ordinary object definitions specified in10.1 . Assert : If the caller will not be overriding both obj's [[GetPrototypeOf]] and [[SetPrototypeOf]] essential internal methods, then internalSlotsList contains [[Prototype]].Assert : If the caller will not be overriding all of obj's [[SetPrototypeOf]], [[IsExtensible]], and [[PreventExtensions]] essential internal methods, then internalSlotsList contains [[Extensible]].- If internalSlotsList contains [[Extensible]], set obj.[[Extensible]] to
true . - Return obj.
Within this specification,
7.3.2 Get ( O, P )
The abstract operation Get takes arguments O (an Object) and P (a
- Return ? O.[[Get]](P, O).
7.3.3 GetV ( V, P )
The abstract operation GetV takes arguments V (an
- Let O be ?
ToObject (V). - Return ? O.[[Get]](P, V).
7.3.4 Set ( O, P, V, Throw )
The abstract operation Set takes arguments O (an Object), P (a
- Let success be ? O.[[Set]](P, V, O).
- If success is
false and Throw istrue , throw aTypeError exception. - Return
unused .
7.3.5 CreateDataProperty ( O, P, V )
The abstract operation CreateDataProperty takes arguments O (an Object), P (a
- Let newDesc be the PropertyDescriptor { [[Value]]: V, [[Writable]]:
true , [[Enumerable]]:true , [[Configurable]]:true }. - Return ? O.[[DefineOwnProperty]](P, newDesc).
This abstract operation creates a property whose attributes are set to the same defaults used for properties created by the ECMAScript language assignment operator. Normally, the property will not already exist. If it does exist and is not configurable or if O is not extensible, [[DefineOwnProperty]] will return
7.3.6 CreateDataPropertyOrThrow ( O, P, V )
The abstract operation CreateDataPropertyOrThrow takes arguments O (an Object), P (a
- Let success be ?
CreateDataProperty (O, P, V). - If success is
false , throw aTypeError exception. - Return
unused .
This abstract operation creates a property whose attributes are set to the same defaults used for properties created by the ECMAScript language assignment operator. Normally, the property will not already exist. If it does exist and is not configurable or if O is not extensible, [[DefineOwnProperty]] will return
7.3.7 CreateNonEnumerableDataPropertyOrThrow ( O, P, V )
The abstract operation CreateNonEnumerableDataPropertyOrThrow takes arguments O (an Object), P (a
Assert : O is an ordinary, extensible object with no non-configurable properties.- Let newDesc be the PropertyDescriptor { [[Value]]: V, [[Writable]]:
true , [[Enumerable]]:false , [[Configurable]]:true }. - Perform !
DefinePropertyOrThrow (O, P, newDesc). - Return
unused .
This abstract operation creates a property whose attributes are set to the same defaults used for properties created by the ECMAScript language assignment operator except it is not enumerable. Normally, the property will not already exist. If it does exist,
7.3.8 DefinePropertyOrThrow ( O, P, desc )
The abstract operation DefinePropertyOrThrow takes arguments O (an Object), P (a
- Let success be ? O.[[DefineOwnProperty]](P, desc).
- If success is
false , throw aTypeError exception. - Return
unused .
7.3.9 DeletePropertyOrThrow ( O, P )
The abstract operation DeletePropertyOrThrow takes arguments O (an Object) and P (a
- Let success be ? O.[[Delete]](P).
- If success is
false , throw aTypeError exception. - Return
unused .
7.3.10 GetMethod ( V, P )
The abstract operation GetMethod takes arguments V (an
- Let func be ?
GetV (V, P). - If func is either
undefined ornull , returnundefined . - If
IsCallable (func) isfalse , throw aTypeError exception. - Return func.
7.3.11 HasProperty ( O, P )
The abstract operation HasProperty takes arguments O (an Object) and P (a
- Return ? O.[[HasProperty]](P).
7.3.12 HasOwnProperty ( O, P )
The abstract operation HasOwnProperty takes arguments O (an Object) and P (a
- Let desc be ? O.[[GetOwnProperty]](P).
- If desc is
undefined , returnfalse . - Return
true .
7.3.13 Call ( F, V [ , argumentsList ] )
The abstract operation Call takes arguments F (an
- If argumentsList is not present, set argumentsList to a new empty
List . - If
IsCallable (F) isfalse , throw aTypeError exception. - Return ? F.[[Call]](V, argumentsList).
7.3.14 Construct ( F [ , argumentsList [ , newTarget ] ] )
The abstract operation Construct takes argument F (a
- If newTarget is not present, set newTarget to F.
- If argumentsList is not present, set argumentsList to a new empty
List . - Return ? F.[[Construct]](argumentsList, newTarget).
If newTarget is not present, this operation is equivalent to: new F(...argumentsList)
7.3.15 SetIntegrityLevel ( O, level )
The abstract operation SetIntegrityLevel takes arguments O (an Object) and level (
- Let status be ? O.[[PreventExtensions]]().
- If status is
false , returnfalse . - Let keys be ? O.[[OwnPropertyKeys]]().
- If level is
sealed , then- For each element k of keys, do
- Perform ?
DefinePropertyOrThrow (O, k, PropertyDescriptor { [[Configurable]]:false }).
- Perform ?
- For each element k of keys, do
- Else,
Assert : level isfrozen .- For each element k of keys, do
- Let currentDesc be ? O.[[GetOwnProperty]](k).
- If currentDesc is not
undefined , then- If
IsAccessorDescriptor (currentDesc) istrue , then- Let desc be the PropertyDescriptor { [[Configurable]]:
false }.
- Let desc be the PropertyDescriptor { [[Configurable]]:
- Else,
- Let desc be the PropertyDescriptor { [[Configurable]]:
false , [[Writable]]:false }.
- Let desc be the PropertyDescriptor { [[Configurable]]:
- Perform ?
DefinePropertyOrThrow (O, k, desc).
- If
- Return
true .
7.3.16 TestIntegrityLevel ( O, level )
The abstract operation TestIntegrityLevel takes arguments O (an Object) and level (
- Let extensible be ?
IsExtensible (O). - If extensible is
true , returnfalse . - NOTE: If the object is extensible, none of its properties are examined.
- Let keys be ? O.[[OwnPropertyKeys]]().
- For each element k of keys, do
- Let currentDesc be ? O.[[GetOwnProperty]](k).
- If currentDesc is not
undefined , then- If currentDesc.[[Configurable]] is
true , returnfalse . - If level is
frozen andIsDataDescriptor (currentDesc) istrue , then- If currentDesc.[[Writable]] is
true , returnfalse .
- If currentDesc.[[Writable]] is
- If currentDesc.[[Configurable]] is
- Return
true .
7.3.17 CreateArrayFromList ( elements )
The abstract operation CreateArrayFromList takes argument elements (a
- Let array be !
ArrayCreate (0). - Let n be 0.
- For each element e of elements, do
- Perform !
CreateDataPropertyOrThrow (array, !ToString (𝔽 (n)), e). - Set n to n + 1.
- Perform !
- Return array.
7.3.18 LengthOfArrayLike ( obj )
The abstract operation LengthOfArrayLike takes argument obj (an Object) and returns either a
An array-like object is any object for which this operation returns a
7.3.19 CreateListFromArrayLike ( obj [ , validElementTypes ] )
The abstract operation CreateListFromArrayLike takes argument obj (an
- If validElementTypes is not present, set validElementTypes to
all . - If obj
is not an Object , throw aTypeError exception. - Let len be ?
LengthOfArrayLike (obj). - Let list be a new empty
List . - Let index be 0.
- Repeat, while index < len,
- Let indexName be !
ToString (𝔽 (index)). - Let next be ?
Get (obj, indexName). - If validElementTypes is
property-key and next is not aproperty key , throw aTypeError exception. - Append next to list.
- Set index to index + 1.
- Let indexName be !
- Return list.
7.3.20 Invoke ( V, P [ , argumentsList ] )
The abstract operation Invoke takes arguments V (an
7.3.21 OrdinaryHasInstance ( C, O )
The abstract operation OrdinaryHasInstance takes arguments C (an
- If
IsCallable (C) isfalse , returnfalse . - If C has a [[BoundTargetFunction]] internal slot, then
- Let BC be C.[[BoundTargetFunction]].
- Return ?
InstanceofOperator (O, BC).
- If O
is not an Object , returnfalse . - Let P be ?
Get (C,"prototype" ). - If P
is not an Object , throw aTypeError exception. - Repeat,
- Set O to ? O.[[GetPrototypeOf]]().
- If O is
null , returnfalse . - If
SameValue (P, O) istrue , returntrue .
7.3.22 SpeciesConstructor ( O, defaultConstructor )
The abstract operation SpeciesConstructor takes arguments O (an Object) and defaultConstructor (a
- Let C be ?
Get (O,"constructor" ). - If C is
undefined , return defaultConstructor. - If C
is not an Object , throw aTypeError exception. - Let S be ?
Get (C,%Symbol.species% ). - If S is either
undefined ornull , return defaultConstructor. - If
IsConstructor (S) istrue , return S. - Throw a
TypeError exception.
7.3.23 EnumerableOwnProperties ( O, kind )
The abstract operation EnumerableOwnProperties takes arguments O (an Object) and kind (
- Let ownKeys be ? O.[[OwnPropertyKeys]]().
- Let results be a new empty
List . - For each element key of ownKeys, do
- If key
is a String , then- Let desc be ? O.[[GetOwnProperty]](key).
- If desc is not
undefined and desc.[[Enumerable]] istrue , then- If kind is
key , then- Append key to results.
- Else,
- Let value be ?
Get (O, key). - If kind is
value , then- Append value to results.
- Else,
Assert : kind iskey+value .- Let entry be
CreateArrayFromList (« key, value »). - Append entry to results.
- Let value be ?
- If kind is
- If key
- Return results.
7.3.24 GetFunctionRealm ( obj )
The abstract operation GetFunctionRealm takes argument obj (a
- If obj has a [[Realm]] internal slot, then
- Return obj.[[Realm]].
- If obj is a
bound function exotic object , then- Let boundTargetFunction be obj.[[BoundTargetFunction]].
- Return ?
GetFunctionRealm (boundTargetFunction).
- If obj is a
Proxy exotic object , then- Perform ?
ValidateNonRevokedProxy (obj). - Let proxyTarget be obj.[[ProxyTarget]].
Assert : proxyTarget is afunction object .- Return ?
GetFunctionRealm (proxyTarget).
- Perform ?
- Return
the current Realm Record .
Step
7.3.25 CopyDataProperties ( target, source, excludedItems )
The abstract operation CopyDataProperties takes arguments target (an Object), source (an
- If source is either
undefined ornull , returnunused . - Let from be !
ToObject (source). - Let keys be ? from.[[OwnPropertyKeys]]().
- For each element nextKey of keys, do
- Let excluded be
false . - For each element e of excludedItems, do
- If
SameValue (e, nextKey) istrue , then- Set excluded to
true .
- Set excluded to
- If
- If excluded is
false , then- Let desc be ? from.[[GetOwnProperty]](nextKey).
- If desc is not
undefined and desc.[[Enumerable]] istrue , then- Let propValue be ?
Get (from, nextKey). - Perform !
CreateDataPropertyOrThrow (target, nextKey, propValue).
- Let propValue be ?
- Let excluded be
- Return
unused .
The target passed in here is always a newly created object which is not directly accessible in case of an error being thrown.
7.3.26 PrivateElementFind ( O, P )
The abstract operation PrivateElementFind takes arguments O (an Object) and P (a
- If O.[[PrivateElements]] contains a
PrivateElement pe such that pe.[[Key]] is P, then- Return pe.
- Return
empty .
7.3.27 PrivateFieldAdd ( O, P, value )
The abstract operation PrivateFieldAdd takes arguments O (an Object), P (a
- If the
host is a web browser, then- Perform ?
HostEnsureCanAddPrivateElement (O).
- Perform ?
- Let entry be
PrivateElementFind (O, P). - If entry is not
empty , throw aTypeError exception. - Append
PrivateElement { [[Key]]: P, [[Kind]]:field , [[Value]]: value } to O.[[PrivateElements]]. - Return
unused .
7.3.28 PrivateMethodOrAccessorAdd ( O, method )
The abstract operation PrivateMethodOrAccessorAdd takes arguments O (an Object) and method (a
Assert : method.[[Kind]] is eithermethod oraccessor .- If the
host is a web browser, then- Perform ?
HostEnsureCanAddPrivateElement (O).
- Perform ?
- Let entry be
PrivateElementFind (O, method.[[Key]]). - If entry is not
empty , throw aTypeError exception. - Append method to O.[[PrivateElements]].
- Return
unused .
The values for private methods and accessors are shared across instances. This operation does not create a new copy of the method or accessor.
7.3.29 HostEnsureCanAddPrivateElement ( O )
The
An implementation of HostEnsureCanAddPrivateElement must conform to the following requirements:
- If O is not a
host-defined exotic object , this abstract operation must returnNormalCompletion (unused ) and perform no other steps. - Any two calls of this abstract operation with the same argument must return the same kind of
Completion Record .
The default implementation of HostEnsureCanAddPrivateElement is to return
This abstract operation is only invoked by ECMAScript
7.3.30 PrivateGet ( O, P )
The abstract operation PrivateGet takes arguments O (an Object) and P (a
- Let entry be
PrivateElementFind (O, P). - If entry is
empty , throw aTypeError exception. - If entry.[[Kind]] is either
field ormethod , then- Return entry.[[Value]].
Assert : entry.[[Kind]] isaccessor .- If entry.[[Get]] is
undefined , throw aTypeError exception. - Let getter be entry.[[Get]].
- Return ?
Call (getter, O).
7.3.31 PrivateSet ( O, P, value )
The abstract operation PrivateSet takes arguments O (an Object), P (a
- Let entry be
PrivateElementFind (O, P). - If entry is
empty , throw aTypeError exception. - If entry.[[Kind]] is
field , then- Set entry.[[Value]] to value.
- Else if entry.[[Kind]] is
method , then- Throw a
TypeError exception.
- Throw a
- Else,
- Return
unused .
7.3.32 DefineField ( receiver, fieldRecord )
The abstract operation DefineField takes arguments receiver (an Object) and fieldRecord (a
- Let fieldName be fieldRecord.[[Name]].
- Let initializer be fieldRecord.[[Initializer]].
- If initializer is not
empty , then- Let initValue be ?
Call (initializer, receiver).
- Let initValue be ?
- Else,
- Let initValue be
undefined .
- Let initValue be
- If fieldName is a
Private Name , then- Perform ?
PrivateFieldAdd (receiver, fieldName, initValue).
- Perform ?
- Else,
Assert : fieldName is aproperty key .- Perform ?
CreateDataPropertyOrThrow (receiver, fieldName, initValue).
- Return
unused .
7.3.33 InitializeInstanceElements ( O, constructor )
The abstract operation InitializeInstanceElements takes arguments O (an Object) and constructor (an ECMAScript
- Let methods be the value of constructor.[[PrivateMethods]].
- For each
PrivateElement method of methods, do- Perform ?
PrivateMethodOrAccessorAdd (O, method).
- Perform ?
- Let fields be the value of constructor.[[Fields]].
- For each element fieldRecord of fields, do
- Perform ?
DefineField (O, fieldRecord).
- Perform ?
- Return
unused .
7.3.34 AddValueToKeyedGroup ( groups, key, value )
The abstract operation AddValueToKeyedGroup takes arguments groups (a
7.3.35 GroupBy ( items, callback, keyCoercion )
The abstract operation GroupBy takes arguments items (an
- Perform ?
RequireObjectCoercible (items). - If
IsCallable (callback) isfalse , throw aTypeError exception. - Let groups be a new empty
List . - Let iteratorRecord be ?
GetIterator (items,sync ). - Let k be 0.
- Repeat,
- If k ≥ 253 - 1, then
- Let error be
ThrowCompletion (a newly createdTypeError object). - Return ?
IteratorClose (iteratorRecord, error).
- Let error be
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , then- Return groups.
- Let value be next.
- Let key be
Completion (Call (callback,undefined , « value,𝔽 (k) »)). IfAbruptCloseIterator (key, iteratorRecord).- If keyCoercion is
property , then- Set key to
Completion (ToPropertyKey (key)). IfAbruptCloseIterator (key, iteratorRecord).
- Set key to
- Else,
Assert : keyCoercion iscollection .- Set key to
CanonicalizeKeyedCollectionKey (key).
- Perform
AddValueToKeyedGroup (groups, key, value). - Set k to k + 1.
- If k ≥ 253 - 1, then
7.3.36 SetterThatIgnoresPrototypeProperties ( thisValue, home, p, v )
The abstract operation SetterThatIgnoresPrototypeProperties takes arguments thisValue (an
- If thisValue
is not an Object , then- Throw a
TypeError exception.
- Throw a
- If
SameValue (thisValue, home) istrue , then- NOTE: Throwing here emulates assignment to a non-writable
data property on the home object instrict mode code . - Throw a
TypeError exception.
- NOTE: Throwing here emulates assignment to a non-writable
- Let desc be ? thisValue.[[GetOwnProperty]](p).
- If desc is
undefined , then- Perform ?
CreateDataPropertyOrThrow (thisValue, p, v).
- Perform ?
- Else,
- Perform ?
Set (thisValue, p, v,true ).
- Perform ?
- Return
unused .
7.4 Operations on Iterator Objects
See Common Iteration Interfaces (
7.4.1 Iterator Records
An Iterator Record is a next method.
Iterator Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Iterator]] | an Object |
An object that conforms to the |
| [[NextMethod]] |
an |
The next method of the [[Iterator]] object.
|
| [[Done]] | a Boolean |
Whether the |
7.4.2 GetIteratorDirect ( obj )
The abstract operation GetIteratorDirect takes argument obj (an Object) and returns either a
- Let nextMethod be ?
Get (obj,"next" ). - Let iteratorRecord be the
Iterator Record { [[Iterator]]: obj, [[NextMethod]]: nextMethod, [[Done]]:false }. - Return iteratorRecord.
7.4.3 GetIteratorFromMethod ( obj, method )
The abstract operation GetIteratorFromMethod takes arguments obj (an
- Let iterator be ?
Call (method, obj). - If iterator
is not an Object , throw aTypeError exception. - Return ?
GetIteratorDirect (iterator).
7.4.4 GetIterator ( obj, kind )
The abstract operation GetIterator takes arguments obj (an
- If kind is
async , then- Let method be ?
GetMethod (obj,%Symbol.asyncIterator% ). - If method is
undefined , then- Let syncMethod be ?
GetMethod (obj,%Symbol.iterator% ). - If syncMethod is
undefined , throw aTypeError exception. - Let syncIteratorRecord be ?
GetIteratorFromMethod (obj, syncMethod). - Return
CreateAsyncFromSyncIterator (syncIteratorRecord).
- Let syncMethod be ?
- Let method be ?
- Else,
- Let method be ?
GetMethod (obj,%Symbol.iterator% ).
- Let method be ?
- If method is
undefined , throw aTypeError exception. - Return ?
GetIteratorFromMethod (obj, method).
7.4.5 GetIteratorFlattenable ( obj, primitiveHandling )
The abstract operation GetIteratorFlattenable takes arguments obj (an
- If obj
is not an Object , then- If primitiveHandling is
reject-primitives , throw aTypeError exception. Assert : primitiveHandling isiterate-string-primitives .- If obj
is not a String , throw aTypeError exception.
- If primitiveHandling is
- Let method be ?
GetMethod (obj,%Symbol.iterator% ). - If method is
undefined , then- Let iterator be obj.
- Else,
- Let iterator be ?
Call (method, obj).
- Let iterator be ?
- If iterator
is not an Object , throw aTypeError exception. - Return ?
GetIteratorDirect (iterator).
7.4.6 IteratorNext ( iteratorRecord [ , value ] )
The abstract operation IteratorNext takes argument iteratorRecord (an
- If value is not present, then
- Let result be
Completion (Call (iteratorRecord.[[NextMethod]], iteratorRecord.[[Iterator]])).
- Let result be
- Else,
- Let result be
Completion (Call (iteratorRecord.[[NextMethod]], iteratorRecord.[[Iterator]], « value »)).
- Let result be
- If result is a
throw completion , then- Set iteratorRecord.[[Done]] to
true . - Return ? result.
- Set iteratorRecord.[[Done]] to
- Set result to ! result.
- If result
is not an Object , then- Set iteratorRecord.[[Done]] to
true . - Throw a
TypeError exception.
- Set iteratorRecord.[[Done]] to
- Return result.
7.4.7 IteratorComplete ( iteratorResult )
The abstract operation IteratorComplete takes argument iteratorResult (an Object) and returns either a
7.4.8 IteratorValue ( iteratorResult )
The abstract operation IteratorValue takes argument iteratorResult (an Object) and returns either a
- Return ?
Get (iteratorResult,"value" ).
7.4.9 IteratorStep ( iteratorRecord )
The abstract operation IteratorStep takes argument iteratorRecord (an
- Let result be ?
IteratorNext (iteratorRecord). - Let done be
Completion (IteratorComplete (result)). - If done is a
throw completion , then- Set iteratorRecord.[[Done]] to
true . - Return ? done.
- Set iteratorRecord.[[Done]] to
- Set done to ! done.
- If done is
true , then- Set iteratorRecord.[[Done]] to
true . - Return
done .
- Set iteratorRecord.[[Done]] to
- Return result.
7.4.10 IteratorStepValue ( iteratorRecord )
The abstract operation IteratorStepValue takes argument iteratorRecord (an
- Let result be ?
IteratorStep (iteratorRecord). - If result is
done , then- Return
done .
- Return
- Let value be
Completion (IteratorValue (result)). - If value is a
throw completion , then- Set iteratorRecord.[[Done]] to
true .
- Set iteratorRecord.[[Done]] to
- Return ? value.
7.4.11 IteratorClose ( iteratorRecord, completion )
The abstract operation IteratorClose takes arguments iteratorRecord (an
Assert : iteratorRecord.[[Iterator]]is an Object .- Let iterator be iteratorRecord.[[Iterator]].
- Let innerResult be
Completion (GetMethod (iterator,"return" )). - If innerResult is a
normal completion , then- Let return be innerResult.[[Value]].
- If return is
undefined , return ? completion. - Set innerResult to
Completion (Call (return, iterator)).
- If completion is a
throw completion , return ? completion. - If innerResult is a
throw completion , return ? innerResult. - If innerResult.[[Value]]
is not an Object , throw aTypeError exception. - Return ? completion.
7.4.12 IfAbruptCloseIterator ( value, iteratorRecord )
IfAbruptCloseIterator is a shorthand for a sequence of algorithm steps that use an
IfAbruptCloseIterator (value, iteratorRecord).
means the same thing as:
Assert : value is aCompletion Record .- If value is an
abrupt completion , return ?IteratorClose (iteratorRecord, value). - Else, set value to ! value.
7.4.13 AsyncIteratorClose ( iteratorRecord, completion )
The abstract operation AsyncIteratorClose takes arguments iteratorRecord (an
Assert : iteratorRecord.[[Iterator]]is an Object .- Let iterator be iteratorRecord.[[Iterator]].
- Let innerResult be
Completion (GetMethod (iterator,"return" )). - If innerResult is a
normal completion , then- Let return be innerResult.[[Value]].
- If return is
undefined , return ? completion. - Set innerResult to
Completion (Call (return, iterator)). - If innerResult is a
normal completion , set innerResult toCompletion (Await (innerResult.[[Value]])).
- If completion is a
throw completion , return ? completion. - If innerResult is a
throw completion , return ? innerResult. - If innerResult.[[Value]]
is not an Object , throw aTypeError exception. - Return ? completion.
7.4.14 CreateIteratorResultObject ( value, done )
The abstract operation CreateIteratorResultObject takes arguments value (an
- Let obj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (obj,"value" , value). - Perform !
CreateDataPropertyOrThrow (obj,"done" , done). - Return obj.
7.4.15 CreateListIteratorRecord ( list )
The abstract operation CreateListIteratorRecord takes argument list (a
- Let closure be a new
Abstract Closure with no parameters that captures list and performs the following steps when called:- For each element E of list, do
- Perform ?
GeneratorYield (CreateIteratorResultObject (E,false )).
- Perform ?
- Return
NormalCompletion (undefined ).
- For each element E of list, do
- Let iterator be
CreateIteratorFromClosure (closure,empty ,%Iterator.prototype% ). - Return the
Iterator Record { [[Iterator]]: iterator, [[NextMethod]]: %GeneratorPrototype.next%, [[Done]]:false }.
The list
7.4.16 IteratorToList ( iteratorRecord )
The abstract operation IteratorToList takes argument iteratorRecord (an
- Let values be a new empty
List . - Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , then- Return values.
- Append next to values.
- Let next be ?
8 Syntax-Directed Operations
In addition to those defined in this section, specialized
8.1 Runtime Semantics: Evaluation
The
8.2 Scope Analysis
8.2.1 Static Semantics: BoundNames
The
It is defined piecewise over the following productions:
- Return a
List whose sole element is theStringValue ofIdentifier .
- Return «
"yield" ».
- Return «
"await" ».
- Return the
BoundNames ofBindingList .
- Let names1 be the
BoundNames ofBindingList . - Let names2 be the
BoundNames ofLexicalBinding . - Return the
list-concatenation of names1 and names2.
- Return the
BoundNames ofBindingIdentifier .
- Return the
BoundNames ofBindingPattern .
- Let names1 be the
BoundNames ofVariableDeclarationList . - Let names2 be the
BoundNames ofVariableDeclaration . - Return the
list-concatenation of names1 and names2.
- Return the
BoundNames ofBindingIdentifier .
- Return the
BoundNames ofBindingPattern .
- Return a new empty
List .
- Let names1 be the
BoundNames ofBindingPropertyList . - Let names2 be the
BoundNames ofBindingRestProperty . - Return the
list-concatenation of names1 and names2.
- Return a new empty
List .
- Return the
BoundNames ofBindingRestElement .
- Return the
BoundNames ofBindingElementList .
- Let names1 be the
BoundNames ofBindingElementList . - Let names2 be the
BoundNames ofBindingRestElement . - Return the
list-concatenation of names1 and names2.
- Let names1 be the
BoundNames ofBindingPropertyList . - Let names2 be the
BoundNames ofBindingProperty . - Return the
list-concatenation of names1 and names2.
- Let names1 be the
BoundNames ofBindingElementList . - Let names2 be the
BoundNames ofBindingElisionElement . - Return the
list-concatenation of names1 and names2.
- Return the
BoundNames ofBindingElement .
- Return the
BoundNames ofBindingElement .
- Return the
BoundNames ofBindingIdentifier .
- Return the
BoundNames ofBindingPattern .
- Return the
BoundNames ofForBinding .
- Return the
BoundNames ofBindingIdentifier .
- Return «
"*default*" ».
- Return a new empty
List .
- Let names1 be the
BoundNames ofFormalParameterList . - Let names2 be the
BoundNames ofFunctionRestParameter . - Return the
list-concatenation of names1 and names2.
- Let names1 be the
BoundNames ofFormalParameterList . - Let names2 be the
BoundNames ofFormalParameter . - Return the
list-concatenation of names1 and names2.
- Let formals be the
ArrowFormalParameters that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return the
BoundNames of formals.
- Return the
BoundNames ofBindingIdentifier .
- Return «
"*default*" ».
- Return the
BoundNames ofBindingIdentifier .
- Return «
"*default*" ».
- Return the
BoundNames ofBindingIdentifier .
- Return «
"*default*" ».
- Return the
BoundNames ofBindingIdentifier .
- Return «
"*default*" ».
- Let head be the
AsyncArrowHead that iscovered byCoverCallExpressionAndAsyncArrowHead . - Return the
BoundNames of head.
- Return the
BoundNames ofImportClause .
- Return a new empty
List .
- Let names1 be the
BoundNames ofImportedDefaultBinding . - Let names2 be the
BoundNames ofNameSpaceImport . - Return the
list-concatenation of names1 and names2.
- Let names1 be the
BoundNames ofImportedDefaultBinding . - Let names2 be the
BoundNames ofNamedImports . - Return the
list-concatenation of names1 and names2.
- Return a new empty
List .
- Let names1 be the
BoundNames ofImportsList . - Let names2 be the
BoundNames ofImportSpecifier . - Return the
list-concatenation of names1 and names2.
- Return the
BoundNames ofImportedBinding .
- Return a new empty
List .
- Return the
BoundNames ofVariableStatement .
- Return the
BoundNames ofDeclaration .
- Let declarationNames be the
BoundNames ofHoistableDeclaration . - If declarationNames does not include the element
"*default*" , append"*default*" to declarationNames. - Return declarationNames.
- Let declarationNames be the
BoundNames ofClassDeclaration . - If declarationNames does not include the element
"*default*" , append"*default*" to declarationNames. - Return declarationNames.
- Return «
"*default*" ».
8.2.2 Static Semantics: DeclarationPart
The
- Return
FunctionDeclaration .
- Return
GeneratorDeclaration .
- Return
AsyncFunctionDeclaration .
- Return
AsyncGeneratorDeclaration .
- Return
ClassDeclaration .
- Return
LexicalDeclaration .
8.2.3 Static Semantics: IsConstantDeclaration
The
- Return
IsConstantDeclaration ofLetOrConst .
- Return
false .
- Return
true .
- Return
false .
- Return
false .
- Return
false .
It is not necessary to treat export default
8.2.4 Static Semantics: LexicallyDeclaredNames
The
- Return a new empty
List .
- Let names1 be the
LexicallyDeclaredNames ofStatementList . - Let names2 be the
LexicallyDeclaredNames ofStatementListItem . - Return the
list-concatenation of names1 and names2.
- If
Statement isStatement : LabelledStatement LexicallyDeclaredNames ofLabelledStatement . - Return a new empty
List .
- Return the
BoundNames ofDeclaration .
- Return a new empty
List .
- If the first
CaseClauses is present, let names1 be theLexicallyDeclaredNames of the firstCaseClauses . - Else, let names1 be a new empty
List . - Let names2 be the
LexicallyDeclaredNames ofDefaultClause . - If the second
CaseClauses is present, let names3 be theLexicallyDeclaredNames of the secondCaseClauses . - Else, let names3 be a new empty
List . - Return the
list-concatenation of names1, names2, and names3.
- Let names1 be the
LexicallyDeclaredNames ofCaseClauses . - Let names2 be the
LexicallyDeclaredNames ofCaseClause . - Return the
list-concatenation of names1 and names2.
- If the
StatementList is present, return theLexicallyDeclaredNames ofStatementList . - Return a new empty
List .
- If the
StatementList is present, return theLexicallyDeclaredNames ofStatementList . - Return a new empty
List .
- Return the
LexicallyDeclaredNames ofLabelledItem .
- Return a new empty
List .
- Return the
BoundNames ofFunctionDeclaration .
- Return a new empty
List .
- Return the
TopLevelLexicallyDeclaredNames ofStatementList .
- Return a new empty
List .
- Return the
TopLevelLexicallyDeclaredNames ofStatementList .
- Return a new empty
List .
- Return a new empty
List .
- Return a new empty
List .
- Return the
TopLevelLexicallyDeclaredNames ofStatementList .
At the top level of a
The LexicallyDeclaredNames of a
- Let names1 be the
LexicallyDeclaredNames ofModuleItemList . - Let names2 be the
LexicallyDeclaredNames ofModuleItem . - Return the
list-concatenation of names1 and names2.
- Return the
BoundNames ofImportDeclaration .
- If
ExportDeclaration isexportVariableStatement , return a new emptyList . - Return the
BoundNames ofExportDeclaration .
- Return the
LexicallyDeclaredNames ofStatementListItem .
At the top level of a
8.2.5 Static Semantics: LexicallyScopedDeclarations
The
- Let declarations1 be the
LexicallyScopedDeclarations ofStatementList . - Let declarations2 be the
LexicallyScopedDeclarations ofStatementListItem . - Return the
list-concatenation of declarations1 and declarations2.
- If
Statement isStatement : LabelledStatement LexicallyScopedDeclarations ofLabelledStatement . - Return a new empty
List .
- Return a
List whose sole element is theDeclarationPart ofDeclaration .
- Return a new empty
List .
- If the first
CaseClauses is present, let declarations1 be theLexicallyScopedDeclarations of the firstCaseClauses . - Else, let declarations1 be a new empty
List . - Let declarations2 be the
LexicallyScopedDeclarations ofDefaultClause . - If the second
CaseClauses is present, let declarations3 be theLexicallyScopedDeclarations of the secondCaseClauses . - Else, let declarations3 be a new empty
List . - Return the
list-concatenation of declarations1, declarations2, and declarations3.
- Let declarations1 be the
LexicallyScopedDeclarations ofCaseClauses . - Let declarations2 be the
LexicallyScopedDeclarations ofCaseClause . - Return the
list-concatenation of declarations1 and declarations2.
- If the
StatementList is present, return theLexicallyScopedDeclarations ofStatementList . - Return a new empty
List .
- If the
StatementList is present, return theLexicallyScopedDeclarations ofStatementList . - Return a new empty
List .
- Return the
LexicallyScopedDeclarations ofLabelledItem .
- Return a new empty
List .
- Return «
FunctionDeclaration ».
- Return a new empty
List .
- Return the
TopLevelLexicallyScopedDeclarations ofStatementList .
- Return a new empty
List .
- Return the
TopLevelLexicallyScopedDeclarations ofStatementList .
- Return a new empty
List .
- Return a new empty
List .
- Return a new empty
List .
- Return the
TopLevelLexicallyScopedDeclarations ofStatementList .
- Return a new empty
List .
- Let declarations1 be the
LexicallyScopedDeclarations ofModuleItemList . - Let declarations2 be the
LexicallyScopedDeclarations ofModuleItem . - Return the
list-concatenation of declarations1 and declarations2.
- Return a new empty
List .
- Return a new empty
List .
- Return a
List whose sole element is theDeclarationPart ofDeclaration .
- Return a
List whose sole element is theDeclarationPart ofHoistableDeclaration .
- Return a
List whose sole element isClassDeclaration .
- Return a
List whose sole element is thisExportDeclaration .
8.2.6 Static Semantics: VarDeclaredNames
The
- Return a new empty
List .
- Return a new empty
List .
- Let names1 be the
VarDeclaredNames ofStatementList . - Let names2 be the
VarDeclaredNames ofStatementListItem . - Return the
list-concatenation of names1 and names2.
- Return a new empty
List .
- Return the
BoundNames ofVariableDeclarationList .
- Let names1 be the
VarDeclaredNames of the firstStatement . - Let names2 be the
VarDeclaredNames of the secondStatement . - Return the
list-concatenation of names1 and names2.
- Return the
VarDeclaredNames ofStatement .
- Return the
VarDeclaredNames ofStatement .
- Return the
VarDeclaredNames ofStatement .
- Return the
VarDeclaredNames ofStatement .
- Let names1 be the
BoundNames ofVariableDeclarationList . - Let names2 be the
VarDeclaredNames ofStatement . - Return the
list-concatenation of names1 and names2.
- Return the
VarDeclaredNames ofStatement .
- Return the
VarDeclaredNames ofStatement .
- Let names1 be the
BoundNames ofForBinding . - Let names2 be the
VarDeclaredNames ofStatement . - Return the
list-concatenation of names1 and names2.
This section is extended by Annex
- Return the
VarDeclaredNames ofStatement .
- Return the
VarDeclaredNames ofCaseBlock .
- Return a new empty
List .
- If the first
CaseClauses is present, let names1 be theVarDeclaredNames of the firstCaseClauses . - Else, let names1 be a new empty
List . - Let names2 be the
VarDeclaredNames ofDefaultClause . - If the second
CaseClauses is present, let names3 be theVarDeclaredNames of the secondCaseClauses . - Else, let names3 be a new empty
List . - Return the
list-concatenation of names1, names2, and names3.
- Let names1 be the
VarDeclaredNames ofCaseClauses . - Let names2 be the
VarDeclaredNames ofCaseClause . - Return the
list-concatenation of names1 and names2.
- If the
StatementList is present, return theVarDeclaredNames ofStatementList . - Return a new empty
List .
- If the
StatementList is present, return theVarDeclaredNames ofStatementList . - Return a new empty
List .
- Return the
VarDeclaredNames ofLabelledItem .
- Return a new empty
List .
- Let names1 be the
VarDeclaredNames ofBlock . - Let names2 be the
VarDeclaredNames ofCatch . - Return the
list-concatenation of names1 and names2.
- Let names1 be the
VarDeclaredNames ofBlock . - Let names2 be the
VarDeclaredNames ofFinally . - Return the
list-concatenation of names1 and names2.
- Let names1 be the
VarDeclaredNames ofBlock . - Let names2 be the
VarDeclaredNames ofCatch . - Let names3 be the
VarDeclaredNames ofFinally . - Return the
list-concatenation of names1, names2, and names3.
- Return the
VarDeclaredNames ofBlock .
- Return a new empty
List .
- Return the
TopLevelVarDeclaredNames ofStatementList .
- Return a new empty
List .
- Return the
TopLevelVarDeclaredNames ofStatementList .
- Return a new empty
List .
- Return a new empty
List .
- Return a new empty
List .
- Return the
TopLevelVarDeclaredNames ofStatementList .
- Let names1 be the
VarDeclaredNames ofModuleItemList . - Let names2 be the
VarDeclaredNames ofModuleItem . - Return the
list-concatenation of names1 and names2.
- Return a new empty
List .
- If
ExportDeclaration isexportVariableStatement , return theBoundNames ofExportDeclaration . - Return a new empty
List .
8.2.7 Static Semantics: VarScopedDeclarations
The
- Return a new empty
List .
- Return a new empty
List .
- Let declarations1 be the
VarScopedDeclarations ofStatementList . - Let declarations2 be the
VarScopedDeclarations ofStatementListItem . - Return the
list-concatenation of declarations1 and declarations2.
- Return a new empty
List .
- Return «
VariableDeclaration ».
- Let declarations1 be the
VarScopedDeclarations ofVariableDeclarationList . - Return the
list-concatenation of declarations1 and «VariableDeclaration ».
- Let declarations1 be the
VarScopedDeclarations of the firstStatement . - Let declarations2 be the
VarScopedDeclarations of the secondStatement . - Return the
list-concatenation of declarations1 and declarations2.
- Return the
VarScopedDeclarations ofStatement .
- Return the
VarScopedDeclarations ofStatement .
- Return the
VarScopedDeclarations ofStatement .
- Return the
VarScopedDeclarations ofStatement .
- Let declarations1 be the
VarScopedDeclarations ofVariableDeclarationList . - Let declarations2 be the
VarScopedDeclarations ofStatement . - Return the
list-concatenation of declarations1 and declarations2.
- Return the
VarScopedDeclarations ofStatement .
- Return the
VarScopedDeclarations ofStatement .
- Let declarations1 be «
ForBinding ». - Let declarations2 be the
VarScopedDeclarations ofStatement . - Return the
list-concatenation of declarations1 and declarations2.
This section is extended by Annex
- Return the
VarScopedDeclarations ofStatement .
- Return the
VarScopedDeclarations ofCaseBlock .
- Return a new empty
List .
- If the first
CaseClauses is present, let declarations1 be theVarScopedDeclarations of the firstCaseClauses . - Else, let declarations1 be a new empty
List . - Let declarations2 be the
VarScopedDeclarations ofDefaultClause . - If the second
CaseClauses is present, let declarations3 be theVarScopedDeclarations of the secondCaseClauses . - Else, let declarations3 be a new empty
List . - Return the
list-concatenation of declarations1, declarations2, and declarations3.
- Let declarations1 be the
VarScopedDeclarations ofCaseClauses . - Let declarations2 be the
VarScopedDeclarations ofCaseClause . - Return the
list-concatenation of declarations1 and declarations2.
- If the
StatementList is present, return theVarScopedDeclarations ofStatementList . - Return a new empty
List .
- If the
StatementList is present, return theVarScopedDeclarations ofStatementList . - Return a new empty
List .
- Return the
VarScopedDeclarations ofLabelledItem .
- Return a new empty
List .
- Let declarations1 be the
VarScopedDeclarations ofBlock . - Let declarations2 be the
VarScopedDeclarations ofCatch . - Return the
list-concatenation of declarations1 and declarations2.
- Let declarations1 be the
VarScopedDeclarations ofBlock . - Let declarations2 be the
VarScopedDeclarations ofFinally . - Return the
list-concatenation of declarations1 and declarations2.
- Let declarations1 be the
VarScopedDeclarations ofBlock . - Let declarations2 be the
VarScopedDeclarations ofCatch . - Let declarations3 be the
VarScopedDeclarations ofFinally . - Return the
list-concatenation of declarations1, declarations2, and declarations3.
- Return the
VarScopedDeclarations ofBlock .
- Return a new empty
List .
- Return the
TopLevelVarScopedDeclarations ofStatementList .
- Return a new empty
List .
- Return the
TopLevelVarScopedDeclarations ofStatementList .
- Return a new empty
List .
- Return a new empty
List .
- Return a new empty
List .
- Return the
TopLevelVarScopedDeclarations ofStatementList .
- Return a new empty
List .
- Let declarations1 be the
VarScopedDeclarations ofModuleItemList . - Let declarations2 be the
VarScopedDeclarations ofModuleItem . - Return the
list-concatenation of declarations1 and declarations2.
- Return a new empty
List .
- If
ExportDeclaration isexportVariableStatement , return theVarScopedDeclarations ofVariableStatement . - Return a new empty
List .
8.2.8 Static Semantics: TopLevelLexicallyDeclaredNames
The
- Let names1 be the
TopLevelLexicallyDeclaredNames ofStatementList . - Let names2 be the
TopLevelLexicallyDeclaredNames ofStatementListItem . - Return the
list-concatenation of names1 and names2.
- Return a new empty
List .
- If
Declaration isDeclaration : HoistableDeclaration - Return a new empty
List .
- Return a new empty
- Return the
BoundNames ofDeclaration .
At the top level of a function, or script, function declarations are treated like var declarations rather than like lexical declarations.
8.2.9 Static Semantics: TopLevelLexicallyScopedDeclarations
The
- Let declarations1 be the
TopLevelLexicallyScopedDeclarations ofStatementList . - Let declarations2 be the
TopLevelLexicallyScopedDeclarations ofStatementListItem . - Return the
list-concatenation of declarations1 and declarations2.
- Return a new empty
List .
- If
Declaration isDeclaration : HoistableDeclaration - Return a new empty
List .
- Return a new empty
- Return «
Declaration ».
8.2.10 Static Semantics: TopLevelVarDeclaredNames
The
- Let names1 be the
TopLevelVarDeclaredNames ofStatementList . - Let names2 be the
TopLevelVarDeclaredNames ofStatementListItem . - Return the
list-concatenation of names1 and names2.
- If
Declaration isDeclaration : HoistableDeclaration - Return the
BoundNames ofHoistableDeclaration .
- Return the
- Return a new empty
List .
- If
Statement isStatement : LabelledStatement TopLevelVarDeclaredNames ofStatement . - Return the
VarDeclaredNames ofStatement .
At the top level of a function or script, inner function declarations are treated like var declarations.
- Return the
TopLevelVarDeclaredNames ofLabelledItem .
- If
Statement isStatement : LabelledStatement TopLevelVarDeclaredNames ofStatement . - Return the
VarDeclaredNames ofStatement .
- Return the
BoundNames ofFunctionDeclaration .
8.2.11 Static Semantics: TopLevelVarScopedDeclarations
The
- Let declarations1 be the
TopLevelVarScopedDeclarations ofStatementList . - Let declarations2 be the
TopLevelVarScopedDeclarations ofStatementListItem . - Return the
list-concatenation of declarations1 and declarations2.
- If
Statement isStatement : LabelledStatement TopLevelVarScopedDeclarations ofStatement . - Return the
VarScopedDeclarations ofStatement .
- If
Declaration isDeclaration : HoistableDeclaration - Let declaration be the
DeclarationPart ofHoistableDeclaration . - Return « declaration ».
- Let declaration be the
- Return a new empty
List .
- Return the
TopLevelVarScopedDeclarations ofLabelledItem .
- If
Statement isStatement : LabelledStatement TopLevelVarScopedDeclarations ofStatement . - Return the
VarScopedDeclarations ofStatement .
- Return «
FunctionDeclaration ».
8.3 Labels
8.3.1 Static Semantics: ContainsDuplicateLabels
The
- Return
false .
- Let hasDuplicates be
ContainsDuplicateLabels ofStatementList with argument labelSet. - If hasDuplicates is
true , returntrue . - Return
ContainsDuplicateLabels ofStatementListItem with argument labelSet.
- Let hasDuplicate be
ContainsDuplicateLabels of the firstStatement with argument labelSet. - If hasDuplicate is
true , returntrue . - Return
ContainsDuplicateLabels of the secondStatement with argument labelSet.
- Return
ContainsDuplicateLabels ofStatement with argument labelSet.
- Return
ContainsDuplicateLabels ofStatement with argument labelSet.
- Return
ContainsDuplicateLabels ofStatement with argument labelSet.
- Return
ContainsDuplicateLabels ofStatement with argument labelSet.
- Return
ContainsDuplicateLabels ofStatement with argument labelSet.
This section is extended by Annex
- Return
ContainsDuplicateLabels ofStatement with argument labelSet.
- Return
ContainsDuplicateLabels ofCaseBlock with argument labelSet.
- Return
false .
- If the first
CaseClauses is present, then- If
ContainsDuplicateLabels of the firstCaseClauses with argument labelSet istrue , returntrue .
- If
- If
ContainsDuplicateLabels ofDefaultClause with argument labelSet istrue , returntrue . - If the second
CaseClauses is not present, returnfalse . - Return
ContainsDuplicateLabels of the secondCaseClauses with argument labelSet.
- Let hasDuplicates be
ContainsDuplicateLabels ofCaseClauses with argument labelSet. - If hasDuplicates is
true , returntrue . - Return
ContainsDuplicateLabels ofCaseClause with argument labelSet.
- If the
StatementList is present, returnContainsDuplicateLabels ofStatementList with argument labelSet. - Return
false .
- If the
StatementList is present, returnContainsDuplicateLabels ofStatementList with argument labelSet. - Return
false .
- Let label be the
StringValue ofLabelIdentifier . - If labelSet contains label, return
true . - Let newLabelSet be the
list-concatenation of labelSet and « label ». - Return
ContainsDuplicateLabels ofLabelledItem with argument newLabelSet.
- Return
false .
- Let hasDuplicates be
ContainsDuplicateLabels ofBlock with argument labelSet. - If hasDuplicates is
true , returntrue . - Return
ContainsDuplicateLabels ofCatch with argument labelSet.
- Let hasDuplicates be
ContainsDuplicateLabels ofBlock with argument labelSet. - If hasDuplicates is
true , returntrue . - Return
ContainsDuplicateLabels ofFinally with argument labelSet.
- If
ContainsDuplicateLabels ofBlock with argument labelSet istrue , returntrue . - If
ContainsDuplicateLabels ofCatch with argument labelSet istrue , returntrue . - Return
ContainsDuplicateLabels ofFinally with argument labelSet.
- Return
ContainsDuplicateLabels ofBlock with argument labelSet.
- Return
false .
- Return
false .
- Let hasDuplicates be
ContainsDuplicateLabels ofModuleItemList with argument labelSet. - If hasDuplicates is
true , returntrue . - Return
ContainsDuplicateLabels ofModuleItem with argument labelSet.
- Return
false .
8.3.2 Static Semantics: ContainsUndefinedBreakTarget
The
- Return
false .
- Let hasUndefinedLabels be
ContainsUndefinedBreakTarget ofStatementList with argument labelSet. - If hasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedBreakTarget ofStatementListItem with argument labelSet.
- Let hasUndefinedLabels be
ContainsUndefinedBreakTarget of the firstStatement with argument labelSet. - If hasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedBreakTarget of the secondStatement with argument labelSet.
- Return
ContainsUndefinedBreakTarget ofStatement with argument labelSet.
- Return
ContainsUndefinedBreakTarget ofStatement with argument labelSet.
- Return
ContainsUndefinedBreakTarget ofStatement with argument labelSet.
- Return
ContainsUndefinedBreakTarget ofStatement with argument labelSet.
- Return
ContainsUndefinedBreakTarget ofStatement with argument labelSet.
This section is extended by Annex
- Return
false .
- If labelSet does not contain the
StringValue ofLabelIdentifier , returntrue . - Return
false .
- Return
ContainsUndefinedBreakTarget ofStatement with argument labelSet.
- Return
ContainsUndefinedBreakTarget ofCaseBlock with argument labelSet.
- Return
false .
- If the first
CaseClauses is present, then- If
ContainsUndefinedBreakTarget of the firstCaseClauses with argument labelSet istrue , returntrue .
- If
- If
ContainsUndefinedBreakTarget ofDefaultClause with argument labelSet istrue , returntrue . - If the second
CaseClauses is not present, returnfalse . - Return
ContainsUndefinedBreakTarget of the secondCaseClauses with argument labelSet.
- Let hasUndefinedLabels be
ContainsUndefinedBreakTarget ofCaseClauses with argument labelSet. - If hasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedBreakTarget ofCaseClause with argument labelSet.
- If the
StatementList is present, returnContainsUndefinedBreakTarget ofStatementList with argument labelSet. - Return
false .
- If the
StatementList is present, returnContainsUndefinedBreakTarget ofStatementList with argument labelSet. - Return
false .
- Let label be the
StringValue ofLabelIdentifier . - Let newLabelSet be the
list-concatenation of labelSet and « label ». - Return
ContainsUndefinedBreakTarget ofLabelledItem with argument newLabelSet.
- Return
false .
- Let hasUndefinedLabels be
ContainsUndefinedBreakTarget ofBlock with argument labelSet. - If hasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedBreakTarget ofCatch with argument labelSet.
- Let hasUndefinedLabels be
ContainsUndefinedBreakTarget ofBlock with argument labelSet. - If hasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedBreakTarget ofFinally with argument labelSet.
- If
ContainsUndefinedBreakTarget ofBlock with argument labelSet istrue , returntrue . - If
ContainsUndefinedBreakTarget ofCatch with argument labelSet istrue , returntrue . - Return
ContainsUndefinedBreakTarget ofFinally with argument labelSet.
- Return
ContainsUndefinedBreakTarget ofBlock with argument labelSet.
- Return
false .
- Return
false .
- Let hasUndefinedLabels be
ContainsUndefinedBreakTarget ofModuleItemList with argument labelSet. - If hasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedBreakTarget ofModuleItem with argument labelSet.
- Return
false .
8.3.3 Static Semantics: ContainsUndefinedContinueTarget
The
- Return
false .
- Return
ContainsUndefinedContinueTarget ofBlockStatement with arguments iterationSet and « ».
- Let newIterationSet be the
list-concatenation of iterationSet and labelSet. - Return
ContainsUndefinedContinueTarget ofIterationStatement with arguments newIterationSet and « ».
- Let hasUndefinedLabels be
ContainsUndefinedContinueTarget ofStatementList with arguments iterationSet and « ». - If hasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedContinueTarget ofStatementListItem with arguments iterationSet and « ».
- Let hasUndefinedLabels be
ContainsUndefinedContinueTarget of the firstStatement with arguments iterationSet and « ». - If hasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedContinueTarget of the secondStatement with arguments iterationSet and « ».
- Return
ContainsUndefinedContinueTarget ofStatement with arguments iterationSet and « ».
- Return
ContainsUndefinedContinueTarget ofStatement with arguments iterationSet and « ».
- Return
ContainsUndefinedContinueTarget ofStatement with arguments iterationSet and « ».
- Return
ContainsUndefinedContinueTarget ofStatement with arguments iterationSet and « ».
- Return
ContainsUndefinedContinueTarget ofStatement with arguments iterationSet and « ».
This section is extended by Annex
- Return
false .
- If iterationSet does not contain the
StringValue ofLabelIdentifier , returntrue . - Return
false .
- Return
ContainsUndefinedContinueTarget ofStatement with arguments iterationSet and « ».
- Return
ContainsUndefinedContinueTarget ofCaseBlock with arguments iterationSet and « ».
- Return
false .
- If the first
CaseClauses is present, then- If
ContainsUndefinedContinueTarget of the firstCaseClauses with arguments iterationSet and « » istrue , returntrue .
- If
- If
ContainsUndefinedContinueTarget ofDefaultClause with arguments iterationSet and « » istrue , returntrue . - If the second
CaseClauses is not present, returnfalse . - Return
ContainsUndefinedContinueTarget of the secondCaseClauses with arguments iterationSet and « ».
- Let hasUndefinedLabels be
ContainsUndefinedContinueTarget ofCaseClauses with arguments iterationSet and « ». - If hasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedContinueTarget ofCaseClause with arguments iterationSet and « ».
- If the
StatementList is present, returnContainsUndefinedContinueTarget ofStatementList with arguments iterationSet and « ». - Return
false .
- If the
StatementList is present, returnContainsUndefinedContinueTarget ofStatementList with arguments iterationSet and « ». - Return
false .
- Let label be the
StringValue ofLabelIdentifier . - Let newLabelSet be the
list-concatenation of labelSet and « label ». - Return
ContainsUndefinedContinueTarget ofLabelledItem with arguments iterationSet and newLabelSet.
- Return
false .
- Let hasUndefinedLabels be
ContainsUndefinedContinueTarget ofBlock with arguments iterationSet and « ». - If hasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedContinueTarget ofCatch with arguments iterationSet and « ».
- Let hasUndefinedLabels be
ContainsUndefinedContinueTarget ofBlock with arguments iterationSet and « ». - If hasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedContinueTarget ofFinally with arguments iterationSet and « ».
- If
ContainsUndefinedContinueTarget ofBlock with arguments iterationSet and « » istrue , returntrue . - If
ContainsUndefinedContinueTarget ofCatch with arguments iterationSet and « » istrue , returntrue . - Return
ContainsUndefinedContinueTarget ofFinally with arguments iterationSet and « ».
- Return
ContainsUndefinedContinueTarget ofBlock with arguments iterationSet and « ».
- Return
false .
- Return
false .
- Let hasUndefinedLabels be
ContainsUndefinedContinueTarget ofModuleItemList with arguments iterationSet and « ». - If hasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedContinueTarget ofModuleItem with arguments iterationSet and « ».
- Return
false .
8.4 Function Name Inference
8.4.1 Static Semantics: HasName
The
- Let expr be the
ParenthesizedExpression that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - If
IsFunctionDefinition of expr isfalse , returnfalse . - Return
HasName of expr.
- Return
false .
- Return
true .
8.4.2 Static Semantics: IsFunctionDefinition
The
- Let expr be the
ParenthesizedExpression that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return
IsFunctionDefinition of expr.
- Return
false .
- Return
true .
8.4.3 Static Semantics: IsAnonymousFunctionDefinition ( expr )
The abstract operation IsAnonymousFunctionDefinition takes argument expr (an
- If
IsFunctionDefinition of expr isfalse , returnfalse . - Let hasName be
HasName of expr. - If hasName is
true , returnfalse . - Return
true .
8.4.4 Static Semantics: IsIdentifierRef
The
- Return
true .
- Return
false .
8.4.5 Runtime Semantics: NamedEvaluation
The
- Let expr be the
ParenthesizedExpression that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return ?
NamedEvaluation of expr with argument name.
Assert :IsAnonymousFunctionDefinition (Expression ) istrue .- Return ?
NamedEvaluation ofExpression with argument name.
- Return
InstantiateOrdinaryFunctionExpression ofFunctionExpression with argument name.
- Return
InstantiateGeneratorFunctionExpression ofGeneratorExpression with argument name.
- Return
InstantiateAsyncGeneratorFunctionExpression ofAsyncGeneratorExpression with argument name.
- Return
InstantiateAsyncFunctionExpression ofAsyncFunctionExpression with argument name.
- Return
InstantiateArrowFunctionExpression ofArrowFunction with argument name.
- Return
InstantiateAsyncArrowFunctionExpression ofAsyncArrowFunction with argument name.
- Let value be ?
ClassDefinitionEvaluation ofClassTail with argumentsundefined and name. - Set value.[[SourceText]] to the
source text matched by ClassExpression . - Return value.
8.5 Contains
8.5.1 Static Semantics: Contains
The
Every grammar production alternative in this specification which is not listed below implicitly has the following default definition of Contains:
- For each child node child of this
Parse Node , do- If child is an instance of symbol, return
true . - If child is an instance of a nonterminal, then
- Let contained be the result of child
Contains symbol. - If contained is
true , returntrue .
- Let contained be the result of child
- If child is an instance of symbol, return
- Return
false .
- Return
false .
Static semantic rules that depend upon substructure generally do not look into function definitions.
- If symbol is
ClassBody , returntrue . - If symbol is
ClassHeritage , then- If
ClassHeritage is present, returntrue ; otherwise returnfalse .
- If
- If
ClassHeritage is present, then- If
ClassHeritage Contains symbol istrue , returntrue .
- If
- Return the result of
ComputedPropertyContains ofClassBody with argument symbol.
Static semantic rules that depend upon substructure generally do not look into class bodies except for
- Return
false .
Static semantic rules that depend upon substructure generally do not look into static initialization blocks.
- If symbol is not one of
NewTarget ,SuperProperty ,SuperCall ,super, orthis, returnfalse . - If
ArrowParameters Contains symbol istrue , returntrue . - Return
ConciseBody Contains symbol.
- Let formals be the
ArrowFormalParameters that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return formals
Contains symbol.
- If symbol is not one of
NewTarget ,SuperProperty ,SuperCall ,super, orthis, returnfalse . - Return
AsyncConciseBody Contains symbol.
- If symbol is not one of
NewTarget ,SuperProperty ,SuperCall ,super, orthis, returnfalse . - Let head be the
AsyncArrowHead that iscovered byCoverCallExpressionAndAsyncArrowHead . - If head
Contains symbol istrue , returntrue . - Return
AsyncConciseBody Contains symbol.
Contains is used to detect new.target, this, and super usage within an
- If symbol is
MethodDefinition , returntrue . - Return the result of
ComputedPropertyContains ofMethodDefinition with argument symbol.
- Return
false .
- If
MemberExpression Contains symbol istrue , returntrue . - Return
false .
- If symbol is the
ReservedWord super, returntrue . - Return
false .
- If
CallExpression Contains symbol istrue , returntrue . - Return
false .
- Return
false .
- If
OptionalChain Contains symbol istrue , returntrue . - Return
false .
8.5.2 Static Semantics: ComputedPropertyContains
The
- Return
false .
- Return the result of
ComputedPropertyName Contains symbol.
- Return the result of
ComputedPropertyContains ofClassElementName with argument symbol.
- Return the result of
ComputedPropertyContains ofClassElementName with argument symbol.
- Return the result of
ComputedPropertyContains ofClassElementName with argument symbol.
- Let inList be
ComputedPropertyContains ofClassElementList with argument symbol. - If inList is
true , returntrue . - Return the result of
ComputedPropertyContains ofClassElement with argument symbol.
- Return
false .
- Return
false .
- Return the result of
ComputedPropertyContains ofClassElementName with argument symbol.
- Return the result of
ComputedPropertyContains ofClassElementName with argument symbol.
8.6 Miscellaneous
These operations are used in multiple places throughout the specification.
8.6.1 Runtime Semantics: InstantiateFunctionObject
The
- Return
InstantiateOrdinaryFunctionObject ofFunctionDeclaration with arguments env and privateEnv.
- Return
InstantiateGeneratorFunctionObject ofGeneratorDeclaration with arguments env and privateEnv.
- Return
InstantiateAsyncGeneratorFunctionObject ofAsyncGeneratorDeclaration with arguments env and privateEnv.
- Return
InstantiateAsyncFunctionObject ofAsyncFunctionDeclaration with arguments env and privateEnv.
8.6.2 Runtime Semantics: BindingInitialization
The
var statements and formal parameter lists of some
It is defined piecewise over the following productions:
- Let name be the
StringValue ofIdentifier . - Return ?
InitializeBoundName (name, value, environment).
- Return ?
InitializeBoundName ("yield" , value, environment).
- Return ?
InitializeBoundName ("await" , value, environment).
- Perform ?
RequireObjectCoercible (value). - Return ?
BindingInitialization ofObjectBindingPattern with arguments value and environment.
- Let iteratorRecord be ?
GetIterator (value,sync ). - Let result be
Completion (IteratorBindingInitialization ofArrayBindingPattern with arguments iteratorRecord and environment). - If iteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord, result). - Return ? result.
- Return
unused .
- Perform ?
PropertyBindingInitialization ofBindingPropertyList with arguments value and environment. - Return
unused .
- Let excludedNames be a new empty
List . - Return ?
RestBindingInitialization ofBindingRestProperty with arguments value, environment, and excludedNames.
- Let excludedNames be ?
PropertyBindingInitialization ofBindingPropertyList with arguments value and environment. - Return ?
RestBindingInitialization ofBindingRestProperty with arguments value, environment, and excludedNames.
8.6.2.1 InitializeBoundName ( name, value, environment )
The abstract operation InitializeBoundName takes arguments name (a String), value (an
- If environment is not
undefined , then- Perform ! environment.InitializeBinding(name, value).
- Return
unused .
- Else,
- Let lhs be ?
ResolveBinding (name). - Return ?
PutValue (lhs, value).
- Let lhs be ?
8.6.3 Runtime Semantics: IteratorBindingInitialization
The
When
It is defined piecewise over the following productions:
- Return
unused .
- Return ?
IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord.
- If
Elision is present, then- Perform ?
IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord.
- Perform ?
- Return ?
IteratorBindingInitialization ofBindingRestElement with arguments iteratorRecord and environment.
- Perform ?
IteratorBindingInitialization ofBindingElementList with arguments iteratorRecord and environment. - Return ?
IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord.
- Perform ?
IteratorBindingInitialization ofBindingElementList with arguments iteratorRecord and environment. - If
Elision is present, then- Perform ?
IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord.
- Perform ?
- Return ?
IteratorBindingInitialization ofBindingRestElement with arguments iteratorRecord and environment.
- Perform ?
IteratorBindingInitialization ofBindingElementList with arguments iteratorRecord and environment. - Return ?
IteratorBindingInitialization ofBindingElisionElement with arguments iteratorRecord and environment.
- Perform ?
IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord. - Return ?
IteratorBindingInitialization ofBindingElement with arguments iteratorRecord and environment.
- Let bindingId be the
StringValue ofBindingIdentifier . - Let lhs be ?
ResolveBinding (bindingId, environment). - Let v be
undefined . - If iteratorRecord.[[Done]] is
false , then- Let next be ?
IteratorStepValue (iteratorRecord). - If next is not
done , then- Set v to next.
- Let next be ?
- If
Initializer is present and v isundefined , then- If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Set v to ?
NamedEvaluation ofInitializer with argument bindingId.
- Set v to ?
- Else,
- Let defaultValue be ?
Evaluation ofInitializer . - Set v to ?
GetValue (defaultValue).
- Let defaultValue be ?
- If
- If environment is
undefined , return ?PutValue (lhs, v). - Return ?
InitializeReferencedBinding (lhs, v).
- Let v be
undefined . - If iteratorRecord.[[Done]] is
false , then- Let next be ?
IteratorStepValue (iteratorRecord). - If next is not
done , then- Set v to next.
- Let next be ?
- If
Initializer is present and v isundefined , then- Let defaultValue be ?
Evaluation ofInitializer . - Set v to ?
GetValue (defaultValue).
- Let defaultValue be ?
- Return ?
BindingInitialization ofBindingPattern with arguments v and environment.
- Let lhs be ?
ResolveBinding (StringValue ofBindingIdentifier , environment). - Let A be !
ArrayCreate (0). - Let n be 0.
- Repeat,
- Let next be
done . - If iteratorRecord.[[Done]] is
false , then- Set next to ?
IteratorStepValue (iteratorRecord).
- Set next to ?
- If next is
done , then- If environment is
undefined , return ?PutValue (lhs, A). - Return ?
InitializeReferencedBinding (lhs, A).
- If environment is
- Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)), next). - Set n to n + 1.
- Let next be
- Let A be !
ArrayCreate (0). - Let n be 0.
- Repeat,
- Let next be
done . - If iteratorRecord.[[Done]] is
false , then- Set next to ?
IteratorStepValue (iteratorRecord).
- Set next to ?
- If next is
done , then- Return ?
BindingInitialization ofBindingPattern with arguments A and environment.
- Return ?
- Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)), next). - Set n to n + 1.
- Let next be
- Return
unused .
- Perform ?
IteratorBindingInitialization ofFormalParameterList with arguments iteratorRecord and environment. - Return ?
IteratorBindingInitialization ofFunctionRestParameter with arguments iteratorRecord and environment.
- Perform ?
IteratorBindingInitialization ofFormalParameterList with arguments iteratorRecord and environment. - Return ?
IteratorBindingInitialization ofFormalParameter with arguments iteratorRecord and environment.
- Let v be
undefined . Assert : iteratorRecord.[[Done]] isfalse .- Let next be ?
IteratorStepValue (iteratorRecord). - If next is not
done , then- Set v to next.
- Return ?
BindingInitialization ofBindingIdentifier with arguments v and environment.
- Let formals be the
ArrowFormalParameters that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return ?
IteratorBindingInitialization of formals with arguments iteratorRecord and environment.
- Let v be
undefined . Assert : iteratorRecord.[[Done]] isfalse .- Let next be ?
IteratorStepValue (iteratorRecord). - If next is not
done , then- Set v to next.
- Return ?
BindingInitialization ofBindingIdentifier with arguments v and environment.
8.6.4 Static Semantics: AssignmentTargetType
The
- If
IsStrict (thisIdentifierReference ) istrue and theStringValue ofIdentifier is either"eval" or"arguments" , returninvalid . - Return
simple .
- Return
simple .
- Let expr be the
ParenthesizedExpression that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return the
AssignmentTargetType of expr.
- Return
invalid .
8.6.5 Static Semantics: PropName
The
- Return the
StringValue ofIdentifierReference .
- Return
empty .
- Return the
PropName ofPropertyName .
- Return the
StringValue ofIdentifierName .
- Return the
SV ofStringLiteral .
- Let nbr be the
NumericValue ofNumericLiteral . - Return !
ToString (nbr).
- Return
empty .
- Return the
PropName ofClassElementName .
- Return the
PropName ofClassElementName .
- Return the
PropName ofClassElementName .
- Return
empty .
- Return
empty .
- Return the
PropName ofClassElementName .
- Return the
PropName ofClassElementName .
- Return
empty .
9 Executable Code and Execution Contexts
9.1 Environment Records
Environment Record is a specification type used to define the association of
Every Environment Record has an [[OuterEnv]] field, which is either
Environment Records are purely specification mechanisms and need not correspond to any specific artefact of an ECMAScript implementation. It is impossible for an ECMAScript program to directly access or manipulate such values.
9.1.1 The Environment Record Type Hierarchy
-
Environment Record (abstract)-
A
Declarative Environment Record is used to define the effect of ECMAScript language syntactic elements such asFunctionDeclaration s,VariableDeclaration s, andCatch clauses that directly associate identifier bindings withECMAScript language values .-
A
Function Environment Record corresponds to the invocation of an ECMAScriptfunction object , and contains bindings for the top-level declarations within that function. It may establish a newthisbinding. It also captures the state necessary to supportsupermethod invocations. -
A
Module Environment Record contains the bindings for the top-level declarations of aModule . It also contains the bindings that are explicitly imported by theModule . Its [[OuterEnv]] is aGlobal Environment Record .
-
-
An
Object Environment Record is used to define the effect of ECMAScript elements such asWithStatement that associate identifier bindings with the properties of some object. -
A
Global Environment Record is used forScript global declarations. It does not have an outer environment; its [[OuterEnv]] isnull . It may be prepopulated with identifier bindings and it includes an associatedglobal object whose properties provide some of the global environment's identifier bindings. As ECMAScript code is executed, additional properties may be added to theglobal object and the initial properties may be modified.
-
The
| Method | Purpose |
|---|---|
| HasBinding(N) |
Determine if an |
| CreateMutableBinding(N, D) |
Create a new but uninitialized mutable binding in an |
| CreateImmutableBinding(N, S) |
Create a new but uninitialized immutable binding in an |
| InitializeBinding(N, V) |
Set the value of an already existing but uninitialized binding in an |
| SetMutableBinding(N, V, S) |
Set the value of an already existing mutable binding in an |
| GetBindingValue(N, S) |
Returns the value of an already existing binding from an |
| DeleteBinding(N) |
Delete a binding from an |
| HasThisBinding() |
Determine if an this binding. Return |
| HasSuperBinding() |
Determine if an super method binding. Return |
| WithBaseObject() |
If this with statement, return the with object. Otherwise, return |
9.1.1.1 Declarative Environment Records
Each Declarative Environment Record is associated with an ECMAScript program scope containing variable, constant, let, class, module, import, and/or function declarations. A Declarative Environment Record binds the set of identifiers defined by the declarations contained within its scope.
9.1.1.1.1 HasBinding ( N )
The HasBinding concrete method of a
- If envRec has a binding for N, return
true . - Return
false .
9.1.1.1.2 CreateMutableBinding ( N, D )
The CreateMutableBinding concrete method of a
Assert : envRec does not already have a binding for N.- Create a mutable binding in envRec for N and record that it is uninitialized. If D is
true , record that the newly created binding may be deleted by a subsequent DeleteBinding call. - Return
unused .
9.1.1.1.3 CreateImmutableBinding ( N, S )
The CreateImmutableBinding concrete method of a
Assert : envRec does not already have a binding for N.- Create an immutable binding in envRec for N and record that it is uninitialized. If S is
true , record that the newly created binding is a strict binding. - Return
unused .
9.1.1.1.4 InitializeBinding ( N, V )
The InitializeBinding concrete method of a
Assert : envRec must have an uninitialized binding for N.- Set the bound value for N in envRec to V.
Record that the binding for N in envRec has been initialized.- Return
unused .
9.1.1.1.5 SetMutableBinding ( N, V, S )
The SetMutableBinding concrete method of a
- If envRec does not have a binding for N, then
- If S is
true , throw aReferenceError exception. - Perform ! envRec.CreateMutableBinding(N,
true ). - Perform ! envRec.InitializeBinding(N, V).
- Return
unused .
- If S is
- If the binding for N in envRec is a strict binding, set S to
true . - If the binding for N in envRec has not yet been initialized, then
- Throw a
ReferenceError exception.
- Throw a
- Else if the binding for N in envRec is a mutable binding, then
- Change its bound value to V.
- Else,
Assert : This is an attempt to change the value of an immutable binding.- If S is
true , throw aTypeError exception.
- Return
unused .
An example of ECMAScript code that results in a missing binding at step
function f() { eval("var x; x = (delete x, 0);"); }9.1.1.1.6 GetBindingValue ( N, S )
The GetBindingValue concrete method of a
Assert : envRec has a binding for N.- If the binding for N in envRec is an uninitialized binding, throw a
ReferenceError exception. - Return the value currently bound to N in envRec.
9.1.1.1.7 DeleteBinding ( N )
The DeleteBinding concrete method of a
Assert : envRec has a binding for N.- If the binding for N in envRec cannot be deleted, return
false . - Remove the binding for N from envRec.
- Return
true .
9.1.1.1.8 HasThisBinding ( )
The HasThisBinding concrete method of a
- Return
false .
A regular this binding.
9.1.1.1.9 HasSuperBinding ( )
The HasSuperBinding concrete method of a
- Return
false .
A regular super binding.
9.1.1.1.10 WithBaseObject ( )
The WithBaseObject concrete method of a
- Return
undefined .
9.1.1.2 Object Environment Records
Each Object Environment Record is associated with an object called its binding object. An Object Environment Record binds the set of string identifier names that directly correspond to the property names of its binding object.
Object Environment Records created for with statements (
Object Environment Records have the additional state fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[BindingObject]] | an Object |
The binding object of this |
| [[IsWithEnvironment]] | a Boolean |
Indicates whether this with statement.
|
9.1.1.2.1 HasBinding ( N )
The HasBinding concrete method of an
- Let bindingObject be envRec.[[BindingObject]].
- Let foundBinding be ?
HasProperty (bindingObject, N). - If foundBinding is
false , returnfalse . - If envRec.[[IsWithEnvironment]] is
false , returntrue . - Let unscopables be ?
Get (bindingObject,%Symbol.unscopables% ). - If unscopables
is an Object , then - Return
true .
9.1.1.2.2 CreateMutableBinding ( N, D )
The CreateMutableBinding concrete method of an
- Let bindingObject be envRec.[[BindingObject]].
- Perform ?
DefinePropertyOrThrow (bindingObject, N, PropertyDescriptor { [[Value]]:undefined , [[Writable]]:true , [[Enumerable]]:true , [[Configurable]]: D }). - Return
unused .
Normally envRec will not have a binding for N but if it does, the semantics of
9.1.1.2.3 CreateImmutableBinding ( N, S )
The CreateImmutableBinding concrete method of an
9.1.1.2.4 InitializeBinding ( N, V )
The InitializeBinding concrete method of an
- Perform ? envRec.SetMutableBinding(N, V,
false ). - Return
unused .
In this specification, all uses of CreateMutableBinding for
9.1.1.2.5 SetMutableBinding ( N, V, S )
The SetMutableBinding concrete method of an
- Let bindingObject be envRec.[[BindingObject]].
- Let stillExists be ?
HasProperty (bindingObject, N). - If stillExists is
false and S istrue , throw aReferenceError exception. - Perform ?
Set (bindingObject, N, V, S). - Return
unused .
9.1.1.2.6 GetBindingValue ( N, S )
The GetBindingValue concrete method of an
- Let bindingObject be envRec.[[BindingObject]].
- Let value be ?
HasProperty (bindingObject, N). - If value is
false , then- If S is
false , returnundefined ; otherwise throw aReferenceError exception.
- If S is
- Return ?
Get (bindingObject, N).
9.1.1.2.7 DeleteBinding ( N )
The DeleteBinding concrete method of an
- Let bindingObject be envRec.[[BindingObject]].
- Return ? bindingObject.[[Delete]](N).
9.1.1.2.8 HasThisBinding ( )
The HasThisBinding concrete method of an
- Return
false .
this binding.
9.1.1.2.9 HasSuperBinding ( )
The HasSuperBinding concrete method of an
- Return
false .
super binding.
9.1.1.2.10 WithBaseObject ( )
The WithBaseObject concrete method of an
- If envRec.[[IsWithEnvironment]] is
true , return envRec.[[BindingObject]]. - Otherwise, return
undefined .
9.1.1.3 Function Environment Records
A Function Environment Record is a this binding. If a function is not an super, its Function Environment Record also contains the state that is used to perform super method invocations from within the function.
Function Environment Records have the additional state fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[ThisValue]] |
an |
This is the |
| [[ThisBindingStatus]] |
|
If the value is |
| [[FunctionObject]] |
an ECMAScript |
The |
| [[NewTarget]] |
a |
If this |
Function Environment Records support all of the
| Method | Purpose |
|---|---|
| GetThisBinding() |
Return the value of this this binding. Throws a this binding has not been initialized.
|
9.1.1.3.1 BindThisValue ( envRec, V )
The abstract operation BindThisValue takes arguments envRec (a
Assert : envRec.[[ThisBindingStatus]] is notlexical .- If envRec.[[ThisBindingStatus]] is
initialized , throw aReferenceError exception. - Set envRec.[[ThisValue]] to V.
- Set envRec.[[ThisBindingStatus]] to
initialized . - Return
unused .
9.1.1.3.2 HasThisBinding ( )
The HasThisBinding concrete method of a
- If envRec.[[ThisBindingStatus]] is
lexical , returnfalse ; otherwise, returntrue .
9.1.1.3.3 HasSuperBinding ( )
The HasSuperBinding concrete method of a
- If envRec.[[ThisBindingStatus]] is
lexical , returnfalse . - If envRec.[[FunctionObject]].[[HomeObject]] is
undefined , returnfalse ; otherwise, returntrue .
9.1.1.3.4 GetThisBinding ( )
The GetThisBinding concrete method of a
Assert : envRec.[[ThisBindingStatus]] is notlexical .- If envRec.[[ThisBindingStatus]] is
uninitialized , throw aReferenceError exception. - Return envRec.[[ThisValue]].
9.1.1.3.5 GetSuperBase ( envRec )
The abstract operation GetSuperBase takes argument envRec (a super property accesses bound in envRec. The value
- Let home be envRec.[[FunctionObject]].[[HomeObject]].
- If home is
undefined , returnundefined . Assert : home is anordinary object .- Return ! home.[[GetPrototypeOf]]().
9.1.1.4 Global Environment Records
A Global Environment Record is used to represent the outer most scope that is shared by all of the ECMAScript
A Global Environment Record is logically a single record but it is specified as a composite encapsulating an
Properties may be created directly on a
Global Environment Records have the additional fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[ObjectRecord]] |
an |
Binding object is the |
| [[GlobalThisValue]] | an Object |
The value returned by this in global scope. |
| [[DeclarativeRecord]] |
a |
|
| Method | Purpose |
|---|---|
| GetThisBinding() |
Return the value of this this binding.
|
9.1.1.4.1 HasBinding ( N )
The HasBinding concrete method of a
- Let DclRec be envRec.[[DeclarativeRecord]].
- If ! DclRec.HasBinding(N) is
true , returntrue . - Let ObjRec be envRec.[[ObjectRecord]].
- Return ? ObjRec.HasBinding(N).
9.1.1.4.2 CreateMutableBinding ( N, D )
The CreateMutableBinding concrete method of a
- Let DclRec be envRec.[[DeclarativeRecord]].
- If ! DclRec.HasBinding(N) is
true , throw aTypeError exception. - Return ! DclRec.CreateMutableBinding(N, D).
9.1.1.4.3 CreateImmutableBinding ( N, S )
The CreateImmutableBinding concrete method of a
- Let DclRec be envRec.[[DeclarativeRecord]].
- If ! DclRec.HasBinding(N) is
true , throw aTypeError exception. - Return ! DclRec.CreateImmutableBinding(N, S).
9.1.1.4.4 InitializeBinding ( N, V )
The InitializeBinding concrete method of a
- Let DclRec be envRec.[[DeclarativeRecord]].
- If ! DclRec.HasBinding(N) is
true , then- Return ! DclRec.InitializeBinding(N, V).
Assert : If the binding exists, it must be in theObject Environment Record .- Let ObjRec be envRec.[[ObjectRecord]].
- Return ? ObjRec.InitializeBinding(N, V).
9.1.1.4.5 SetMutableBinding ( N, V, S )
The SetMutableBinding concrete method of a
- Let DclRec be envRec.[[DeclarativeRecord]].
- If ! DclRec.HasBinding(N) is
true , then- Return ? DclRec.SetMutableBinding(N, V, S).
- Let ObjRec be envRec.[[ObjectRecord]].
- Return ? ObjRec.SetMutableBinding(N, V, S).
9.1.1.4.6 GetBindingValue ( N, S )
The GetBindingValue concrete method of a
- Let DclRec be envRec.[[DeclarativeRecord]].
- If ! DclRec.HasBinding(N) is
true , then- Return ? DclRec.GetBindingValue(N, S).
- Let ObjRec be envRec.[[ObjectRecord]].
- Return ? ObjRec.GetBindingValue(N, S).
9.1.1.4.7 DeleteBinding ( N )
The DeleteBinding concrete method of a
- Let DclRec be envRec.[[DeclarativeRecord]].
- If ! DclRec.HasBinding(N) is
true , then- Return ! DclRec.DeleteBinding(N).
- Let ObjRec be envRec.[[ObjectRecord]].
- Let globalObject be ObjRec.[[BindingObject]].
- Let existingProp be ?
HasOwnProperty (globalObject, N). - If existingProp is
true , then- Return ? ObjRec.DeleteBinding(N).
- Return
true .
9.1.1.4.8 HasThisBinding ( )
The HasThisBinding concrete method of a
- Return
true .
this binding.
9.1.1.4.9 HasSuperBinding ( )
The HasSuperBinding concrete method of a
- Return
false .
super binding.
9.1.1.4.10 WithBaseObject ( )
The WithBaseObject concrete method of a
- Return
undefined .
9.1.1.4.11 GetThisBinding ( )
The GetThisBinding concrete method of a
- Return envRec.[[GlobalThisValue]].
9.1.1.4.12 HasLexicalDeclaration ( envRec, N )
The abstract operation HasLexicalDeclaration takes arguments envRec (a
- Let DclRec be envRec.[[DeclarativeRecord]].
- Return ! DclRec.HasBinding(N).
9.1.1.4.13 HasRestrictedGlobalProperty ( envRec, N )
The abstract operation HasRestrictedGlobalProperty takes arguments envRec (a
- Let ObjRec be envRec.[[ObjectRecord]].
- Let globalObject be ObjRec.[[BindingObject]].
- Let existingProp be ? globalObject.[[GetOwnProperty]](N).
- If existingProp is
undefined , returnfalse . - If existingProp.[[Configurable]] is
true , returnfalse . - Return
true .
Properties may exist upon a
9.1.1.4.14 CanDeclareGlobalVar ( envRec, N )
The abstract operation CanDeclareGlobalVar takes arguments envRec (a
- Let ObjRec be envRec.[[ObjectRecord]].
- Let globalObject be ObjRec.[[BindingObject]].
- Let hasProperty be ?
HasOwnProperty (globalObject, N). - If hasProperty is
true , returntrue . - Return ?
IsExtensible (globalObject).
9.1.1.4.15 CanDeclareGlobalFunction ( envRec, N )
The abstract operation CanDeclareGlobalFunction takes arguments envRec (a
- Let ObjRec be envRec.[[ObjectRecord]].
- Let globalObject be ObjRec.[[BindingObject]].
- Let existingProp be ? globalObject.[[GetOwnProperty]](N).
- If existingProp is
undefined , return ?IsExtensible (globalObject). - If existingProp.[[Configurable]] is
true , returntrue . - If
IsDataDescriptor (existingProp) istrue and existingProp has attribute values { [[Writable]]:true , [[Enumerable]]:true }, returntrue . - Return
false .
9.1.1.4.16 CreateGlobalVarBinding ( envRec, N, D )
The abstract operation CreateGlobalVarBinding takes arguments envRec (a
- Let ObjRec be envRec.[[ObjectRecord]].
- Let globalObject be ObjRec.[[BindingObject]].
- Let hasProperty be ?
HasOwnProperty (globalObject, N). - Let extensible be ?
IsExtensible (globalObject). - If hasProperty is
false and extensible istrue , then- Perform ? ObjRec.CreateMutableBinding(N, D).
- Perform ? ObjRec.InitializeBinding(N,
undefined ).
- Return
unused .
9.1.1.4.17 CreateGlobalFunctionBinding ( envRec, N, V, D )
The abstract operation CreateGlobalFunctionBinding takes arguments envRec (a
- Let ObjRec be envRec.[[ObjectRecord]].
- Let globalObject be ObjRec.[[BindingObject]].
- Let existingProp be ? globalObject.[[GetOwnProperty]](N).
- If existingProp is
undefined or existingProp.[[Configurable]] istrue , then- Let desc be the PropertyDescriptor { [[Value]]: V, [[Writable]]:
true , [[Enumerable]]:true , [[Configurable]]: D }.
- Let desc be the PropertyDescriptor { [[Value]]: V, [[Writable]]:
- Else,
- Let desc be the PropertyDescriptor { [[Value]]: V }.
- Perform ?
DefinePropertyOrThrow (globalObject, N, desc). - Perform ?
Set (globalObject, N, V,false ). - Return
unused .
Global function declarations are always represented as own properties of the
9.1.1.5 Module Environment Records
A Module Environment Record is a
Module Environment Records support all of the
| Method | Purpose |
|---|---|
| GetThisBinding() |
Return the value of this this binding.
|
9.1.1.5.1 GetBindingValue ( N, S )
The GetBindingValue concrete method of a
Assert : S istrue .Assert : envRec has a binding for N.- If the binding for N is an indirect binding, then
- Let M and N2 be the indirection values provided when this binding for N was created.
- Let targetEnv be M.[[Environment]].
- If targetEnv is
empty , throw aReferenceError exception. - Return ? targetEnv.GetBindingValue(N2,
true ).
- If the binding for N in envRec is an uninitialized binding, throw a
ReferenceError exception. - Return the value currently bound to N in envRec.
S will always be
9.1.1.5.2 DeleteBinding ( N )
The DeleteBinding concrete method of a
9.1.1.5.3 HasThisBinding ( )
The HasThisBinding concrete method of a
- Return
true .
this binding.
9.1.1.5.4 GetThisBinding ( )
The GetThisBinding concrete method of a
- Return
undefined .
9.1.1.5.5 CreateImportBinding ( envRec, N, M, N2 )
The abstract operation CreateImportBinding takes arguments envRec (a
9.1.2 Environment Record Operations
The following
9.1.2.1 GetIdentifierReference ( env, name, strict )
The abstract operation GetIdentifierReference takes arguments env (an
- If env is
null , then- Return the
Reference Record { [[Base]]:unresolvable , [[ReferencedName]]: name, [[Strict]]: strict, [[ThisValue]]:empty }.
- Return the
- Let exists be ? env.HasBinding(name).
- If exists is
true , then- Return the
Reference Record { [[Base]]: env, [[ReferencedName]]: name, [[Strict]]: strict, [[ThisValue]]:empty }.
- Return the
- Else,
- Let outer be env.[[OuterEnv]].
- Return ?
GetIdentifierReference (outer, name, strict).
9.1.2.2 NewDeclarativeEnvironment ( E )
The abstract operation NewDeclarativeEnvironment takes argument E (an
- Let env be a new
Declarative Environment Record containing no bindings. - Set env.[[OuterEnv]] to E.
- Return env.
9.1.2.3 NewObjectEnvironment ( O, W, E )
The abstract operation NewObjectEnvironment takes arguments O (an Object), W (a Boolean), and E (an
- Let env be a new
Object Environment Record . - Set env.[[BindingObject]] to O.
- Set env.[[IsWithEnvironment]] to W.
- Set env.[[OuterEnv]] to E.
- Return env.
9.1.2.4 NewFunctionEnvironment ( F, newTarget )
The abstract operation NewFunctionEnvironment takes arguments F (an ECMAScript
- Let env be a new
Function Environment Record containing no bindings. - Set env.[[FunctionObject]] to F.
- If F.[[ThisMode]] is
lexical , set env.[[ThisBindingStatus]] tolexical . - Else, set env.[[ThisBindingStatus]] to
uninitialized . - Set env.[[NewTarget]] to newTarget.
- Set env.[[OuterEnv]] to F.[[Environment]].
- Return env.
9.1.2.5 NewGlobalEnvironment ( G, thisValue )
The abstract operation NewGlobalEnvironment takes arguments G (an Object) and thisValue (an Object) and returns a
- Let objRec be
NewObjectEnvironment (G,false ,null ). - Let dclRec be
NewDeclarativeEnvironment (null ). - Let env be a new
Global Environment Record . - Set env.[[ObjectRecord]] to objRec.
- Set env.[[GlobalThisValue]] to thisValue.
- Set env.[[DeclarativeRecord]] to dclRec.
- Set env.[[OuterEnv]] to
null . - Return env.
9.1.2.6 NewModuleEnvironment ( E )
The abstract operation NewModuleEnvironment takes argument E (an
- Let env be a new
Module Environment Record containing no bindings. - Set env.[[OuterEnv]] to E.
- Return env.
9.2 PrivateEnvironment Records
A PrivateEnvironment Record is a specification mechanism used to track
Each
| Field Name | Value Type | Meaning |
|---|---|---|
| [[OuterPrivateEnvironment]] |
a |
The |
| [[Names]] |
a |
The |
9.2.1 PrivateEnvironment Record Operations
The following
9.2.1.1 NewPrivateEnvironment ( outerPrivateEnv )
The abstract operation NewPrivateEnvironment takes argument outerPrivateEnv (a
- Let names be a new empty
List . - Return the
PrivateEnvironment Record { [[OuterPrivateEnvironment]]: outerPrivateEnv, [[Names]]: names }.
9.2.1.2 ResolvePrivateIdentifier ( privateEnv, identifier )
The abstract operation ResolvePrivateIdentifier takes arguments privateEnv (a
- Let names be privateEnv.[[Names]].
- For each
Private Name pn of names, do- If pn.[[Description]] is identifier, then
- Return pn.
- If pn.[[Description]] is identifier, then
- Let outerPrivateEnv be privateEnv.[[OuterPrivateEnvironment]].
Assert : outerPrivateEnv is notnull .- Return
ResolvePrivateIdentifier (outerPrivateEnv, identifier).
9.3 Realms
Before it is evaluated, all ECMAScript code must be associated with a realm. Conceptually, a
A
| Field Name | Value | Meaning |
|---|---|---|
| [[AgentSignifier]] |
an |
The |
| [[Intrinsics]] |
a |
The intrinsic values used by code associated with this |
| [[GlobalObject]] | an Object |
The |
| [[GlobalEnv]] |
a |
The global environment for this |
| [[TemplateMap]] |
a |
Template objects are canonicalized separately for each Once a |
| [[LoadedModules]] |
a |
A map from the specifier strings imported by this
As mentioned in import() expression in a context where there is no |
| [[HostDefined]] |
anything (default value is |
Field reserved for use by |
9.3.1 InitializeHostDefinedRealm ( )
The abstract operation InitializeHostDefinedRealm takes no arguments and returns either a
- Let realm be a new
Realm Record . - Perform
CreateIntrinsics (realm). - Set realm.[[AgentSignifier]] to
AgentSignifier (). - Set realm.[[TemplateMap]] to a new empty
List . - Let newContext be a new
execution context . - Set the Function of newContext to
null . - Set the
Realm of newContext to realm. - Set the ScriptOrModule of newContext to
null . - Push newContext onto the
execution context stack ; newContext is now therunning execution context . - If the
host requires use of anexotic object to serve as realm'sglobal object , then- Let global be such an object created in a
host-defined manner.
- Let global be such an object created in a
- Else,
- Let global be
OrdinaryObjectCreate (realm.[[Intrinsics]].[[%Object.prototype% ]]).
- Let global be
- If the
host requires that thethisbinding in realm's global scope return an object other than theglobal object , then- Let thisValue be such an object created in a
host-defined manner.
- Let thisValue be such an object created in a
- Else,
- Let thisValue be global.
- Set realm.[[GlobalObject]] to global.
- Set realm.[[GlobalEnv]] to
NewGlobalEnvironment (global, thisValue). - Perform ?
SetDefaultGlobalBindings (realm). - Create any
host-defined global object properties on global. - Return
unused .
9.3.2 CreateIntrinsics ( realmRec )
The abstract operation CreateIntrinsics takes argument realmRec (a
- Set realmRec.[[Intrinsics]] to a new
Record . - Set fields of realmRec.[[Intrinsics]] with the values listed in
Table 6 . The field names are the names listed in column one of the table. The value of each field is a new object value fully and recursively populated with property values as defined by the specification of each object in clauses19 through28 . All object property values are newly created object values. All values that are built-infunction objects are created by performingCreateBuiltinFunction (steps, length, name, slots, realmRec, prototype) where steps is the definition of that function provided by this specification, name is the initial value of the function's"name" property, length is the initial value of the function's"length" property, slots is a list of the names, if any, of the function's specified internal slots, and prototype is the specified value of the function's [[Prototype]] internal slot. The creation of the intrinsics and their properties must be ordered to avoid any dependencies upon objects that have not yet been created. - Perform
AddRestrictedFunctionProperties (realmRec.[[Intrinsics]].[[%Function.prototype% ]], realmRec). - Return
unused .
9.3.3 SetDefaultGlobalBindings ( realmRec )
The abstract operation SetDefaultGlobalBindings takes argument realmRec (a
- Let global be realmRec.[[GlobalObject]].
- For each property of the Global Object specified in clause
19 , do- Let name be the String value of the
property name . - Let desc be the fully populated data
Property Descriptor for the property, containing the specified attributes for the property. For properties listed in19.2 ,19.3 , or19.4 the value of the [[Value]] attribute is the corresponding intrinsic object from realmRec. - Perform ?
DefinePropertyOrThrow (global, name, desc).
- Let name be the String value of the
- Return
unused .
9.4 Execution Contexts
An execution context is a specification device that is used to track the runtime evaluation of code by an ECMAScript implementation. At any point in time, there is at most one execution context per
The execution context stack is used to track execution contexts. The
An execution context contains whatever implementation specific state is necessary to track the execution progress of its associated code. Each execution context has at least the state components listed in
| Component | Purpose |
|---|---|
| code evaluation state |
Any state needed to perform, suspend, and resume evaluation of the code associated with this |
| Function |
If this |
|
|
The |
| ScriptOrModule |
The |
The value of the
ECMAScript code execution contexts have the additional state components listed in
| Component | Purpose |
|---|---|
| LexicalEnvironment |
Identifies the |
| VariableEnvironment |
Identifies the |
| PrivateEnvironment |
Identifies the |
The LexicalEnvironment and VariableEnvironment components of an execution context are always
Execution contexts representing the evaluation of Generators have the additional state components listed in
| Component | Purpose |
|---|---|
| Generator |
The Generator that this |
In most situations only the
An execution context is purely a specification mechanism and need not correspond to any particular artefact of an ECMAScript implementation. It is impossible for ECMAScript code to directly access or observe an execution context.
9.4.1 GetActiveScriptOrModule ( )
The abstract operation GetActiveScriptOrModule takes no arguments and returns a
- If the
execution context stack is empty, returnnull . - Let ec be the topmost
execution context on theexecution context stack whose ScriptOrModule component is notnull . - If no such
execution context exists, returnnull . Otherwise, return ec's ScriptOrModule.
9.4.2 ResolveBinding ( name [ , env ] )
The abstract operation ResolveBinding takes argument name (a String) and optional argument env (an
- If env is not present or env is
undefined , then- Set env to the
running execution context 's LexicalEnvironment.
- Set env to the
Assert : env is anEnvironment Record .- Let strict be
IsStrict (the syntactic production that is being evaluated). - Return ?
GetIdentifierReference (env, name, strict).
The result of ResolveBinding is always a
9.4.3 GetThisEnvironment ( )
The abstract operation GetThisEnvironment takes no arguments and returns an this. It performs the following steps when called:
- Let env be the
running execution context 's LexicalEnvironment. - Repeat,
- Let exists be env.HasThisBinding().
- If exists is
true , return env. - Let outer be env.[[OuterEnv]].
Assert : outer is notnull .- Set env to outer.
The loop in step this binding.
9.4.4 ResolveThisBinding ( )
The abstract operation ResolveThisBinding takes no arguments and returns either a this using the LexicalEnvironment of the
- Let envRec be
GetThisEnvironment (). - Return ? envRec.GetThisBinding().
9.4.5 GetNewTarget ( )
The abstract operation GetNewTarget takes no arguments and returns an Object or
- Let envRec be
GetThisEnvironment (). Assert : envRec has a [[NewTarget]] field.- Return envRec.[[NewTarget]].
9.4.6 GetGlobalObject ( )
The abstract operation GetGlobalObject takes no arguments and returns an Object. It returns the
- Let currentRealm be
the current Realm Record . - Return currentRealm.[[GlobalObject]].
9.5 Jobs and Host Operations to Enqueue Jobs
A Job is an
- At some future point in time, when there is no running context in the
agent for which the job is scheduled and thatagent 'sexecution context stack is empty, the implementation must:- Perform any
host-defined preparation steps. Invoke theJob Abstract Closure .- Perform any
host-defined cleanup steps, after which theexecution context stack must be empty.
- Perform any
- Only one
Job may be actively undergoing evaluation at any point in time in anagent . - Once evaluation of a
Job starts, it must run to completion before evaluation of any otherJob starts in anagent . - The
Abstract Closure must return anormal completion , implementing its own handling of errors.
At any particular time, scriptOrModule (a
GetActiveScriptOrModule () is scriptOrModule.- If scriptOrModule is a
Script Record orModule Record , let ec be the topmostexecution context on theexecution context stack whose ScriptOrModule component is scriptOrModule. TheRealm component of ec is scriptOrModule.[[Realm]].
At any particular time, an execution is prepared to evaluate ECMAScript code if all of the following conditions are true:
- The
execution context stack is not empty. - The
Realm component of the topmostexecution context on theexecution context stack is aRealm Record .
The specific choice of
Particular kinds of
9.5.1 JobCallback Records
A JobCallback Record is a
The WHATWG HTML specification (https://html.spec.whatwg.org/), for example, uses the
JobCallback Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Callback]] |
a |
The function to invoke when the |
| [[HostDefined]] |
anything (default value is |
Field reserved for use by |
9.5.2 HostMakeJobCallback ( callback )
The
An implementation of HostMakeJobCallback must conform to the following requirements:
- It must return a
JobCallback Record whose [[Callback]] field is callback.
The default implementation of HostMakeJobCallback performs the following steps when called:
- Return the
JobCallback Record { [[Callback]]: callback, [[HostDefined]]:empty }.
ECMAScript
This is called at the time that the callback is passed to the function that is responsible for its being eventually scheduled and run. For example, promise.then(thenAction) calls MakeJobCallback on thenAction at the time of invoking Promise.prototype.then, not at the time of scheduling the reaction
9.5.3 HostCallJobCallback ( jobCallback, V, argumentsList )
The
An implementation of HostCallJobCallback must conform to the following requirements:
- It must perform and return the result of
Call (jobCallback.[[Callback]], V, argumentsList).
This requirement means that
The default implementation of HostCallJobCallback performs the following steps when called:
Assert :IsCallable (jobCallback.[[Callback]]) istrue .- Return ?
Call (jobCallback.[[Callback]], V, argumentsList).
ECMAScript
9.5.4 HostEnqueueGenericJob ( job, realm )
The
An implementation of HostEnqueueGenericJob must conform to the requirements in
9.5.5 HostEnqueuePromiseJob ( job, realm )
The
An implementation of HostEnqueuePromiseJob must conform to the requirements in
- If realm is not
null , each time job is invoked the implementation must performimplementation-defined steps such that execution isprepared to evaluate ECMAScript code at the time of job's invocation. - Let scriptOrModule be
GetActiveScriptOrModule () at the time HostEnqueuePromiseJob is invoked. If realm is notnull , each time job is invoked the implementation must performimplementation-defined steps such that scriptOrModule is theactive script or module at the time of job's invocation. Jobs must run in the same order as the HostEnqueuePromiseJob invocations that scheduled them.
The realm for
9.5.6 HostEnqueueTimeoutJob ( timeoutJob, realm, milliseconds )
The
An implementation of HostEnqueueTimeoutJob must conform to the requirements in
9.6 Agents
An agent comprises a set of ECMAScript
An
Some web browsers share a single
While an
An agent signifier is a globally-unique opaque value used to identify an
| Field Name | Value | Meaning |
|---|---|---|
| [[LittleEndian]] | a Boolean | The default value computed for the isLittleEndian parameter when it is needed by the algorithms |
| [[CanBlock]] | a Boolean | Determines whether the |
| [[Signifier]] | an |
Uniquely identifies the |
| [[IsLockFree1]] | a Boolean | |
| [[IsLockFree2]] | a Boolean | |
| [[IsLockFree8]] | a Boolean | |
| [[CandidateExecution]] | a |
See the |
| [[KeptAlive]] | a |
Initially a new empty |
| [[ModuleAsyncEvaluationCount]] | an |
Initially 0, used to assign unique incrementing values to the [[AsyncEvaluationOrder]] field of modules that are asynchronous or have asynchronous dependencies. |
Once the values of [[Signifier]], [[IsLockFree1]], and [[IsLockFree2]] have been observed by any
The values of [[IsLockFree1]] and [[IsLockFree2]] are not necessarily determined by the hardware, but may also reflect implementation choices that can vary over time and between ECMAScript implementations.
There is no [[IsLockFree4]] field: 4-byte atomic operations are always lock-free.
In practice, if an atomic operation is implemented with any type of lock the operation is not lock-free. Lock-free does not imply wait-free: there is no upper bound on how many machine steps may be required to complete a lock-free atomic operation.
That an atomic access of size n is lock-free does not imply anything about the (perceived) atomicity of non-atomic accesses of size n, specifically, non-atomic accesses may still be performed as a sequence of several separate memory accesses. See
An
9.6.1 AgentSignifier ( )
The abstract operation AgentSignifier takes no arguments and returns an
- Let AR be the
Agent Record of thesurrounding agent . - Return AR.[[Signifier]].
9.6.2 AgentCanSuspend ( )
The abstract operation AgentCanSuspend takes no arguments and returns a Boolean. It performs the following steps when called:
- Let AR be the
Agent Record of thesurrounding agent . - Return AR.[[CanBlock]].
In some environments it may not be reasonable for a given
9.6.3 IncrementModuleAsyncEvaluationCount ( )
The abstract operation IncrementModuleAsyncEvaluationCount takes no arguments and returns an
- Let AR be the
Agent Record of thesurrounding agent . - Let count be AR.[[ModuleAsyncEvaluationCount]].
- Set AR.[[ModuleAsyncEvaluationCount]] to count + 1.
- Return count.
This value is only used to keep track of the relative evaluation order between pending modules. An implementation may unobservably reset [[ModuleAsyncEvaluationCount]] to 0 whenever there are no pending modules.
9.7 Agent Clusters
An agent cluster is a maximal set of
Programs within different
There may be
Every
All
If different
All
All
An embedding may deactivate (stop forward progress) or activate (resume forward progress) an
The purpose of the preceding restriction is to avoid a situation where an
The implication of the restriction is that it will not be possible to share memory between
An embedding may terminate an
Each of the following specification values, and values transitively reachable from them, belong to exactly one agent cluster.
Prior to any evaluation of any ECMAScript code by any
All
An agent cluster is a specification mechanism and need not correspond to any particular artefact of an ECMAScript implementation.
9.8 Forward Progress
For an
An
Implementations must ensure that:
- every unblocked
agent with a dedicatedexecuting thread eventually makes forward progress - in a set of
agents that share anexecuting thread , oneagent eventually makes forward progress - an
agent does not cause anotheragent to become blocked except via explicit APIs that provide blocking.
This, along with the liveness guarantee in the
9.9 Processing Model of WeakRef and FinalizationRegistry Targets
9.9.1 Objectives
This specification does not make any guarantees that any object or symbol will be garbage collected. Objects or symbols which are not
The semantics of
-
When
WeakRef.prototype.derefis called, the referent (ifundefined is not returned) is kept alive so that subsequent, synchronous accesses also return the same value. This list is reset when synchronous work is done using theClearKeptObjects abstract operation. -
When an object or symbol which is registered with a
FinalizationRegistry becomes unreachable, a call of theFinalizationRegistry 's cleanup callback may eventually be made, after synchronous ECMAScript execution completes. TheFinalizationRegistry cleanup is performed with theCleanupFinalizationRegistry abstract operation.
Neither of these actions (
Some ECMAScript implementations include garbage collector implementations which run in the background, including when ECMAScript is idle. Letting the
9.9.2 Liveness
For some set of objects and/or symbols S a hypothetical WeakRef-oblivious execution with respect to S is an execution whereby the abstract operation
At any point during evaluation, a set of objects and/or symbols S is considered live if either of the following conditions is met:
-
Any element in S is included in any
agent 's [[KeptAlive]]List . - There exists a valid future hypothetical WeakRef-oblivious execution with respect to S that observes the identity of any value in S.
Presence of an object or a symbol in a field, an internal slot, or a property does not imply that the value is live. For example if the value in question is never passed back to the program, then it cannot be observed.
This is the case for keys in a WeakMap, members of a WeakSet, as well as the [[WeakRefTarget]] and [[UnregisterToken]] fields of a
The above definition implies that, if a key in a WeakMap is not live, then its corresponding value is not necessarily live either.
9.9.3 Execution
At any time, if a set of objects and/or symbols S is not
- For each element value of S, do
- For each
WeakRef ref such that ref.[[WeakRefTarget]] is value, do- Set ref.[[WeakRefTarget]] to
empty .
- Set ref.[[WeakRefTarget]] to
- For each
FinalizationRegistry fg such that fg.[[Cells]] contains aRecord cell such that cell.[[WeakRefTarget]] is value, do- Set cell.[[WeakRefTarget]] to
empty . - Optionally, perform
HostEnqueueFinalizationRegistryCleanupJob (fg).
- Set cell.[[WeakRefTarget]] to
- For each WeakMap map such that map.[[WeakMapData]] contains a
Record r such that r.[[Key]] is value, do- Set r.[[Key]] to
empty . - Set r.[[Value]] to
empty .
- Set r.[[Key]] to
- For each WeakSet set such that set.[[WeakSetData]] contains value, do
- Replace the element of set.[[WeakSetData]] whose value is value with an element whose value is
empty .
- Replace the element of set.[[WeakSetData]] whose value is value with an element whose value is
- For each
Together with the definition of liveness, this clause prescribes optimizations that an implementation may apply regarding
It is possible to access an object without observing its identity. Optimizations such as dead variable elimination and scalar replacement on properties of non-escaping objects whose identity is not observed are allowed. These optimizations are thus allowed to observably empty
On the other hand, if an object's identity is observable, and that object is in the [[WeakRefTarget]] internal slot of a
Because calling
Implementations are not obligated to empty
If an implementation chooses a non-
9.9.4 Host Hooks
9.9.4.1 HostEnqueueFinalizationRegistryCleanupJob ( finalizationRegistry )
The
Let cleanupJob be a new
- Let cleanupResult be
Completion (CleanupFinalizationRegistry (finalizationRegistry)). - If cleanupResult is an
abrupt completion , perform anyhost-defined steps for reporting the error. - Return
unused .
An implementation of HostEnqueueFinalizationRegistryCleanupJob schedules cleanupJob to be performed at some future time, if possible. It must also conform to the requirements in
9.10 ClearKeptObjects ( )
The abstract operation ClearKeptObjects takes no arguments and returns
- Let agentRecord be the
surrounding agent 'sAgent Record . - Set agentRecord.[[KeptAlive]] to a new empty
List . - Return
unused .
9.11 AddToKeptObjects ( value )
The abstract operation AddToKeptObjects takes argument value (an Object or a Symbol) and returns
- Let agentRecord be the
surrounding agent 'sAgent Record . - Append value to agentRecord.[[KeptAlive]].
- Return
unused .
9.12 CleanupFinalizationRegistry ( finalizationRegistry )
The abstract operation CleanupFinalizationRegistry takes argument finalizationRegistry (a
Assert : finalizationRegistry has [[Cells]] and [[CleanupCallback]] internal slots.- Let callback be finalizationRegistry.[[CleanupCallback]].
- While finalizationRegistry.[[Cells]] contains a
Record cell such that cell.[[WeakRefTarget]] isempty , an implementation may perform the following steps:- Choose any such cell.
- Remove cell from finalizationRegistry.[[Cells]].
- Perform ?
HostCallJobCallback (callback,undefined , « cell.[[HeldValue]] »).
- Return
unused .
9.13 CanBeHeldWeakly ( v )
The abstract operation CanBeHeldWeakly takes argument v (an
- If v
is an Object , returntrue . - If v
is a Symbol andKeyForSymbol (v) isundefined , returntrue . - Return
false .
A language value without
10 Ordinary and Exotic Objects Behaviours
10.1 Ordinary Object Internal Methods and Internal Slots
All
Every
In the following algorithm descriptions, assume O is an
Each
10.1.1 [[GetPrototypeOf]] ( )
The [[GetPrototypeOf]] internal method of an
- Return
OrdinaryGetPrototypeOf (O).
10.1.1.1 OrdinaryGetPrototypeOf ( O )
The abstract operation OrdinaryGetPrototypeOf takes argument O (an Object) and returns an Object or
- Return O.[[Prototype]].
10.1.2 [[SetPrototypeOf]] ( V )
The [[SetPrototypeOf]] internal method of an
- Return
OrdinarySetPrototypeOf (O, V).
10.1.2.1 OrdinarySetPrototypeOf ( O, V )
The abstract operation OrdinarySetPrototypeOf takes arguments O (an Object) and V (an Object or
- Let current be O.[[Prototype]].
- If
SameValue (V, current) istrue , returntrue . - Let extensible be O.[[Extensible]].
- If extensible is
false , returnfalse . - Let p be V.
- Let done be
false . - Repeat, while done is
false ,- If p is
null , then- Set done to
true .
- Set done to
- Else if
SameValue (p, O) istrue , then- Return
false .
- Return
- Else,
- If p.[[GetPrototypeOf]] is not the
ordinary object internal method defined in10.1.1 , set done totrue . - Else, set p to p.[[Prototype]].
- If p.[[GetPrototypeOf]] is not the
- If p is
- Set O.[[Prototype]] to V.
- Return
true .
The loop in step
10.1.3 [[IsExtensible]] ( )
The [[IsExtensible]] internal method of an
- Return
OrdinaryIsExtensible (O).
10.1.3.1 OrdinaryIsExtensible ( O )
The abstract operation OrdinaryIsExtensible takes argument O (an Object) and returns a Boolean. It performs the following steps when called:
- Return O.[[Extensible]].
10.1.4 [[PreventExtensions]] ( )
The [[PreventExtensions]] internal method of an
- Return
OrdinaryPreventExtensions (O).
10.1.4.1 OrdinaryPreventExtensions ( O )
The abstract operation OrdinaryPreventExtensions takes argument O (an Object) and returns
- Set O.[[Extensible]] to
false . - Return
true .
10.1.5 [[GetOwnProperty]] ( P )
The [[GetOwnProperty]] internal method of an
- Return
OrdinaryGetOwnProperty (O, P).
10.1.5.1 OrdinaryGetOwnProperty ( O, P )
The abstract operation OrdinaryGetOwnProperty takes arguments O (an Object) and P (a
- If O does not have an own property with key P, return
undefined . - Let D be a newly created
Property Descriptor with no fields. - Let X be O's own property whose key is P.
- If X is a
data property , then- Set D.[[Value]] to the value of X's [[Value]] attribute.
- Set D.[[Writable]] to the value of X's [[Writable]] attribute.
- Else,
Assert : X is anaccessor property .- Set D.[[Get]] to the value of X's [[Get]] attribute.
- Set D.[[Set]] to the value of X's [[Set]] attribute.
- Set D.[[Enumerable]] to the value of X's [[Enumerable]] attribute.
- Set D.[[Configurable]] to the value of X's [[Configurable]] attribute.
- Return D.
10.1.6 [[DefineOwnProperty]] ( P, Desc )
The [[DefineOwnProperty]] internal method of an
- Return ?
OrdinaryDefineOwnProperty (O, P, Desc).
10.1.6.1 OrdinaryDefineOwnProperty ( O, P, Desc )
The abstract operation OrdinaryDefineOwnProperty takes arguments O (an Object), P (a
- Let current be ? O.[[GetOwnProperty]](P).
- Let extensible be ?
IsExtensible (O). - Return
ValidateAndApplyPropertyDescriptor (O, P, extensible, Desc, current).
10.1.6.2 IsCompatiblePropertyDescriptor ( Extensible, Desc, Current )
The abstract operation IsCompatiblePropertyDescriptor takes arguments Extensible (a Boolean), Desc (a
- Return
ValidateAndApplyPropertyDescriptor (undefined ,"" , Extensible, Desc, Current).
10.1.6.3 ValidateAndApplyPropertyDescriptor ( O, P, extensible, Desc, current )
The abstract operation ValidateAndApplyPropertyDescriptor takes arguments O (an Object or
Assert : P is aproperty key .- If current is
undefined , then- If extensible is
false , returnfalse . - If O is
undefined , returntrue . - If
IsAccessorDescriptor (Desc) istrue , then- Create an own
accessor property named P of object O whose [[Get]], [[Set]], [[Enumerable]], and [[Configurable]] attributes are set to the value of the corresponding field in Desc if Desc has that field, or to the attribute'sdefault value otherwise.
- Create an own
- Else,
- Create an own
data property named P of object O whose [[Value]], [[Writable]], [[Enumerable]], and [[Configurable]] attributes are set to the value of the corresponding field in Desc if Desc has that field, or to the attribute'sdefault value otherwise.
- Create an own
- Return
true .
- If extensible is
Assert : current is afully populated Property Descriptor .- If Desc does not have any fields, return
true . - If current.[[Configurable]] is
false , then- If Desc has a [[Configurable]] field and Desc.[[Configurable]] is
true , returnfalse . - If Desc has an [[Enumerable]] field and Desc.[[Enumerable]] is not current.[[Enumerable]], return
false . - If
IsGenericDescriptor (Desc) isfalse andIsAccessorDescriptor (Desc) is notIsAccessorDescriptor (current), returnfalse . - If
IsAccessorDescriptor (current) istrue , then - Else if current.[[Writable]] is
false , then- If Desc has a [[Writable]] field and Desc.[[Writable]] is
true , returnfalse . - NOTE:
SameValue returnstrue forNaN values which may be distinguishable by other means. Returning here ensures that any existing property of O remains unmodified. - If Desc has a [[Value]] field, return
SameValue (Desc.[[Value]], current.[[Value]]).
- If Desc has a [[Writable]] field and Desc.[[Writable]] is
- If Desc has a [[Configurable]] field and Desc.[[Configurable]] is
- If O is not
undefined , then- If
IsDataDescriptor (current) istrue andIsAccessorDescriptor (Desc) istrue , then- If Desc has a [[Configurable]] field, let configurable be Desc.[[Configurable]]; else let configurable be current.[[Configurable]].
- If Desc has a [[Enumerable]] field, let enumerable be Desc.[[Enumerable]]; else let enumerable be current.[[Enumerable]].
- Replace the property named P of object O with an
accessor property whose [[Configurable]] and [[Enumerable]] attributes are set to configurable and enumerable, respectively, and whose [[Get]] and [[Set]] attributes are set to the value of the corresponding field in Desc if Desc has that field, or to the attribute'sdefault value otherwise.
- Else if
IsAccessorDescriptor (current) istrue andIsDataDescriptor (Desc) istrue , then- If Desc has a [[Configurable]] field, let configurable be Desc.[[Configurable]]; else let configurable be current.[[Configurable]].
- If Desc has a [[Enumerable]] field, let enumerable be Desc.[[Enumerable]]; else let enumerable be current.[[Enumerable]].
- Replace the property named P of object O with a
data property whose [[Configurable]] and [[Enumerable]] attributes are set to configurable and enumerable, respectively, and whose [[Value]] and [[Writable]] attributes are set to the value of the corresponding field in Desc if Desc has that field, or to the attribute'sdefault value otherwise.
- Else,
- For each field of Desc, set the corresponding attribute of the property named P of object O to the value of the field.
- If
- Return
true .
10.1.7 [[HasProperty]] ( P )
The [[HasProperty]] internal method of an
- Return ?
OrdinaryHasProperty (O, P).
10.1.7.1 OrdinaryHasProperty ( O, P )
The abstract operation OrdinaryHasProperty takes arguments O (an Object) and P (a
- Let hasOwn be ? O.[[GetOwnProperty]](P).
- If hasOwn is not
undefined , returntrue . - Let parent be ? O.[[GetPrototypeOf]]().
- If parent is not
null , then- Return ? parent.[[HasProperty]](P).
- Return
false .
10.1.8 [[Get]] ( P, Receiver )
The [[Get]] internal method of an
- Return ?
OrdinaryGet (O, P, Receiver).
10.1.8.1 OrdinaryGet ( O, P, Receiver )
The abstract operation OrdinaryGet takes arguments O (an Object), P (a
- Let desc be ? O.[[GetOwnProperty]](P).
- If desc is
undefined , then- Let parent be ? O.[[GetPrototypeOf]]().
- If parent is
null , returnundefined . - Return ? parent.[[Get]](P, Receiver).
- If
IsDataDescriptor (desc) istrue , return desc.[[Value]]. Assert :IsAccessorDescriptor (desc) istrue .- Let getter be desc.[[Get]].
- If getter is
undefined , returnundefined . - Return ?
Call (getter, Receiver).
10.1.9 [[Set]] ( P, V, Receiver )
The [[Set]] internal method of an
- Return ?
OrdinarySet (O, P, V, Receiver).
10.1.9.1 OrdinarySet ( O, P, V, Receiver )
The abstract operation OrdinarySet takes arguments O (an Object), P (a
- Let ownDesc be ? O.[[GetOwnProperty]](P).
- Return ?
OrdinarySetWithOwnDescriptor (O, P, V, Receiver, ownDesc).
10.1.9.2 OrdinarySetWithOwnDescriptor ( O, P, V, Receiver, ownDesc )
The abstract operation OrdinarySetWithOwnDescriptor takes arguments O (an Object), P (a
- If ownDesc is
undefined , then- Let parent be ? O.[[GetPrototypeOf]]().
- If parent is not
null , then- Return ? parent.[[Set]](P, V, Receiver).
- Else,
- Set ownDesc to the PropertyDescriptor { [[Value]]:
undefined , [[Writable]]:true , [[Enumerable]]:true , [[Configurable]]:true }.
- Set ownDesc to the PropertyDescriptor { [[Value]]:
- If
IsDataDescriptor (ownDesc) istrue , then- If ownDesc.[[Writable]] is
false , returnfalse . - If Receiver
is not an Object , returnfalse . - Let existingDescriptor be ? Receiver.[[GetOwnProperty]](P).
- If existingDescriptor is not
undefined , then- If
IsAccessorDescriptor (existingDescriptor) istrue , returnfalse . - If existingDescriptor.[[Writable]] is
false , returnfalse . - Let valueDesc be the PropertyDescriptor { [[Value]]: V }.
- Return ? Receiver.[[DefineOwnProperty]](P, valueDesc).
- If
- Else,
Assert : Receiver does not currently have a property P.- Return ?
CreateDataProperty (Receiver, P, V).
- If ownDesc.[[Writable]] is
Assert :IsAccessorDescriptor (ownDesc) istrue .- Let setter be ownDesc.[[Set]].
- If setter is
undefined , returnfalse . - Perform ?
Call (setter, Receiver, « V »). - Return
true .
10.1.10 [[Delete]] ( P )
The [[Delete]] internal method of an
- Return ?
OrdinaryDelete (O, P).
10.1.10.1 OrdinaryDelete ( O, P )
The abstract operation OrdinaryDelete takes arguments O (an Object) and P (a
- Let desc be ? O.[[GetOwnProperty]](P).
- If desc is
undefined , returntrue . - If desc.[[Configurable]] is
true , then- Remove the own property with name P from O.
- Return
true .
- Return
false .
10.1.11 [[OwnPropertyKeys]] ( )
The [[OwnPropertyKeys]] internal method of an
- Return
OrdinaryOwnPropertyKeys (O).
10.1.11.1 OrdinaryOwnPropertyKeys ( O )
The abstract operation OrdinaryOwnPropertyKeys takes argument O (an Object) and returns a
- Let keys be a new empty
List . - For each own
property key P of O such that P is anarray index , in ascending numeric index order, do- Append P to keys.
- For each own
property key P of O such that Pis a String and P is not anarray index , in ascending chronological order of property creation, do- Append P to keys.
- For each own
property key P of O such that Pis a Symbol , in ascending chronological order of property creation, do- Append P to keys.
- Return keys.
10.1.12 OrdinaryObjectCreate ( proto [ , additionalInternalSlotsList ] )
The abstract operation OrdinaryObjectCreate takes argument proto (an Object or
- Let internalSlotsList be « [[Prototype]], [[Extensible]] ».
- If additionalInternalSlotsList is present, set internalSlotsList to the
list-concatenation of internalSlotsList and additionalInternalSlotsList. - Let O be
MakeBasicObject (internalSlotsList). - Set O.[[Prototype]] to proto.
- Return O.
Although OrdinaryObjectCreate does little more than call
10.1.13 OrdinaryCreateFromConstructor ( constructor, intrinsicDefaultProto [ , internalSlotsList ] )
The abstract operation OrdinaryCreateFromConstructor takes arguments constructor (a
Assert : intrinsicDefaultProto is this specification's name of an intrinsic object. The corresponding object must be an intrinsic that is intended to be used as the [[Prototype]] value of an object.- Let proto be ?
GetPrototypeFromConstructor (constructor, intrinsicDefaultProto). - If internalSlotsList is present, let slotsList be internalSlotsList.
- Else, let slotsList be a new empty
List . - Return
OrdinaryObjectCreate (proto, slotsList).
10.1.14 GetPrototypeFromConstructor ( constructor, intrinsicDefaultProto )
The abstract operation GetPrototypeFromConstructor takes arguments constructor (a
Assert : intrinsicDefaultProto is this specification's name of an intrinsic object. The corresponding object must be an intrinsic that is intended to be used as the [[Prototype]] value of an object.- Let proto be ?
Get (constructor,"prototype" ). - If proto
is not an Object , then- Let realm be ?
GetFunctionRealm (constructor). - Set proto to realm's intrinsic object named intrinsicDefaultProto.
- Let realm be ?
- Return proto.
If constructor does not supply a [[Prototype]] value, the default value that is used is obtained from the
10.1.15 RequireInternalSlot ( O, internalSlot )
The abstract operation RequireInternalSlot takes arguments O (an
- If O
is not an Object , throw aTypeError exception. - If O does not have an internalSlot internal slot, throw a
TypeError exception. - Return
unused .
10.2 ECMAScript Function Objects
ECMAScript
In addition to [[Extensible]] and [[Prototype]], ECMAScript
| Internal Slot | Type | Description |
|---|---|---|
| [[Environment]] |
an |
The |
| [[PrivateEnvironment]] |
a |
The |
| [[FormalParameters]] |
a |
The root parse node of the source text that defines the function's formal parameter list. |
| [[ECMAScriptCode]] |
a |
The root parse node of the source text that defines the function's body. |
| [[ConstructorKind]] |
|
Whether or not the function is a derived class |
| [[Realm]] |
a |
The |
| [[ScriptOrModule]] |
a |
The script or module in which the function was created. |
| [[ThisMode]] |
|
Defines how this references are interpreted within the formal parameters and code body of the function. this refers to the |
| [[Strict]] | a Boolean |
|
| [[HomeObject]] | an Object |
If the function uses super, this is the object whose [[GetPrototypeOf]] provides the object where super property lookups begin.
|
| [[SourceText]] | a sequence of Unicode code points |
The |
| [[Fields]] |
a |
If the function is a class, this is a list of |
| [[PrivateMethods]] |
a |
If the function is a class, this is a list representing the non-static private methods and accessors of the class. |
| [[ClassFieldInitializerName]] |
a String, a Symbol, a |
If the function is created as the initializer of a class field, the name to use for |
| [[IsClassConstructor]] | a Boolean |
Indicates whether the function is a class |
All ECMAScript
10.2.1 [[Call]] ( thisArgument, argumentsList )
The [[Call]] internal method of an ECMAScript
- Let callerContext be the
running execution context . - Let calleeContext be
PrepareForOrdinaryCall (F,undefined ). Assert : calleeContext is now therunning execution context .- If F.[[IsClassConstructor]] is
true , then- Let error be a newly created
TypeError object. - NOTE: error is created in calleeContext with F's associated
Realm Record . - Remove calleeContext from the
execution context stack and restore callerContext as therunning execution context . - Return
ThrowCompletion (error).
- Let error be a newly created
- Perform
OrdinaryCallBindThis (F, calleeContext, thisArgument). - Let result be
Completion (OrdinaryCallEvaluateBody (F, argumentsList)). - Remove calleeContext from the
execution context stack and restore callerContext as therunning execution context . - If result is a
return completion , return result.[[Value]]. Assert : result is athrow completion .- Return ? result.
When calleeContext is removed from the
10.2.1.1 PrepareForOrdinaryCall ( F, newTarget )
The abstract operation PrepareForOrdinaryCall takes arguments F (an ECMAScript
- Let callerContext be the
running execution context . - Let calleeContext be a new
ECMAScript code execution context . - Set the Function of calleeContext to F.
- Let calleeRealm be F.[[Realm]].
- Set the
Realm of calleeContext to calleeRealm. - Set the ScriptOrModule of calleeContext to F.[[ScriptOrModule]].
- Let localEnv be
NewFunctionEnvironment (F, newTarget). - Set the LexicalEnvironment of calleeContext to localEnv.
- Set the VariableEnvironment of calleeContext to localEnv.
- Set the PrivateEnvironment of calleeContext to F.[[PrivateEnvironment]].
- If callerContext is not already suspended, suspend callerContext.
- Push calleeContext onto the
execution context stack ; calleeContext is now therunning execution context . - NOTE: Any exception objects produced after this point are associated with calleeRealm.
- Return calleeContext.
10.2.1.2 OrdinaryCallBindThis ( F, calleeContext, thisArgument )
The abstract operation OrdinaryCallBindThis takes arguments F (an ECMAScript
- Let thisMode be F.[[ThisMode]].
- If thisMode is
lexical , returnunused . - Let calleeRealm be F.[[Realm]].
- Let localEnv be the LexicalEnvironment of calleeContext.
- If thisMode is
strict , then- Let thisValue be thisArgument.
- Else,
- If thisArgument is either
undefined ornull , then- Let globalEnv be calleeRealm.[[GlobalEnv]].
Assert : globalEnv is aGlobal Environment Record .- Let thisValue be globalEnv.[[GlobalThisValue]].
- Else,
- If thisArgument is either
Assert : localEnv is aFunction Environment Record .Assert : The next step never returns anabrupt completion because localEnv.[[ThisBindingStatus]] is notinitialized .- Perform !
BindThisValue (localEnv, thisValue). - Return
unused .
10.2.1.3 Runtime Semantics: EvaluateBody
The
- Return ?
EvaluateFunctionBody ofFunctionBody with arguments functionObject and argumentsList.
- Return ?
EvaluateConciseBody ofConciseBody with arguments functionObject and argumentsList.
- Return ?
EvaluateGeneratorBody ofGeneratorBody with arguments functionObject and argumentsList.
- Return ?
EvaluateAsyncGeneratorBody ofAsyncGeneratorBody with arguments functionObject and argumentsList.
- Return ?
EvaluateAsyncFunctionBody ofAsyncFunctionBody with arguments functionObject and argumentsList.
- Return ?
EvaluateAsyncConciseBody ofAsyncConciseBody with arguments functionObject and argumentsList.
Assert : argumentsList is empty.Assert : functionObject.[[ClassFieldInitializerName]] is notempty .- If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue , then- Let value be ?
NamedEvaluation ofInitializer with argument functionObject.[[ClassFieldInitializerName]].
- Let value be ?
- Else,
- Let rhs be ?
Evaluation ofAssignmentExpression . - Let value be ?
GetValue (rhs).
- Let rhs be ?
- Return
ReturnCompletion (value).
Even though field initializers constitute a function boundary, calling
Assert : argumentsList is empty.- Return ?
EvaluateClassStaticBlockBody ofClassStaticBlockBody with argument functionObject.
10.2.1.4 OrdinaryCallEvaluateBody ( F, argumentsList )
The abstract operation OrdinaryCallEvaluateBody takes arguments F (an ECMAScript
- Return ?
EvaluateBody of F.[[ECMAScriptCode]] with arguments F and argumentsList.
10.2.2 [[Construct]] ( argumentsList, newTarget )
The [[Construct]] internal method of an ECMAScript
- Let callerContext be the
running execution context . - Let kind be F.[[ConstructorKind]].
- If kind is
base , then- Let thisArgument be ?
OrdinaryCreateFromConstructor (newTarget,"%Object.prototype%" ).
- Let thisArgument be ?
- Let calleeContext be
PrepareForOrdinaryCall (F, newTarget). Assert : calleeContext is now therunning execution context .- If kind is
base , then- Perform
OrdinaryCallBindThis (F, calleeContext, thisArgument). - Let initializeResult be
Completion (InitializeInstanceElements (thisArgument, F)). - If initializeResult is an
abrupt completion , then- Remove calleeContext from the
execution context stack and restore callerContext as therunning execution context . - Return ? initializeResult.
- Remove calleeContext from the
- Perform
- Let constructorEnv be the LexicalEnvironment of calleeContext.
- Let result be
Completion (OrdinaryCallEvaluateBody (F, argumentsList)). - Remove calleeContext from the
execution context stack and restore callerContext as therunning execution context . - If result is a
throw completion , then- Return ? result.
Assert : result is areturn completion .- If result.[[Value]]
is an Object , return result.[[Value]]. - If kind is
base , return thisArgument. - If result.[[Value]] is not
undefined , throw aTypeError exception. - Let thisBinding be ? constructorEnv.GetThisBinding().
Assert : thisBindingis an Object .- Return thisBinding.
10.2.3 OrdinaryFunctionCreate ( functionPrototype, sourceText, ParameterList, Body, thisMode, env, privateEnv )
The abstract operation OrdinaryFunctionCreate takes arguments functionPrototype (an Object), sourceText (a sequence of Unicode code points), ParameterList (a
- Let internalSlotsList be the internal slots listed in
Table 30 . - Let F be
OrdinaryObjectCreate (functionPrototype, internalSlotsList). - Set F.[[Call]] to the definition specified in
10.2.1 . - Set F.[[SourceText]] to sourceText.
- Set F.[[FormalParameters]] to ParameterList.
- Set F.[[ECMAScriptCode]] to Body.
- Let Strict be
IsStrict (Body). - Set F.[[Strict]] to Strict.
- If thisMode is
lexical-this , set F.[[ThisMode]] tolexical . - Else if Strict is
true , set F.[[ThisMode]] tostrict . - Else, set F.[[ThisMode]] to
global . - Set F.[[IsClassConstructor]] to
false . - Set F.[[Environment]] to env.
- Set F.[[PrivateEnvironment]] to privateEnv.
- Set F.[[ScriptOrModule]] to
GetActiveScriptOrModule (). - Set F.[[Realm]] to
the current Realm Record . - Set F.[[HomeObject]] to
undefined . - Set F.[[Fields]] to a new empty
List . - Set F.[[PrivateMethods]] to a new empty
List . - Set F.[[ClassFieldInitializerName]] to
empty . - Let len be the
ExpectedArgumentCount of ParameterList. - Perform
SetFunctionLength (F, len). - Return F.
10.2.4 AddRestrictedFunctionProperties ( F, realm )
The abstract operation AddRestrictedFunctionProperties takes arguments F (a
Assert : realm.[[Intrinsics]].[[%ThrowTypeError% ]] exists and has been initialized.- Let thrower be realm.[[Intrinsics]].[[
%ThrowTypeError% ]]. - Perform !
DefinePropertyOrThrow (F,"caller" , PropertyDescriptor { [[Get]]: thrower, [[Set]]: thrower, [[Enumerable]]:false , [[Configurable]]:true }). - Perform !
DefinePropertyOrThrow (F,"arguments" , PropertyDescriptor { [[Get]]: thrower, [[Set]]: thrower, [[Enumerable]]:false , [[Configurable]]:true }). - Return
unused .
10.2.4.1 %ThrowTypeError% ( )
This function is the %ThrowTypeError% intrinsic object.
It is an anonymous built-in
It performs the following steps when called:
- Throw a
TypeError exception.
The value of the [[Extensible]] internal slot of this function is
The
The
10.2.5 MakeConstructor ( F [ , writablePrototype [ , prototype ] ] )
The abstract operation MakeConstructor takes argument F (an ECMAScript
- If F is an ECMAScript
function object , thenAssert :IsConstructor (F) isfalse .Assert : F is an extensible object that does not have a"prototype" own property.- Set F.[[Construct]] to the definition specified in
10.2.2 .
- Else,
- Set F.[[Construct]] to the definition specified in
10.3.2 .
- Set F.[[Construct]] to the definition specified in
- Set F.[[ConstructorKind]] to
base . - If writablePrototype is not present, set writablePrototype to
true . - If prototype is not present, then
- Set prototype to
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
DefinePropertyOrThrow (prototype,"constructor" , PropertyDescriptor { [[Value]]: F, [[Writable]]: writablePrototype, [[Enumerable]]:false , [[Configurable]]:true }).
- Set prototype to
- Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]: writablePrototype, [[Enumerable]]:false , [[Configurable]]:false }). - Return
unused .
10.2.6 MakeClassConstructor ( F )
The abstract operation MakeClassConstructor takes argument F (an ECMAScript
Assert : F.[[IsClassConstructor]] isfalse .- Set F.[[IsClassConstructor]] to
true . - Return
unused .
10.2.7 MakeMethod ( F, homeObject )
The abstract operation MakeMethod takes arguments F (an ECMAScript
Assert : homeObject is anordinary object .- Set F.[[HomeObject]] to homeObject.
- Return
unused .
10.2.8 DefineMethodProperty ( homeObject, key, closure, enumerable )
The abstract operation DefineMethodProperty takes arguments homeObject (an Object), key (a
Assert : homeObject is an ordinary, extensible object.- If key is a
Private Name , then- Return
PrivateElement { [[Key]]: key, [[Kind]]:method , [[Value]]: closure }.
- Return
- Else,
- Let desc be the PropertyDescriptor { [[Value]]: closure, [[Writable]]:
true , [[Enumerable]]: enumerable, [[Configurable]]:true }. - Perform ?
DefinePropertyOrThrow (homeObject, key, desc). - NOTE:
DefinePropertyOrThrow only returns anabrupt completion when attempting to define a class static method whose key is"prototype" . - Return
unused .
- Let desc be the PropertyDescriptor { [[Value]]: closure, [[Writable]]:
10.2.9 SetFunctionName ( F, name [ , prefix ] )
The abstract operation SetFunctionName takes arguments F (a
Assert : F is an extensible object that does not have a"name" own property.- If name
is a Symbol , then- Let description be name's [[Description]] value.
- If description is
undefined , set name to the empty String. - Else, set name to the
string-concatenation of"[" , description, and"]" .
- Else if name is a
Private Name , then- Set name to name.[[Description]].
- If F has an [[InitialName]] internal slot, then
- Set F.[[InitialName]] to name.
- If prefix is present, then
- Set name to the
string-concatenation of prefix, the code unit 0x0020 (SPACE), and name. - If F has an [[InitialName]] internal slot, then
- Optionally, set F.[[InitialName]] to name.
- Set name to the
- Perform !
DefinePropertyOrThrow (F,"name" , PropertyDescriptor { [[Value]]: name, [[Writable]]:false , [[Enumerable]]:false , [[Configurable]]:true }). - Return
unused .
10.2.10 SetFunctionLength ( F, length )
The abstract operation SetFunctionLength takes arguments F (a
Assert : F is an extensible object that does not have a"length" own property.- Perform !
DefinePropertyOrThrow (F,"length" , PropertyDescriptor { [[Value]]:𝔽 (length), [[Writable]]:false , [[Enumerable]]:false , [[Configurable]]:true }). - Return
unused .
10.2.11 FunctionDeclarationInstantiation ( func, argumentsList )
The abstract operation FunctionDeclarationInstantiation takes arguments func (an ECMAScript
When an
It performs the following steps when called:
- Let calleeContext be the
running execution context . - Let code be func.[[ECMAScriptCode]].
- Let strict be func.[[Strict]].
- Let formals be func.[[FormalParameters]].
- Let parameterNames be the
BoundNames of formals. - If parameterNames has any duplicate entries, let hasDuplicates be
true . Otherwise, let hasDuplicates befalse . - Let simpleParameterList be
IsSimpleParameterList of formals. - Let hasParameterExpressions be
ContainsExpression of formals. - Let varNames be the
VarDeclaredNames of code. - Let varDeclarations be the
VarScopedDeclarations of code. - Let lexicalNames be the
LexicallyDeclaredNames of code. - Let functionNames be a new empty
List . - Let functionsToInitialize be a new empty
List . - For each element d of varDeclarations, in reverse
List order, do- If d is neither a
VariableDeclaration nor aForBinding nor aBindingIdentifier , thenAssert : d is either aFunctionDeclaration , aGeneratorDeclaration , anAsyncFunctionDeclaration , or anAsyncGeneratorDeclaration .- Let fn be the sole element of the
BoundNames of d. - If functionNames does not contain fn, then
- Insert fn as the first element of functionNames.
- NOTE: If there are multiple function declarations for the same name, the last declaration is used.
- Insert d as the first element of functionsToInitialize.
- If d is neither a
- Let argumentsObjectNeeded be
true . - If func.[[ThisMode]] is
lexical , then- NOTE: Arrow functions never have an arguments object.
- Set argumentsObjectNeeded to
false .
- Else if parameterNames contains
"arguments" , then- Set argumentsObjectNeeded to
false .
- Set argumentsObjectNeeded to
- Else if hasParameterExpressions is
false , then- If functionNames contains
"arguments" or lexicalNames contains"arguments" , then- Set argumentsObjectNeeded to
false .
- Set argumentsObjectNeeded to
- If functionNames contains
- If strict is
true or hasParameterExpressions isfalse , then- NOTE: Only a single
Environment Record is needed for the parameters, since calls toevalinstrict mode code cannot create new bindings which are visible outside of theeval. - Let env be the LexicalEnvironment of calleeContext.
- NOTE: Only a single
- Else,
- NOTE: A separate
Environment Record is needed to ensure that bindings created bydirect eval calls in the formal parameter list are outside the environment where parameters are declared. - Let calleeEnv be the LexicalEnvironment of calleeContext.
- Let env be
NewDeclarativeEnvironment (calleeEnv). Assert : The VariableEnvironment of calleeContext and calleeEnv are the sameEnvironment Record .- Set the LexicalEnvironment of calleeContext to env.
- NOTE: A separate
- For each String paramName of parameterNames, do
- Let alreadyDeclared be ! env.HasBinding(paramName).
- NOTE:
Early errors ensure that duplicate parameter names can only occur innon-strict functions that do not have parameter default values or rest parameters. - If alreadyDeclared is
false , then- Perform ! env.CreateMutableBinding(paramName,
false ). - If hasDuplicates is
true , then- Perform ! env.InitializeBinding(paramName,
undefined ).
- Perform ! env.InitializeBinding(paramName,
- Perform ! env.CreateMutableBinding(paramName,
- If argumentsObjectNeeded is
true , then- If strict is
true or simpleParameterList isfalse , then- Let ao be
CreateUnmappedArgumentsObject (argumentsList).
- Let ao be
- Else,
- NOTE: A mapped argument object is only provided for
non-strict functions that don't have a rest parameter, any parameter default value initializers, or any destructured parameters. - Let ao be
CreateMappedArgumentsObject (func, formals, argumentsList, env).
- NOTE: A mapped argument object is only provided for
- If strict is
true , then- Perform ! env.CreateImmutableBinding(
"arguments" ,false ). - NOTE: In
strict mode code early errors prevent attempting to assign to this binding, so its mutability is not observable.
- Perform ! env.CreateImmutableBinding(
- Else,
- Perform ! env.CreateMutableBinding(
"arguments" ,false ).
- Perform ! env.CreateMutableBinding(
- Perform ! env.InitializeBinding(
"arguments" , ao). - Let parameterBindings be the
list-concatenation of parameterNames and «"arguments" ».
- If strict is
- Else,
- Let parameterBindings be parameterNames.
- Let iteratorRecord be
CreateListIteratorRecord (argumentsList). - If hasDuplicates is
true , then- Perform ?
IteratorBindingInitialization of formals with arguments iteratorRecord andundefined .
- Perform ?
- Else,
- Perform ?
IteratorBindingInitialization of formals with arguments iteratorRecord and env.
- Perform ?
- If hasParameterExpressions is
false , then- NOTE: Only a single
Environment Record is needed for the parameters and top-level vars. - Let instantiatedVarNames be a copy of the
List parameterBindings. - For each element n of varNames, do
- If instantiatedVarNames does not contain n, then
- Append n to instantiatedVarNames.
- Perform ! env.CreateMutableBinding(n,
false ). - Perform ! env.InitializeBinding(n,
undefined ).
- If instantiatedVarNames does not contain n, then
- Let varEnv be env.
- NOTE: Only a single
- Else,
- NOTE: A separate
Environment Record is needed to ensure that closures created by expressions in the formal parameter list do not have visibility of declarations in the function body. - Let varEnv be
NewDeclarativeEnvironment (env). - Set the VariableEnvironment of calleeContext to varEnv.
- Let instantiatedVarNames be a new empty
List . - For each element n of varNames, do
- If instantiatedVarNames does not contain n, then
- Append n to instantiatedVarNames.
- Perform ! varEnv.CreateMutableBinding(n,
false ). - If parameterBindings does not contain n, or if functionNames contains n, then
- Let initialValue be
undefined .
- Let initialValue be
- Else,
- Let initialValue be ! env.GetBindingValue(n,
false ).
- Let initialValue be ! env.GetBindingValue(n,
- Perform ! varEnv.InitializeBinding(n, initialValue).
- NOTE: A var with the same name as a formal parameter initially has the same value as the corresponding initialized parameter.
- If instantiatedVarNames does not contain n, then
- NOTE: A separate
- NOTE: Annex
B.3.2.1 adds additional steps at this point. - If strict is
false , then- Let lexEnv be
NewDeclarativeEnvironment (varEnv). - NOTE:
Non-strict functions use a separateEnvironment Record for top-level lexical declarations so that adirect eval can determine whether any var scoped declarations introduced by the eval code conflict with pre-existing top-level lexically scoped declarations. This is not needed forstrict functions because a strictdirect eval always places all declarations into a newEnvironment Record .
- Let lexEnv be
- Else,
- Let lexEnv be varEnv.
- Set the LexicalEnvironment of calleeContext to lexEnv.
- Let lexDeclarations be the
LexicallyScopedDeclarations of code. - For each element d of lexDeclarations, do
- NOTE: A lexically declared name cannot be the same as a function/generator declaration, formal parameter, or a var name. Lexically declared names are only instantiated here but not initialized.
- For each element dn of the
BoundNames of d, do- If
IsConstantDeclaration of d istrue , then- Perform ! lexEnv.CreateImmutableBinding(dn,
true ).
- Perform ! lexEnv.CreateImmutableBinding(dn,
- Else,
- Perform ! lexEnv.CreateMutableBinding(dn,
false ).
- Perform ! lexEnv.CreateMutableBinding(dn,
- If
- Let privateEnv be the PrivateEnvironment of calleeContext.
- For each
Parse Node f of functionsToInitialize, do- Let fn be the sole element of the
BoundNames of f. - Let fo be
InstantiateFunctionObject of f with arguments lexEnv and privateEnv. - Perform ! varEnv.SetMutableBinding(fn, fo,
false ).
- Let fn be the sole element of the
- Return
unused .
10.3 Built-in Function Objects
A built-in
In addition to the internal slots required of every
- [[Realm]], a
Realm Record that represents therealm in which the function was created. - [[InitialName]], a String that is the initial name of the function. It is used by
20.2.3.5 .
The initial value of a built-in
A built-in
A built-in
An implementation may provide additional built-in
10.3.1 [[Call]] ( thisArgument, argumentsList )
The [[Call]] internal method of a built-in
- Return ?
BuiltinCallOrConstruct (F, thisArgument, argumentsList,undefined ).
10.3.2 [[Construct]] ( argumentsList, newTarget )
The [[Construct]] internal method of a built-in
- Let result be ?
BuiltinCallOrConstruct (F,uninitialized , argumentsList, newTarget). Assert : resultis an Object .- Return result.
10.3.3 BuiltinCallOrConstruct ( F, thisArgument, argumentsList, newTarget )
The abstract operation BuiltinCallOrConstruct takes arguments F (a built-in
- Let callerContext be the
running execution context . - If callerContext is not already suspended, suspend callerContext.
- Let calleeContext be a new
execution context . - Set the Function of calleeContext to F.
- Let calleeRealm be F.[[Realm]].
- Set the
Realm of calleeContext to calleeRealm. - Set the ScriptOrModule of calleeContext to
null . - Perform any necessary
implementation-defined initialization of calleeContext. - Push calleeContext onto the
execution context stack ; calleeContext is now therunning execution context . - Let result be the
Completion Record that is the result of evaluating F in a manner that conforms to the specification of F. If thisArgument isuninitialized , thethis value is uninitialized; otherwise, thisArgument provides thethis value. argumentsList provides the named parameters. newTarget provides the NewTarget value. - NOTE: If F is defined in this document, “the specification of F” is the behaviour specified for it via algorithm steps or other means.
- Remove calleeContext from the
execution context stack and restore callerContext as therunning execution context . - Return ? result.
When calleeContext is removed from the
10.3.4 CreateBuiltinFunction ( behaviour, length, name, additionalInternalSlotsList [ , realm [ , prototype [ , prefix ] ] ] )
The abstract operation CreateBuiltinFunction takes arguments behaviour (an
- If realm is not present, set realm to
the current Realm Record . - If prototype is not present, set prototype to realm.[[Intrinsics]].[[
%Function.prototype% ]]. - Let internalSlotsList be a
List containing the names of all the internal slots that10.3 requires for the built-infunction object that is about to be created. - Append to internalSlotsList the elements of additionalInternalSlotsList.
- Let func be a new built-in
function object that, when called, performs the action described by behaviour using the provided arguments as the values of the corresponding parameters specified by behaviour. The newfunction object has internal slots whose names are the elements of internalSlotsList, and an [[InitialName]] internal slot. - Set func.[[Prototype]] to prototype.
- Set func.[[Extensible]] to
true . - Set func.[[Realm]] to realm.
- Set func.[[InitialName]] to
null . - Perform
SetFunctionLength (func, length). - If prefix is not present, then
- Perform
SetFunctionName (func, name).
- Perform
- Else,
- Perform
SetFunctionName (func, name, prefix).
- Perform
- Return func.
Each built-in function defined in this specification is created by calling the CreateBuiltinFunction abstract operation.
10.4 Built-in Exotic Object Internal Methods and Slots
This specification defines several kinds of built-in
10.4.1 Bound Function Exotic Objects
A
An object is a bound function exotic object if its [[Call]] and (if applicable) [[Construct]] internal methods use the following implementations, and its other essential internal methods use the definitions found in
| Internal Slot | Type | Description |
|---|---|---|
| [[BoundTargetFunction]] | a callable Object |
The wrapped |
| [[BoundThis]] |
an |
The value that is always passed as the |
| [[BoundArguments]] |
a |
A list of values whose elements are used as the first arguments to any call to the wrapped function. |
10.4.1.1 [[Call]] ( thisArgument, argumentsList )
The [[Call]] internal method of a
- Let target be F.[[BoundTargetFunction]].
- Let boundThis be F.[[BoundThis]].
- Let boundArgs be F.[[BoundArguments]].
- Let args be the
list-concatenation of boundArgs and argumentsList. - Return ?
Call (target, boundThis, args).
10.4.1.2 [[Construct]] ( argumentsList, newTarget )
The [[Construct]] internal method of a
- Let target be F.[[BoundTargetFunction]].
Assert :IsConstructor (target) istrue .- Let boundArgs be F.[[BoundArguments]].
- Let args be the
list-concatenation of boundArgs and argumentsList. - If
SameValue (F, newTarget) istrue , set newTarget to target. - Return ?
Construct (target, args, newTarget).
10.4.1.3 BoundFunctionCreate ( targetFunction, boundThis, boundArgs )
The abstract operation BoundFunctionCreate takes arguments targetFunction (a
- Let proto be ? targetFunction.[[GetPrototypeOf]]().
- Let internalSlotsList be the
list-concatenation of « [[Prototype]], [[Extensible]] » and the internal slots listed inTable 31 . - Let obj be
MakeBasicObject (internalSlotsList). - Set obj.[[Prototype]] to proto.
- Set obj.[[Call]] as described in
10.4.1.1 . - If
IsConstructor (targetFunction) istrue , then- Set obj.[[Construct]] as described in
10.4.1.2 .
- Set obj.[[Construct]] as described in
- Set obj.[[BoundTargetFunction]] to targetFunction.
- Set obj.[[BoundThis]] to boundThis.
- Set obj.[[BoundArguments]] to boundArgs.
- Return obj.
10.4.2 Array Exotic Objects
An Array is an
An object is an Array exotic object (or simply, an Array) if its [[DefineOwnProperty]] internal method uses the following implementation, and its other essential internal methods use the definitions found in
10.4.2.1 [[DefineOwnProperty]] ( P, Desc )
The [[DefineOwnProperty]] internal method of an
- If P is
"length" , then- Return ?
ArraySetLength (A, Desc).
- Return ?
- Else if P is an
array index , then- Let lengthDesc be
OrdinaryGetOwnProperty (A,"length" ). Assert :IsDataDescriptor (lengthDesc) istrue .Assert : lengthDesc.[[Configurable]] isfalse .- Let length be lengthDesc.[[Value]].
Assert : length is a non-negativeintegral Number .- Let index be !
ToUint32 (P). - If index ≥ length and lengthDesc.[[Writable]] is
false , returnfalse . - Let succeeded be !
OrdinaryDefineOwnProperty (A, P, Desc). - If succeeded is
false , returnfalse . - If index ≥ length, then
- Set lengthDesc.[[Value]] to index +
1 𝔽. - Set succeeded to !
OrdinaryDefineOwnProperty (A,"length" , lengthDesc). Assert : succeeded istrue .
- Set lengthDesc.[[Value]] to index +
- Return
true .
- Let lengthDesc be
- Return ?
OrdinaryDefineOwnProperty (A, P, Desc).
10.4.2.2 ArrayCreate ( length [ , proto ] )
The abstract operation ArrayCreate takes argument length (a non-negative
- If length > 232 - 1, throw a
RangeError exception. - If proto is not present, set proto to
%Array.prototype% . - Let A be
MakeBasicObject (« [[Prototype]], [[Extensible]] »). - Set A.[[Prototype]] to proto.
- Set A.[[DefineOwnProperty]] as specified in
10.4.2.1 . - Perform !
OrdinaryDefineOwnProperty (A,"length" , PropertyDescriptor { [[Value]]:𝔽 (length), [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return A.
10.4.2.3 ArraySpeciesCreate ( originalArray, length )
The abstract operation ArraySpeciesCreate takes arguments originalArray (an Object) and length (a non-negative
- Let isArray be ?
IsArray (originalArray). - If isArray is
false , return ?ArrayCreate (length). - Let C be ?
Get (originalArray,"constructor" ). - If
IsConstructor (C) istrue , then- Let thisRealm be
the current Realm Record . - Let realmC be ?
GetFunctionRealm (C). - If thisRealm and realmC are not the same
Realm Record , then
- Let thisRealm be
- If C
is an Object , then- Set C to ?
Get (C,%Symbol.species% ). - If C is
null , set C toundefined .
- Set C to ?
- If C is
undefined , return ?ArrayCreate (length). - If
IsConstructor (C) isfalse , throw aTypeError exception. - Return ?
Construct (C, «𝔽 (length) »).
If originalArray was created using the standard built-in Array Array.prototype methods that now are defined using ArraySpeciesCreate.
10.4.2.4 ArraySetLength ( A, Desc )
The abstract operation ArraySetLength takes arguments A (an Array) and Desc (a
- If Desc does not have a [[Value]] field, then
- Return !
OrdinaryDefineOwnProperty (A,"length" , Desc).
- Return !
- Let newLenDesc be a copy of Desc.
- Let newLen be ?
ToUint32 (Desc.[[Value]]). - Let numberLen be ?
ToNumber (Desc.[[Value]]). - If
SameValueZero (newLen, numberLen) isfalse , throw aRangeError exception. - Set newLenDesc.[[Value]] to newLen.
- Let oldLenDesc be
OrdinaryGetOwnProperty (A,"length" ). Assert :IsDataDescriptor (oldLenDesc) istrue .Assert : oldLenDesc.[[Configurable]] isfalse .- Let oldLen be oldLenDesc.[[Value]].
- If newLen ≥ oldLen, then
- Return !
OrdinaryDefineOwnProperty (A,"length" , newLenDesc).
- Return !
- If oldLenDesc.[[Writable]] is
false , returnfalse . - If newLenDesc does not have a [[Writable]] field or newLenDesc.[[Writable]] is
true , then- Let newWritable be
true .
- Let newWritable be
- Else,
- NOTE: Setting the [[Writable]] attribute to
false is deferred in case any elements cannot be deleted. - Let newWritable be
false . - Set newLenDesc.[[Writable]] to
true .
- NOTE: Setting the [[Writable]] attribute to
- Let succeeded be !
OrdinaryDefineOwnProperty (A,"length" , newLenDesc). - If succeeded is
false , returnfalse . - For each own
property key P of A such that P is anarray index and !ToUint32 (P) ≥ newLen, in descending numeric index order, do- Let deleteSucceeded be ! A.[[Delete]](P).
- If deleteSucceeded is
false , then- Set newLenDesc.[[Value]] to !
ToUint32 (P) +1 𝔽. - If newWritable is
false , set newLenDesc.[[Writable]] tofalse . - Perform !
OrdinaryDefineOwnProperty (A,"length" , newLenDesc). - Return
false .
- Set newLenDesc.[[Value]] to !
- If newWritable is
false , then- Set succeeded to !
OrdinaryDefineOwnProperty (A,"length" , PropertyDescriptor { [[Writable]]:false }). Assert : succeeded istrue .
- Set succeeded to !
- Return
true .
10.4.3 String Exotic Objects
A String object is an
An object is a String exotic object (or simply, a String object) if its [[GetOwnProperty]], [[DefineOwnProperty]], and [[OwnPropertyKeys]] internal methods use the following implementations, and its other essential internal methods use the definitions found in
10.4.3.1 [[GetOwnProperty]] ( P )
The [[GetOwnProperty]] internal method of a
- Let desc be
OrdinaryGetOwnProperty (S, P). - If desc is not
undefined , return desc. - Return
StringGetOwnProperty (S, P).
10.4.3.2 [[DefineOwnProperty]] ( P, Desc )
The [[DefineOwnProperty]] internal method of a
- Let stringDesc be
StringGetOwnProperty (S, P). - If stringDesc is not
undefined , then- Let extensible be S.[[Extensible]].
- Return
IsCompatiblePropertyDescriptor (extensible, Desc, stringDesc).
- Return !
OrdinaryDefineOwnProperty (S, P, Desc).
10.4.3.3 [[OwnPropertyKeys]] ( )
The [[OwnPropertyKeys]] internal method of a
- Let keys be a new empty
List . - Let str be O.[[StringData]].
Assert : stris a String .- Let len be the length of str.
- For each
integer i such that 0 ≤ i < len, in ascending order, do - For each own
property key P of O such that P is anarray index and !ToIntegerOrInfinity (P) ≥ len, in ascending numeric index order, do- Append P to keys.
- For each own
property key P of O such that Pis a String and P is not anarray index , in ascending chronological order of property creation, do- Append P to keys.
- For each own
property key P of O such that Pis a Symbol , in ascending chronological order of property creation, do- Append P to keys.
- Return keys.
10.4.3.4 StringCreate ( value, prototype )
The abstract operation StringCreate takes arguments value (a String) and prototype (an Object) and returns a
- Let S be
MakeBasicObject (« [[Prototype]], [[Extensible]], [[StringData]] »). - Set S.[[Prototype]] to prototype.
- Set S.[[StringData]] to value.
- Set S.[[GetOwnProperty]] as specified in
10.4.3.1 . - Set S.[[DefineOwnProperty]] as specified in
10.4.3.2 . - Set S.[[OwnPropertyKeys]] as specified in
10.4.3.3 . - Let length be the length of value.
- Perform !
DefinePropertyOrThrow (S,"length" , PropertyDescriptor { [[Value]]:𝔽 (length), [[Writable]]:false , [[Enumerable]]:false , [[Configurable]]:false }). - Return S.
10.4.3.5 StringGetOwnProperty ( S, P )
The abstract operation StringGetOwnProperty takes arguments S (an Object that has a [[StringData]] internal slot) and P (a
- If P
is not a String , returnundefined . - Let index be
CanonicalNumericIndexString (P). - If index is not an
integral Number , returnundefined . - If index is
-0 𝔽 or index <-0 𝔽, returnundefined . - Let str be S.[[StringData]].
Assert : stris a String .- Let len be the length of str.
- If
ℝ (index) ≥ len, returnundefined . - Let resultStr be the
substring of str fromℝ (index) toℝ (index) + 1. - Return the PropertyDescriptor { [[Value]]: resultStr, [[Writable]]:
false , [[Enumerable]]:true , [[Configurable]]:false }.
10.4.4 Arguments Exotic Objects
Most ECMAScript functions make an arguments object available to their code. Depending upon the characteristics of the function definition, its arguments object is either an
An object is an arguments exotic object if its internal methods use the following implementations, with the ones not specified here using those found in
While
Object.prototype.toString (
The
The ParameterMap object and its property values are used as a device for specifying the arguments object correspondence to argument bindings. The ParameterMap object and the objects that are the values of its properties are not directly observable from ECMAScript code. An ECMAScript implementation does not need to actually create or use such objects to implement the specified semantics.
Ordinary arguments objects define a non-configurable
ECMAScript implementations of
10.4.4.1 [[GetOwnProperty]] ( P )
The [[GetOwnProperty]] internal method of an
- Let desc be
OrdinaryGetOwnProperty (args, P). - If desc is
undefined , returnundefined . - Let map be args.[[ParameterMap]].
- Let isMapped be !
HasOwnProperty (map, P). - If isMapped is
true , then- Set desc.[[Value]] to !
Get (map, P).
- Set desc.[[Value]] to !
- Return desc.
10.4.4.2 [[DefineOwnProperty]] ( P, Desc )
The [[DefineOwnProperty]] internal method of an
- Let map be args.[[ParameterMap]].
- Let isMapped be !
HasOwnProperty (map, P). - Let newArgDesc be Desc.
- If isMapped is
true andIsDataDescriptor (Desc) istrue , then- If Desc does not have a [[Value]] field, Desc has a [[Writable]] field, and Desc.[[Writable]] is
false , then- Set newArgDesc to a copy of Desc.
- Set newArgDesc.[[Value]] to !
Get (map, P).
- If Desc does not have a [[Value]] field, Desc has a [[Writable]] field, and Desc.[[Writable]] is
- Let allowed be !
OrdinaryDefineOwnProperty (args, P, newArgDesc). - If allowed is
false , returnfalse . - If isMapped is
true , then- If
IsAccessorDescriptor (Desc) istrue , then- Perform ! map.[[Delete]](P).
- Else,
- If
- Return
true .
10.4.4.3 [[Get]] ( P, Receiver )
The [[Get]] internal method of an
- Let map be args.[[ParameterMap]].
- Let isMapped be !
HasOwnProperty (map, P). - If isMapped is
false , then- Return ?
OrdinaryGet (args, P, Receiver).
- Return ?
- Else,
10.4.4.4 [[Set]] ( P, V, Receiver )
The [[Set]] internal method of an
- If
SameValue (args, Receiver) isfalse , then- Let isMapped be
false .
- Let isMapped be
- Else,
- Let map be args.[[ParameterMap]].
- Let isMapped be !
HasOwnProperty (map, P).
- If isMapped is
true , then - Return ?
OrdinarySet (args, P, V, Receiver).
10.4.4.5 [[Delete]] ( P )
The [[Delete]] internal method of an
- Let map be args.[[ParameterMap]].
- Let isMapped be !
HasOwnProperty (map, P). - Let result be ?
OrdinaryDelete (args, P). - If result is
true and isMapped istrue , then- Perform ! map.[[Delete]](P).
- Return result.
10.4.4.6 CreateUnmappedArgumentsObject ( argumentsList )
The abstract operation CreateUnmappedArgumentsObject takes argument argumentsList (a
- Let len be the number of elements in argumentsList.
- Let obj be
OrdinaryObjectCreate (%Object.prototype% , « [[ParameterMap]] »). - Set obj.[[ParameterMap]] to
undefined . - Perform !
DefinePropertyOrThrow (obj,"length" , PropertyDescriptor { [[Value]]:𝔽 (len), [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:true }). - Let index be 0.
- Repeat, while index < len,
- Let val be argumentsList[index].
- Perform !
CreateDataPropertyOrThrow (obj, !ToString (𝔽 (index)), val). - Set index to index + 1.
- Perform !
DefinePropertyOrThrow (obj,%Symbol.iterator% , PropertyDescriptor { [[Value]]: %Array.prototype.values%, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:true }). - Perform !
DefinePropertyOrThrow (obj,"callee" , PropertyDescriptor { [[Get]]:%ThrowTypeError% , [[Set]]:%ThrowTypeError% , [[Enumerable]]:false , [[Configurable]]:false }). - Return obj.
10.4.4.7 CreateMappedArgumentsObject ( func, formals, argumentsList, env )
The abstract operation CreateMappedArgumentsObject takes arguments func (an Object), formals (a
Assert : formals does not contain a rest parameter, any binding patterns, or any initializers. It may contain duplicate identifiers.- Let len be the number of elements in argumentsList.
- Let obj be
MakeBasicObject (« [[Prototype]], [[Extensible]], [[ParameterMap]] »). - Set obj.[[GetOwnProperty]] as specified in
10.4.4.1 . - Set obj.[[DefineOwnProperty]] as specified in
10.4.4.2 . - Set obj.[[Get]] as specified in
10.4.4.3 . - Set obj.[[Set]] as specified in
10.4.4.4 . - Set obj.[[Delete]] as specified in
10.4.4.5 . - Set obj.[[Prototype]] to
%Object.prototype% . - Let map be
OrdinaryObjectCreate (null ). - Set obj.[[ParameterMap]] to map.
- Let parameterNames be the
BoundNames of formals. - Let numberOfParameters be the number of elements in parameterNames.
- Let index be 0.
- Repeat, while index < len,
- Let val be argumentsList[index].
- Perform !
CreateDataPropertyOrThrow (obj, !ToString (𝔽 (index)), val). - Set index to index + 1.
- Perform !
DefinePropertyOrThrow (obj,"length" , PropertyDescriptor { [[Value]]:𝔽 (len), [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:true }). - Let mappedNames be a new empty
List . - Set index to numberOfParameters - 1.
- Repeat, while index ≥ 0,
- Let name be parameterNames[index].
- If mappedNames does not contain name, then
- Append name to mappedNames.
- If index < len, then
- Let g be
MakeArgGetter (name, env). - Let p be
MakeArgSetter (name, env). - Perform ! map.[[DefineOwnProperty]](!
ToString (𝔽 (index)), PropertyDescriptor { [[Set]]: p, [[Get]]: g, [[Enumerable]]:false , [[Configurable]]:true }).
- Let g be
- Set index to index - 1.
- Perform !
DefinePropertyOrThrow (obj,%Symbol.iterator% , PropertyDescriptor { [[Value]]: %Array.prototype.values%, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:true }). - Perform !
DefinePropertyOrThrow (obj,"callee" , PropertyDescriptor { [[Value]]: func, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:true }). - Return obj.
10.4.4.7.1 MakeArgGetter ( name, env )
The abstract operation MakeArgGetter takes arguments name (a String) and env (an
- Let getterClosure be a new
Abstract Closure with no parameters that captures name and env and performs the following steps when called:- Return env.GetBindingValue(name,
false ).
- Return env.GetBindingValue(name,
- Let getter be
CreateBuiltinFunction (getterClosure, 0,"" , « »). - NOTE: getter is never directly accessible to ECMAScript code.
- Return getter.
10.4.4.7.2 MakeArgSetter ( name, env )
The abstract operation MakeArgSetter takes arguments name (a String) and env (an
- Let setterClosure be a new
Abstract Closure with parameters (value) that captures name and env and performs the following steps when called:- Return ! env.SetMutableBinding(name, value,
false ).
- Return ! env.SetMutableBinding(name, value,
- Let setter be
CreateBuiltinFunction (setterClosure, 1,"" , « »). - NOTE: setter is never directly accessible to ECMAScript code.
- Return setter.
10.4.5 TypedArray Exotic Objects
A
An object is a TypedArray if its [[PreventExtensions]], [[GetOwnProperty]], [[HasProperty]], [[DefineOwnProperty]], [[Get]], [[Set]], [[Delete]], and [[OwnPropertyKeys]], internal methods use the definitions in this section, and its other essential internal methods use the definitions found in
10.4.5.1 [[PreventExtensions]] ( )
The [[PreventExtensions]] internal method of a
- NOTE: The extensibility-related invariants specified in
6.1.7.3 do not allow this method to returntrue when O can gain (or lose and then regain) properties, which might occur for properties withinteger index names when its underlying buffer is resized. - If
IsTypedArrayFixedLength (O) isfalse , returnfalse . - Return
OrdinaryPreventExtensions (O).
10.4.5.2 [[GetOwnProperty]] ( P )
The [[GetOwnProperty]] internal method of a
- If P
is a String , then- Let numericIndex be
CanonicalNumericIndexString (P). - If numericIndex is not
undefined , then- Let value be
TypedArrayGetElement (O, numericIndex). - If value is
undefined , returnundefined . - Return the PropertyDescriptor { [[Value]]: value, [[Writable]]:
true , [[Enumerable]]:true , [[Configurable]]:true }.
- Let value be
- Let numericIndex be
- Return
OrdinaryGetOwnProperty (O, P).
10.4.5.3 [[HasProperty]] ( P )
The [[HasProperty]] internal method of a
- If P
is a String , then- Let numericIndex be
CanonicalNumericIndexString (P). - If numericIndex is not
undefined , returnIsValidIntegerIndex (O, numericIndex).
- Let numericIndex be
- Return ?
OrdinaryHasProperty (O, P).
10.4.5.4 [[DefineOwnProperty]] ( P, Desc )
The [[DefineOwnProperty]] internal method of a
- If P
is a String , then- Let numericIndex be
CanonicalNumericIndexString (P). - If numericIndex is not
undefined , then- If
IsValidIntegerIndex (O, numericIndex) isfalse , returnfalse . - If Desc has a [[Configurable]] field and Desc.[[Configurable]] is
false , returnfalse . - If Desc has an [[Enumerable]] field and Desc.[[Enumerable]] is
false , returnfalse . - If
IsAccessorDescriptor (Desc) istrue , returnfalse . - If Desc has a [[Writable]] field and Desc.[[Writable]] is
false , returnfalse . - If Desc has a [[Value]] field, perform ?
TypedArraySetElement (O, numericIndex, Desc.[[Value]]). - Return
true .
- If
- Let numericIndex be
- Return !
OrdinaryDefineOwnProperty (O, P, Desc).
10.4.5.5 [[Get]] ( P, Receiver )
The [[Get]] internal method of a
- If P
is a String , then- Let numericIndex be
CanonicalNumericIndexString (P). - If numericIndex is not
undefined , then- Return
TypedArrayGetElement (O, numericIndex).
- Return
- Let numericIndex be
- Return ?
OrdinaryGet (O, P, Receiver).
10.4.5.6 [[Set]] ( P, V, Receiver )
The [[Set]] internal method of a
- If P
is a String , then- Let numericIndex be
CanonicalNumericIndexString (P). - If numericIndex is not
undefined , then- If
SameValue (O, Receiver) istrue , then- Perform ?
TypedArraySetElement (O, numericIndex, V). - Return
true .
- Perform ?
- If
IsValidIntegerIndex (O, numericIndex) isfalse , returntrue .
- If
- Let numericIndex be
- Return ?
OrdinarySet (O, P, V, Receiver).
10.4.5.7 [[Delete]] ( P )
The [[Delete]] internal method of a
- If P
is a String , then- Let numericIndex be
CanonicalNumericIndexString (P). - If numericIndex is not
undefined , then- If
IsValidIntegerIndex (O, numericIndex) isfalse , returntrue ; else returnfalse .
- If
- Let numericIndex be
- Return !
OrdinaryDelete (O, P).
10.4.5.8 [[OwnPropertyKeys]] ( )
The [[OwnPropertyKeys]] internal method of a
- Let taRecord be
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - Let keys be a new empty
List . - If
IsTypedArrayOutOfBounds (taRecord) isfalse , then- Let length be
TypedArrayLength (taRecord). - For each
integer i such that 0 ≤ i < length, in ascending order, do
- Let length be
- For each own
property key P of O such that Pis a String and P is not aninteger index , in ascending chronological order of property creation, do- Append P to keys.
- For each own
property key P of O such that Pis a Symbol , in ascending chronological order of property creation, do- Append P to keys.
- Return keys.
10.4.5.9 TypedArray With Buffer Witness Records
An TypedArray With Buffer Witness Record is a
TypedArray With Buffer Witness Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Object]] |
a |
The |
| [[CachedBufferByteLength]] |
a non-negative |
The byte length of the object's [[ViewedArrayBuffer]] when the |
10.4.5.10 MakeTypedArrayWithBufferWitnessRecord ( obj, order )
The abstract operation MakeTypedArrayWithBufferWitnessRecord takes arguments obj (a
- Let buffer be obj.[[ViewedArrayBuffer]].
- If
IsDetachedBuffer (buffer) istrue , then- Let byteLength be
detached .
- Let byteLength be
- Else,
- Let byteLength be
ArrayBufferByteLength (buffer, order).
- Let byteLength be
- Return the
TypedArray With Buffer Witness Record { [[Object]]: obj, [[CachedBufferByteLength]]: byteLength }.
10.4.5.11 TypedArrayCreate ( prototype )
The abstract operation TypedArrayCreate takes argument prototype (an Object) and returns a
- Let internalSlotsList be « [[Prototype]], [[Extensible]], [[ViewedArrayBuffer]], [[TypedArrayName]], [[ContentType]], [[ByteLength]], [[ByteOffset]], [[ArrayLength]] ».
- Let A be
MakeBasicObject (internalSlotsList). - Set A.[[PreventExtensions]] as specified in
10.4.5.1 . - Set A.[[GetOwnProperty]] as specified in
10.4.5.2 . - Set A.[[HasProperty]] as specified in
10.4.5.3 . - Set A.[[DefineOwnProperty]] as specified in
10.4.5.4 . - Set A.[[Get]] as specified in
10.4.5.5 . - Set A.[[Set]] as specified in
10.4.5.6 . - Set A.[[Delete]] as specified in
10.4.5.7 . - Set A.[[OwnPropertyKeys]] as specified in
10.4.5.8 . - Set A.[[Prototype]] to prototype.
- Return A.
10.4.5.12 TypedArrayByteLength ( taRecord )
The abstract operation TypedArrayByteLength takes argument taRecord (a
- If
IsTypedArrayOutOfBounds (taRecord) istrue , return 0. - Let length be
TypedArrayLength (taRecord). - If length = 0, return 0.
- Let O be taRecord.[[Object]].
- If O.[[ByteLength]] is not
auto , return O.[[ByteLength]]. - Let elementSize be
TypedArrayElementSize (O). - Return length × elementSize.
10.4.5.13 TypedArrayLength ( taRecord )
The abstract operation TypedArrayLength takes argument taRecord (a
Assert :IsTypedArrayOutOfBounds (taRecord) isfalse .- Let O be taRecord.[[Object]].
- If O.[[ArrayLength]] is not
auto , return O.[[ArrayLength]]. Assert :IsFixedLengthArrayBuffer (O.[[ViewedArrayBuffer]]) isfalse .- Let byteOffset be O.[[ByteOffset]].
- Let elementSize be
TypedArrayElementSize (O). - Let byteLength be taRecord.[[CachedBufferByteLength]].
Assert : byteLength is notdetached .- Return
floor ((byteLength - byteOffset) / elementSize).
10.4.5.14 IsTypedArrayOutOfBounds ( taRecord )
The abstract operation IsTypedArrayOutOfBounds takes argument taRecord (a
- Let O be taRecord.[[Object]].
- Let bufferByteLength be taRecord.[[CachedBufferByteLength]].
Assert :IsDetachedBuffer (O.[[ViewedArrayBuffer]]) istrue if and only if bufferByteLength isdetached .- If bufferByteLength is
detached , returntrue . - Let byteOffsetStart be O.[[ByteOffset]].
- If O.[[ArrayLength]] is
auto , then- Let byteOffsetEnd be bufferByteLength.
- Else,
- Let elementSize be
TypedArrayElementSize (O). - Let byteOffsetEnd be byteOffsetStart + O.[[ArrayLength]] × elementSize.
- Let elementSize be
- If byteOffsetStart > bufferByteLength or byteOffsetEnd > bufferByteLength, return
true . - NOTE: 0-length
TypedArrays are not considered out-of-bounds. - Return
false .
10.4.5.15 IsTypedArrayFixedLength ( O )
The abstract operation IsTypedArrayFixedLength takes argument O (a
- If O.[[ArrayLength]] is
auto , returnfalse . - Let buffer be O.[[ViewedArrayBuffer]].
- If
IsFixedLengthArrayBuffer (buffer) isfalse andIsSharedArrayBuffer (buffer) isfalse , returnfalse . - Return
true .
10.4.5.16 IsValidIntegerIndex ( O, index )
The abstract operation IsValidIntegerIndex takes arguments O (a
- If
IsDetachedBuffer (O.[[ViewedArrayBuffer]]) istrue , returnfalse . - If index is not an
integral Number , returnfalse . - If index is
-0 𝔽 or index <-0 𝔽, returnfalse . - Let taRecord be
MakeTypedArrayWithBufferWitnessRecord (O,unordered ). - NOTE: Bounds checking is not a synchronizing operation when O's backing buffer is a
growable SharedArrayBuffer . - If
IsTypedArrayOutOfBounds (taRecord) istrue , returnfalse . - Let length be
TypedArrayLength (taRecord). - If
ℝ (index) ≥ length, returnfalse . - Return
true .
10.4.5.17 TypedArrayGetElement ( O, index )
The abstract operation TypedArrayGetElement takes arguments O (a
- If
IsValidIntegerIndex (O, index) isfalse , returnundefined . - Let offset be O.[[ByteOffset]].
- Let elementSize be
TypedArrayElementSize (O). - Let byteIndexInBuffer be (
ℝ (index) × elementSize) + offset. - Let elementType be
TypedArrayElementType (O). - Return
GetValueFromBuffer (O.[[ViewedArrayBuffer]], byteIndexInBuffer, elementType,true ,unordered ).
10.4.5.18 TypedArraySetElement ( O, index, value )
The abstract operation TypedArraySetElement takes arguments O (a
- If O.[[ContentType]] is
bigint , let numValue be ?ToBigInt (value). - Otherwise, let numValue be ?
ToNumber (value). - If
IsValidIntegerIndex (O, index) istrue , then- Let offset be O.[[ByteOffset]].
- Let elementSize be
TypedArrayElementSize (O). - Let byteIndexInBuffer be (
ℝ (index) × elementSize) + offset. - Let elementType be
TypedArrayElementType (O). - Perform
SetValueInBuffer (O.[[ViewedArrayBuffer]], byteIndexInBuffer, elementType, numValue,true ,unordered ).
- Return
unused .
This operation always appears to succeed, but it has no effect when attempting to write past the end of a
10.4.5.19 IsArrayBufferViewOutOfBounds ( O )
The abstract operation IsArrayBufferViewOutOfBounds takes argument O (a
- If O has a [[DataView]] internal slot, then
- Let viewRecord be
MakeDataViewWithBufferWitnessRecord (O,seq-cst ). - Return
IsViewOutOfBounds (viewRecord).
- Let viewRecord be
- Let taRecord be
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - Return
IsTypedArrayOutOfBounds (taRecord).
10.4.6 Module Namespace Exotic Objects
A export * export items. Each String-valued own
An object is a module namespace exotic object if its [[GetPrototypeOf]], [[SetPrototypeOf]], [[IsExtensible]], [[PreventExtensions]], [[GetOwnProperty]], [[DefineOwnProperty]], [[HasProperty]], [[Get]], [[Set]], [[Delete]], and [[OwnPropertyKeys]] internal methods use the definitions in this section, and its other essential internal methods use the definitions found in
| Internal Slot | Type | Description |
|---|---|---|
| [[Module]] |
a |
The |
| [[Exports]] |
a |
A |
10.4.6.1 [[GetPrototypeOf]] ( )
The [[GetPrototypeOf]] internal method of a
- Return
null .
10.4.6.2 [[SetPrototypeOf]] ( V )
The [[SetPrototypeOf]] internal method of a
- Return !
SetImmutablePrototype (O, V).
10.4.6.3 [[IsExtensible]] ( )
The [[IsExtensible]] internal method of a
- Return
false .
10.4.6.4 [[PreventExtensions]] ( )
The [[PreventExtensions]] internal method of a
- Return
true .
10.4.6.5 [[GetOwnProperty]] ( P )
The [[GetOwnProperty]] internal method of a
- If P
is a Symbol , returnOrdinaryGetOwnProperty (O, P). - Let exports be O.[[Exports]].
- If exports does not contain P, return
undefined . - Let value be ? O.[[Get]](P, O).
- Return PropertyDescriptor { [[Value]]: value, [[Writable]]:
true , [[Enumerable]]:true , [[Configurable]]:false }.
10.4.6.6 [[DefineOwnProperty]] ( P, Desc )
The [[DefineOwnProperty]] internal method of a
- If P
is a Symbol , return !OrdinaryDefineOwnProperty (O, P, Desc). - Let current be ? O.[[GetOwnProperty]](P).
- If current is
undefined , returnfalse . - If Desc has a [[Configurable]] field and Desc.[[Configurable]] is
true , returnfalse . - If Desc has an [[Enumerable]] field and Desc.[[Enumerable]] is
false , returnfalse . - If
IsAccessorDescriptor (Desc) istrue , returnfalse . - If Desc has a [[Writable]] field and Desc.[[Writable]] is
false , returnfalse . - If Desc has a [[Value]] field, return
SameValue (Desc.[[Value]], current.[[Value]]). - Return
true .
10.4.6.7 [[HasProperty]] ( P )
The [[HasProperty]] internal method of a
- If P
is a Symbol , return !OrdinaryHasProperty (O, P). - Let exports be O.[[Exports]].
- If exports contains P, return
true . - Return
false .
10.4.6.8 [[Get]] ( P, Receiver )
The [[Get]] internal method of a
- If P
is a Symbol , then- Return !
OrdinaryGet (O, P, Receiver).
- Return !
- Let exports be O.[[Exports]].
- If exports does not contain P, return
undefined . - Let m be O.[[Module]].
- Let binding be m.ResolveExport(P).
Assert : binding is aResolvedBinding Record .- Let targetModule be binding.[[Module]].
Assert : targetModule is notundefined .- If binding.[[BindingName]] is
namespace , then- Return
GetModuleNamespace (targetModule).
- Return
- Let targetEnv be targetModule.[[Environment]].
- If targetEnv is
empty , throw aReferenceError exception. - Return ? targetEnv.GetBindingValue(binding.[[BindingName]],
true ).
ResolveExport is side-effect free. Each time this operation is called with a specific exportName, resolveSet pair as arguments it must return the same result. An implementation might choose to pre-compute or cache the ResolveExport results for the [[Exports]] of each
10.4.6.9 [[Set]] ( P, V, Receiver )
The [[Set]] internal method of a
- Return
false .
10.4.6.10 [[Delete]] ( P )
The [[Delete]] internal method of a
- If P
is a Symbol , then- Return !
OrdinaryDelete (O, P).
- Return !
- Let exports be O.[[Exports]].
- If exports contains P, return
false . - Return
true .
10.4.6.11 [[OwnPropertyKeys]] ( )
The [[OwnPropertyKeys]] internal method of a
- Let exports be O.[[Exports]].
- Let symbolKeys be
OrdinaryOwnPropertyKeys (O). - Return the
list-concatenation of exports and symbolKeys.
10.4.6.12 ModuleNamespaceCreate ( module, exports )
The abstract operation ModuleNamespaceCreate takes arguments module (a
Assert : module.[[Namespace]] isempty .- Let internalSlotsList be the internal slots listed in
Table 33 . - Let M be
MakeBasicObject (internalSlotsList). - Set M's essential internal methods to the definitions specified in
10.4.6 . - Set M.[[Module]] to module.
- Let sortedExports be a
List whose elements are the elements of exports, sorted according tolexicographic code unit order . - Set M.[[Exports]] to sortedExports.
- Create own properties of M corresponding to the definitions in
28.3 . - Set module.[[Namespace]] to M.
- Return M.
10.4.7 Immutable Prototype Exotic Objects
An
An object is an immutable prototype exotic object if its [[SetPrototypeOf]] internal method uses the following implementation. (Its other essential internal methods may use any implementation, depending on the specific
Unlike other
10.4.7.1 [[SetPrototypeOf]] ( V )
The [[SetPrototypeOf]] internal method of an
- Return ?
SetImmutablePrototype (O, V).
10.4.7.2 SetImmutablePrototype ( O, V )
The abstract operation SetImmutablePrototype takes arguments O (an Object) and V (an Object or
- Let current be ? O.[[GetPrototypeOf]]().
- If
SameValue (V, current) istrue , returntrue . - Return
false .
10.5 Proxy Object Internal Methods and Internal Slots
A Proxy object is an
An object is a Proxy exotic object if its essential internal methods (including [[Call]] and [[Construct]], if applicable) use the definitions in this section. These internal methods are installed in
| Internal Method | Handler Method |
|---|---|
| [[GetPrototypeOf]] |
getPrototypeOf
|
| [[SetPrototypeOf]] |
setPrototypeOf
|
| [[IsExtensible]] |
isExtensible
|
| [[PreventExtensions]] |
preventExtensions
|
| [[GetOwnProperty]] |
getOwnPropertyDescriptor
|
| [[DefineOwnProperty]] |
defineProperty
|
| [[HasProperty]] |
has
|
| [[Get]] |
get
|
| [[Set]] |
set
|
| [[Delete]] |
deleteProperty
|
| [[OwnPropertyKeys]] |
ownKeys
|
| [[Call]] |
apply
|
| [[Construct]] |
construct
|
When a handler method is called to provide the implementation of a Proxy object internal method, the handler method is passed the proxy's target object as a parameter. A proxy's handler object does not necessarily have a method corresponding to every essential internal method. Invoking an internal method on the proxy results in the invocation of the corresponding internal method on the proxy's target object if the handler object does not have a method corresponding to the internal trap.
The [[ProxyHandler]] and [[ProxyTarget]] internal slots of a Proxy object are always initialized when the object is created and typically may not be modified. Some Proxy objects are created in a manner that permits them to be subsequently revoked. When a proxy is revoked, its [[ProxyHandler]] and [[ProxyTarget]] internal slots are set to
Because Proxy objects permit the implementation of internal methods to be provided by arbitrary ECMAScript code, it is possible to define a Proxy object whose handler methods violates the invariants defined in
In the following algorithm descriptions, assume O is an ECMAScript Proxy object, P is a
10.5.1 [[GetPrototypeOf]] ( )
The [[GetPrototypeOf]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Let target be O.[[ProxyTarget]].
- Let handler be O.[[ProxyHandler]].
Assert : handleris an Object .- Let trap be ?
GetMethod (handler,"getPrototypeOf" ). - If trap is
undefined , then- Return ? target.[[GetPrototypeOf]]().
- Let handlerProto be ?
Call (trap, handler, « target »). - If handlerProto
is not an Object and handlerProto is notnull , throw aTypeError exception. - Let extensibleTarget be ?
IsExtensible (target). - If extensibleTarget is
true , return handlerProto. - Let targetProto be ? target.[[GetPrototypeOf]]().
- If
SameValue (handlerProto, targetProto) isfalse , throw aTypeError exception. - Return handlerProto.
[[GetPrototypeOf]] for Proxy objects enforces the following invariants:
-
The result of [[GetPrototypeOf]] must be either an Object or
null . - If the target object is not extensible, [[GetPrototypeOf]] applied to the Proxy object must return the same value as [[GetPrototypeOf]] applied to the Proxy object's target object.
10.5.2 [[SetPrototypeOf]] ( V )
The [[SetPrototypeOf]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Let target be O.[[ProxyTarget]].
- Let handler be O.[[ProxyHandler]].
Assert : handleris an Object .- Let trap be ?
GetMethod (handler,"setPrototypeOf" ). - If trap is
undefined , then- Return ? target.[[SetPrototypeOf]](V).
- Let booleanTrapResult be
ToBoolean (?Call (trap, handler, « target, V »)). - If booleanTrapResult is
false , returnfalse . - Let extensibleTarget be ?
IsExtensible (target). - If extensibleTarget is
true , returntrue . - Let targetProto be ? target.[[GetPrototypeOf]]().
- If
SameValue (V, targetProto) isfalse , throw aTypeError exception. - Return
true .
[[SetPrototypeOf]] for Proxy objects enforces the following invariants:
-
The result of [[SetPrototypeOf]]
is a Boolean value. - If the target object is not extensible, the argument value must be the same as the result of [[GetPrototypeOf]] applied to target object.
10.5.3 [[IsExtensible]] ( )
The [[IsExtensible]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Let target be O.[[ProxyTarget]].
- Let handler be O.[[ProxyHandler]].
Assert : handleris an Object .- Let trap be ?
GetMethod (handler,"isExtensible" ). - If trap is
undefined , then- Return ?
IsExtensible (target).
- Return ?
- Let booleanTrapResult be
ToBoolean (?Call (trap, handler, « target »)). - Let targetResult be ?
IsExtensible (target). - If booleanTrapResult is not targetResult, throw a
TypeError exception. - Return booleanTrapResult.
[[IsExtensible]] for Proxy objects enforces the following invariants:
-
The result of [[IsExtensible]]
is a Boolean value. - [[IsExtensible]] applied to the Proxy object must return the same value as [[IsExtensible]] applied to the Proxy object's target object with the same argument.
10.5.4 [[PreventExtensions]] ( )
The [[PreventExtensions]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Let target be O.[[ProxyTarget]].
- Let handler be O.[[ProxyHandler]].
Assert : handleris an Object .- Let trap be ?
GetMethod (handler,"preventExtensions" ). - If trap is
undefined , then- Return ? target.[[PreventExtensions]]().
- Let booleanTrapResult be
ToBoolean (?Call (trap, handler, « target »)). - If booleanTrapResult is
true , then- Let extensibleTarget be ?
IsExtensible (target). - If extensibleTarget is
true , throw aTypeError exception.
- Let extensibleTarget be ?
- Return booleanTrapResult.
[[PreventExtensions]] for Proxy objects enforces the following invariants:
-
The result of [[PreventExtensions]]
is a Boolean value. -
[[PreventExtensions]] applied to the Proxy object only returns
true if [[IsExtensible]] applied to the Proxy object's target object isfalse .
10.5.5 [[GetOwnProperty]] ( P )
The [[GetOwnProperty]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Let target be O.[[ProxyTarget]].
- Let handler be O.[[ProxyHandler]].
Assert : handleris an Object .- Let trap be ?
GetMethod (handler,"getOwnPropertyDescriptor" ). - If trap is
undefined , then- Return ? target.[[GetOwnProperty]](P).
- Let trapResultObj be ?
Call (trap, handler, « target, P »). - If trapResultObj
is not an Object and trapResultObj is notundefined , throw aTypeError exception. - Let targetDesc be ? target.[[GetOwnProperty]](P).
- If trapResultObj is
undefined , then- If targetDesc is
undefined , returnundefined . - If targetDesc.[[Configurable]] is
false , throw aTypeError exception. - Let extensibleTarget be ?
IsExtensible (target). - If extensibleTarget is
false , throw aTypeError exception. - Return
undefined .
- If targetDesc is
- Let extensibleTarget be ?
IsExtensible (target). - Let resultDesc be ?
ToPropertyDescriptor (trapResultObj). - Perform
CompletePropertyDescriptor (resultDesc). - Let valid be
IsCompatiblePropertyDescriptor (extensibleTarget, resultDesc, targetDesc). - If valid is
false , throw aTypeError exception. - If resultDesc.[[Configurable]] is
false , then- If targetDesc is
undefined or targetDesc.[[Configurable]] istrue , then- Throw a
TypeError exception.
- Throw a
- If resultDesc has a [[Writable]] field and resultDesc.[[Writable]] is
false , thenAssert : targetDesc has a [[Writable]] field.- If targetDesc.[[Writable]] is
true , throw aTypeError exception.
- If targetDesc is
- Return resultDesc.
[[GetOwnProperty]] for Proxy objects enforces the following invariants:
-
The result of [[GetOwnProperty]] must be either an Object or
undefined . - A property cannot be reported as non-existent, if it exists as a non-configurable own property of the target object.
- A property cannot be reported as non-existent, if it exists as an own property of a non-extensible target object.
- A property cannot be reported as existent, if it does not exist as an own property of the target object and the target object is not extensible.
- A property cannot be reported as non-configurable, unless it exists as a non-configurable own property of the target object.
- A property cannot be reported as both non-configurable and non-writable, unless it exists as a non-configurable, non-writable own property of the target object.
10.5.6 [[DefineOwnProperty]] ( P, Desc )
The [[DefineOwnProperty]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Let target be O.[[ProxyTarget]].
- Let handler be O.[[ProxyHandler]].
Assert : handleris an Object .- Let trap be ?
GetMethod (handler,"defineProperty" ). - If trap is
undefined , then- Return ? target.[[DefineOwnProperty]](P, Desc).
- Let descObj be
FromPropertyDescriptor (Desc). - Let booleanTrapResult be
ToBoolean (?Call (trap, handler, « target, P, descObj »)). - If booleanTrapResult is
false , returnfalse . - Let targetDesc be ? target.[[GetOwnProperty]](P).
- Let extensibleTarget be ?
IsExtensible (target). - If Desc has a [[Configurable]] field and Desc.[[Configurable]] is
false , then- Let settingConfigFalse be
true .
- Let settingConfigFalse be
- Else,
- Let settingConfigFalse be
false .
- Let settingConfigFalse be
- If targetDesc is
undefined , then- If extensibleTarget is
false , throw aTypeError exception. - If settingConfigFalse is
true , throw aTypeError exception.
- If extensibleTarget is
- Else,
- If
IsCompatiblePropertyDescriptor (extensibleTarget, Desc, targetDesc) isfalse , throw aTypeError exception. - If settingConfigFalse is
true and targetDesc.[[Configurable]] istrue , throw aTypeError exception. - If
IsDataDescriptor (targetDesc) istrue , targetDesc.[[Configurable]] isfalse , and targetDesc.[[Writable]] istrue , then- If Desc has a [[Writable]] field and Desc.[[Writable]] is
false , throw aTypeError exception.
- If Desc has a [[Writable]] field and Desc.[[Writable]] is
- If
- Return
true .
[[DefineOwnProperty]] for Proxy objects enforces the following invariants:
-
The result of [[DefineOwnProperty]]
is a Boolean value. - A property cannot be added, if the target object is not extensible.
- A property cannot be non-configurable, unless there exists a corresponding non-configurable own property of the target object.
- A non-configurable property cannot be non-writable, unless there exists a corresponding non-configurable, non-writable own property of the target object.
-
If a property has a corresponding target object property then applying the
Property Descriptor of the property to the target object using [[DefineOwnProperty]] will not throw an exception.
10.5.7 [[HasProperty]] ( P )
The [[HasProperty]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Let target be O.[[ProxyTarget]].
- Let handler be O.[[ProxyHandler]].
Assert : handleris an Object .- Let trap be ?
GetMethod (handler,"has" ). - If trap is
undefined , then- Return ? target.[[HasProperty]](P).
- Let booleanTrapResult be
ToBoolean (?Call (trap, handler, « target, P »)). - If booleanTrapResult is
false , then- Let targetDesc be ? target.[[GetOwnProperty]](P).
- If targetDesc is not
undefined , then- If targetDesc.[[Configurable]] is
false , throw aTypeError exception. - Let extensibleTarget be ?
IsExtensible (target). - If extensibleTarget is
false , throw aTypeError exception.
- If targetDesc.[[Configurable]] is
- Return booleanTrapResult.
[[HasProperty]] for Proxy objects enforces the following invariants:
-
The result of [[HasProperty]]
is a Boolean value. - A property cannot be reported as non-existent, if it exists as a non-configurable own property of the target object.
- A property cannot be reported as non-existent, if it exists as an own property of the target object and the target object is not extensible.
10.5.8 [[Get]] ( P, Receiver )
The [[Get]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Let target be O.[[ProxyTarget]].
- Let handler be O.[[ProxyHandler]].
Assert : handleris an Object .- Let trap be ?
GetMethod (handler,"get" ). - If trap is
undefined , then- Return ? target.[[Get]](P, Receiver).
- Let trapResult be ?
Call (trap, handler, « target, P, Receiver »). - Let targetDesc be ? target.[[GetOwnProperty]](P).
- If targetDesc is not
undefined and targetDesc.[[Configurable]] isfalse , then- If
IsDataDescriptor (targetDesc) istrue and targetDesc.[[Writable]] isfalse , then- If
SameValue (trapResult, targetDesc.[[Value]]) isfalse , throw aTypeError exception.
- If
- If
IsAccessorDescriptor (targetDesc) istrue and targetDesc.[[Get]] isundefined , then- If trapResult is not
undefined , throw aTypeError exception.
- If trapResult is not
- If
- Return trapResult.
[[Get]] for Proxy objects enforces the following invariants:
-
The value reported for a property must be the same as the value of the corresponding target object property if the target object property is a non-writable, non-configurable own
data property . -
The value reported for a property must be
undefined if the corresponding target object property is a non-configurable ownaccessor property that hasundefined as its [[Get]] attribute.
10.5.9 [[Set]] ( P, V, Receiver )
The [[Set]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Let target be O.[[ProxyTarget]].
- Let handler be O.[[ProxyHandler]].
Assert : handleris an Object .- Let trap be ?
GetMethod (handler,"set" ). - If trap is
undefined , then- Return ? target.[[Set]](P, V, Receiver).
- Let booleanTrapResult be
ToBoolean (?Call (trap, handler, « target, P, V, Receiver »)). - If booleanTrapResult is
false , returnfalse . - Let targetDesc be ? target.[[GetOwnProperty]](P).
- If targetDesc is not
undefined and targetDesc.[[Configurable]] isfalse , then- If
IsDataDescriptor (targetDesc) istrue and targetDesc.[[Writable]] isfalse , then- If
SameValue (V, targetDesc.[[Value]]) isfalse , throw aTypeError exception.
- If
- If
IsAccessorDescriptor (targetDesc) istrue , then- If targetDesc.[[Set]] is
undefined , throw aTypeError exception.
- If targetDesc.[[Set]] is
- If
- Return
true .
[[Set]] for Proxy objects enforces the following invariants:
-
The result of [[Set]]
is a Boolean value. -
Cannot change the value of a property to be different from the value of the corresponding target object property if the corresponding target object property is a non-writable, non-configurable own
data property . -
Cannot set the value of a property if the corresponding target object property is a non-configurable own
accessor property that hasundefined as its [[Set]] attribute.
10.5.10 [[Delete]] ( P )
The [[Delete]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Let target be O.[[ProxyTarget]].
- Let handler be O.[[ProxyHandler]].
Assert : handleris an Object .- Let trap be ?
GetMethod (handler,"deleteProperty" ). - If trap is
undefined , then- Return ? target.[[Delete]](P).
- Let booleanTrapResult be
ToBoolean (?Call (trap, handler, « target, P »)). - If booleanTrapResult is
false , returnfalse . - Let targetDesc be ? target.[[GetOwnProperty]](P).
- If targetDesc is
undefined , returntrue . - If targetDesc.[[Configurable]] is
false , throw aTypeError exception. - Let extensibleTarget be ?
IsExtensible (target). - If extensibleTarget is
false , throw aTypeError exception. - Return
true .
[[Delete]] for Proxy objects enforces the following invariants:
-
The result of [[Delete]]
is a Boolean value. - A property cannot be reported as deleted, if it exists as a non-configurable own property of the target object.
- A property cannot be reported as deleted, if it exists as an own property of the target object and the target object is non-extensible.
10.5.11 [[OwnPropertyKeys]] ( )
The [[OwnPropertyKeys]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Let target be O.[[ProxyTarget]].
- Let handler be O.[[ProxyHandler]].
Assert : handleris an Object .- Let trap be ?
GetMethod (handler,"ownKeys" ). - If trap is
undefined , then- Return ? target.[[OwnPropertyKeys]]().
- Let trapResultArray be ?
Call (trap, handler, « target »). - Let trapResult be ?
CreateListFromArrayLike (trapResultArray,property-key ). - If trapResult contains any duplicate entries, throw a
TypeError exception. - Let extensibleTarget be ?
IsExtensible (target). - Let targetKeys be ? target.[[OwnPropertyKeys]]().
Assert : targetKeys is aList ofproperty keys .Assert : targetKeys contains no duplicate entries.- Let targetConfigurableKeys be a new empty
List . - Let targetNonconfigurableKeys be a new empty
List . - For each element key of targetKeys, do
- Let desc be ? target.[[GetOwnProperty]](key).
- If desc is not
undefined and desc.[[Configurable]] isfalse , then- Append key to targetNonconfigurableKeys.
- Else,
- Append key to targetConfigurableKeys.
- If extensibleTarget is
true and targetNonconfigurableKeys is empty, then- Return trapResult.
- Let uncheckedResultKeys be a
List whose elements are the elements of trapResult. - For each element key of targetNonconfigurableKeys, do
- If uncheckedResultKeys does not contain key, throw a
TypeError exception. - Remove key from uncheckedResultKeys.
- If uncheckedResultKeys does not contain key, throw a
- If extensibleTarget is
true , return trapResult. - For each element key of targetConfigurableKeys, do
- If uncheckedResultKeys does not contain key, throw a
TypeError exception. - Remove key from uncheckedResultKeys.
- If uncheckedResultKeys does not contain key, throw a
- If uncheckedResultKeys is not empty, throw a
TypeError exception. - Return trapResult.
[[OwnPropertyKeys]] for Proxy objects enforces the following invariants:
-
The result of [[OwnPropertyKeys]] is a
List . -
The returned
List contains no duplicate entries. -
Each element of the returned
List is aproperty key . -
The result
List must contain the keys of all non-configurable own properties of the target object. -
If the target object is not extensible, then the result
List must contain all the keys of the own properties of the target object and no other values.
10.5.12 [[Call]] ( thisArgument, argumentsList )
The [[Call]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Let target be O.[[ProxyTarget]].
- Let handler be O.[[ProxyHandler]].
Assert : handleris an Object .- Let trap be ?
GetMethod (handler,"apply" ). - If trap is
undefined , then- Return ?
Call (target, thisArgument, argumentsList).
- Return ?
- Let argArray be
CreateArrayFromList (argumentsList). - Return ?
Call (trap, handler, « target, thisArgument, argArray »).
A
10.5.13 [[Construct]] ( argumentsList, newTarget )
The [[Construct]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Let target be O.[[ProxyTarget]].
Assert :IsConstructor (target) istrue .- Let handler be O.[[ProxyHandler]].
Assert : handleris an Object .- Let trap be ?
GetMethod (handler,"construct" ). - If trap is
undefined , then- Return ?
Construct (target, argumentsList, newTarget).
- Return ?
- Let argArray be
CreateArrayFromList (argumentsList). - Let newObj be ?
Call (trap, handler, « target, argArray, newTarget »). - If newObj
is not an Object , throw aTypeError exception. - Return newObj.
A
[[Construct]] for Proxy objects enforces the following invariants:
- The result of [[Construct]] must be an Object.
10.5.14 ValidateNonRevokedProxy ( proxy )
The abstract operation ValidateNonRevokedProxy takes argument proxy (a
- If proxy.[[ProxyTarget]] is
null , throw aTypeError exception. Assert : proxy.[[ProxyHandler]] is notnull .- Return
unused .
10.5.15 ProxyCreate ( target, handler )
The abstract operation ProxyCreate takes arguments target (an
- If target
is not an Object , throw aTypeError exception. - If handler
is not an Object , throw aTypeError exception. - Let P be
MakeBasicObject (« [[ProxyHandler]], [[ProxyTarget]] »). - Set P's essential internal methods, except for [[Call]] and [[Construct]], to the definitions specified in
10.5 . - If
IsCallable (target) istrue , then- Set P.[[Call]] as specified in
10.5.12 . - If
IsConstructor (target) istrue , then- Set P.[[Construct]] as specified in
10.5.13 .
- Set P.[[Construct]] as specified in
- Set P.[[Call]] as specified in
- Set P.[[ProxyTarget]] to target.
- Set P.[[ProxyHandler]] to handler.
- Return P.
11 ECMAScript Language: Source Text
11.1 Source Text
Syntax
ECMAScript source text is a sequence of Unicode code points. All Unicode code point values from U+0000 to U+10FFFF, including surrogate code points, may occur in ECMAScript source text where permitted by the ECMAScript grammars. The actual encodings used to store and interchange ECMAScript source text is not relevant to this specification. Regardless of the external source text encoding, a conforming ECMAScript implementation processes the source text as if it was an equivalent sequence of
The components of a combining character sequence are treated as individual Unicode code points even though a user might think of the whole sequence as a single character.
In string literals, regular expression literals, template literals and identifiers, any Unicode code point may also be expressed using Unicode escape sequences that explicitly express a code point's numeric value. Within a comment, such an escape sequence is effectively ignored as part of the comment.
ECMAScript differs from the Java programming language in the behaviour of Unicode escape sequences. In a Java program, if the Unicode escape sequence \u000A, for example, occurs within a single-line comment, it is interpreted as a line terminator (Unicode code point U+000A is LINE FEED (LF)) and therefore the next code point is not part of the comment. Similarly, if the Unicode escape sequence \u000A occurs within a string literal in a Java program, it is likewise interpreted as a line terminator, which is not allowed within a string literal—one must write \n instead of \u000A to cause a LINE FEED (LF) to be part of the value of a string literal. In an ECMAScript program, a Unicode escape sequence occurring within a comment is never interpreted and therefore cannot contribute to termination of the comment. Similarly, a Unicode escape sequence occurring within a string literal in an ECMAScript program always contributes to the literal and is never interpreted as a line terminator or as a code point that might terminate the string literal.
11.1.1 Static Semantics: UTF16EncodeCodePoint ( cp )
The abstract operation UTF16EncodeCodePoint takes argument cp (a Unicode code point) and returns a String. It performs the following steps when called:
Assert : 0 ≤ cp ≤ 0x10FFFF.- If cp ≤ 0xFFFF, return the String value consisting of the code unit whose numeric value is cp.
- Let cu1 be the code unit whose numeric value is
floor ((cp - 0x10000) / 0x400) + 0xD800. - Let cu2 be the code unit whose numeric value is ((cp - 0x10000)
modulo 0x400) + 0xDC00. - Return the
string-concatenation of cu1 and cu2.
11.1.2 Static Semantics: CodePointsToString ( text )
The abstract operation CodePointsToString takes argument text (a sequence of Unicode code points) and returns a String. It converts text into a String value, as described in
- Let result be the empty String.
- For each code point cp of text, do
- Set result to the
string-concatenation of result andUTF16EncodeCodePoint (cp).
- Set result to the
- Return result.
11.1.3 Static Semantics: UTF16SurrogatePairToCodePoint ( lead, trail )
The abstract operation UTF16SurrogatePairToCodePoint takes arguments lead (a code unit) and trail (a code unit) and returns a code point. Two code units that form a UTF-16
Assert : lead is aleading surrogate and trail is atrailing surrogate .- Let cp be (lead - 0xD800) × 0x400 + (trail - 0xDC00) + 0x10000.
- Return the code point cp.
11.1.4 Static Semantics: CodePointAt ( string, position )
The abstract operation CodePointAt takes arguments string (a String) and position (a non-negative
- Let size be the length of string.
Assert : position ≥ 0 and position < size.- Let first be the code unit at index position within string.
- Let cp be the code point whose numeric value is the numeric value of first.
- If first is neither a
leading surrogate nor atrailing surrogate , then- Return the
Record { [[CodePoint]]: cp, [[CodeUnitCount]]: 1, [[IsUnpairedSurrogate]]:false }.
- Return the
- If first is a
trailing surrogate or position + 1 = size, then- Return the
Record { [[CodePoint]]: cp, [[CodeUnitCount]]: 1, [[IsUnpairedSurrogate]]:true }.
- Return the
- Let second be the code unit at index position + 1 within string.
- If second is not a
trailing surrogate , then- Return the
Record { [[CodePoint]]: cp, [[CodeUnitCount]]: 1, [[IsUnpairedSurrogate]]:true }.
- Return the
- Set cp to
UTF16SurrogatePairToCodePoint (first, second). - Return the
Record { [[CodePoint]]: cp, [[CodeUnitCount]]: 2, [[IsUnpairedSurrogate]]:false }.
11.1.5 Static Semantics: StringToCodePoints ( string )
The abstract operation StringToCodePoints takes argument string (a String) and returns a
- Let codePoints be a new empty
List . - Let size be the length of string.
- Let position be 0.
- Repeat, while position < size,
- Let cp be
CodePointAt (string, position). - Append cp.[[CodePoint]] to codePoints.
- Set position to position + cp.[[CodeUnitCount]].
- Let cp be
- Return codePoints.
11.1.6 Static Semantics: ParseText ( sourceText, goalSymbol )
The abstract operation ParseText takes arguments sourceText (a String or a sequence of Unicode code points) and goalSymbol (a nonterminal in one of the ECMAScript grammars) and returns a
- If sourceText
is a String , set sourceText toStringToCodePoints (sourceText). - Attempt to parse sourceText using goalSymbol as the
goal symbol , and analyse the parse result for anyearly error conditions. Parsing andearly error detection may be interleaved in animplementation-defined manner. - If the parse succeeded and no
early errors were found, return theParse Node (an instance of goalSymbol) at the root of the parse tree resulting from the parse. - Otherwise, return a
List of one or moreSyntaxError objects representing the parsing errors and/orearly errors . If more than one parsing error orearly error is present, the number and ordering of error objects in the list isimplementation-defined , but at least one must be present.
Consider a text that has an
See also clause
11.2 Types of Source Code
There are four types of ECMAScript code:
-
Global code is source text that is treated as an ECMAScript
Script . The global code of a particularScript does not include any source text that is parsed as part of aFunctionDeclaration ,FunctionExpression ,GeneratorDeclaration ,GeneratorExpression ,AsyncFunctionDeclaration ,AsyncFunctionExpression ,AsyncGeneratorDeclaration ,AsyncGeneratorExpression ,MethodDefinition ,ArrowFunction ,AsyncArrowFunction ,ClassDeclaration , orClassExpression . -
Eval code is the source text supplied to the built-in
evalfunction. More precisely, if the parameter to the built-inevalfunctionis a String , it is treated as an ECMAScriptScript . The eval code for a particular invocation ofevalis the global code portion of thatScript . -
Function code is source text that is parsed to supply the value of the [[ECMAScriptCode]] and [[FormalParameters]] internal slots (see
10.2 ) of an ECMAScriptfunction object . The function code of a particular ECMAScript function does not include any source text that is parsed as the function code of a nestedFunctionDeclaration ,FunctionExpression ,GeneratorDeclaration ,GeneratorExpression ,AsyncFunctionDeclaration ,AsyncFunctionExpression ,AsyncGeneratorDeclaration ,AsyncGeneratorExpression ,MethodDefinition ,ArrowFunction ,AsyncArrowFunction ,ClassDeclaration , orClassExpression .In addition, if the source text referred to above is parsed as:
- the
FormalParameters andFunctionBody of aFunctionDeclaration orFunctionExpression , - the
FormalParameters andGeneratorBody of aGeneratorDeclaration orGeneratorExpression , - the
FormalParameters andAsyncFunctionBody of anAsyncFunctionDeclaration orAsyncFunctionExpression , or - the
FormalParameters andAsyncGeneratorBody of anAsyncGeneratorDeclaration orAsyncGeneratorExpression ,
then the
source text matched by theBindingIdentifier (if any) of that declaration or expression is also included in the function code of the corresponding function. - the
-
Module code is source text that is code that is provided as a
ModuleBody . It is the code that is directly evaluated when a module is initialized. The module code of a particular module does not include any source text that is parsed as part of a nestedFunctionDeclaration ,FunctionExpression ,GeneratorDeclaration ,GeneratorExpression ,AsyncFunctionDeclaration ,AsyncFunctionExpression ,AsyncGeneratorDeclaration ,AsyncGeneratorExpression ,MethodDefinition ,ArrowFunction ,AsyncArrowFunction ,ClassDeclaration , orClassExpression .
Function code is generally provided as the bodies of Function Definitions (
The practical effect of including the
11.2.1 Directive Prologues and the Use Strict Directive
A Directive Prologue is the longest sequence of
A Use Strict Directive is an "use strict" or 'use strict'. A
A
The
11.2.2 Strict Mode Code
An ECMAScript syntactic unit may be processed using either unrestricted or strict mode syntax and semantics (
-
Global code is strict mode code if it begins with aDirective Prologue that contains aUse Strict Directive . -
Module code is always strict mode code. -
All parts of a
ClassDeclaration or aClassExpression are strict mode code. -
Eval code is strict mode code if it begins with aDirective Prologue that contains aUse Strict Directive or if the call toevalis adirect eval that is contained in strict mode code. -
Function code is strict mode code if the associatedFunctionDeclaration ,FunctionExpression ,GeneratorDeclaration ,GeneratorExpression ,AsyncFunctionDeclaration ,AsyncFunctionExpression ,AsyncGeneratorDeclaration ,AsyncGeneratorExpression ,MethodDefinition ,ArrowFunction , orAsyncArrowFunction is contained in strict mode code or if the code that produces the value of the function's [[ECMAScriptCode]] internal slot begins with aDirective Prologue that contains aUse Strict Directive . -
Function code that is supplied as the arguments to the built-in Function, Generator, AsyncFunction, and AsyncGeneratorconstructors is strict mode code if the last argumentis a String that when processed is aFunctionBody that begins with aDirective Prologue that contains aUse Strict Directive .
ECMAScript code that is not strict mode code is called non-strict code.
11.2.2.1 Static Semantics: IsStrict ( node )
The abstract operation IsStrict takes argument node (a
- If the
source text matched by node isstrict mode code , returntrue ; else returnfalse .
11.2.3 Non-ECMAScript Functions
An ECMAScript implementation may support the evaluation of function
12 ECMAScript Language: Lexical Grammar
The source text of an ECMAScript
There are several situations where the identification of lexical input elements is sensitive to the syntactic grammar context that is consuming the input elements. This requires multiple
The use of multiple lexical goals ensures that there are no lexical ambiguities that would affect automatic semicolon insertion. For example, there are no syntactic grammar contexts where both a leading division or division-assignment, and a leading
a = b
/hi/g.exec(c).map(d);where the first non-whitespace, non-comment code point after a
a = b / hi / g.exec(c).map(d);Syntax
12.1 Unicode Format-Control Characters
The Unicode format-control characters (i.e., the characters in category “Cf” in the Unicode Character Database such as LEFT-TO-RIGHT MARK or RIGHT-TO-LEFT MARK) are control codes used to control the formatting of a range of text in the absence of higher-level protocols for this (such as mark-up languages).
It is useful to allow format-control characters in source text to facilitate editing and display. All format control characters may be used within comments, and within string literals, template literals, and regular expression literals.
U+FEFF (ZERO WIDTH NO-BREAK SPACE) is a format-control character used primarily at the start of a text to mark it as Unicode and to allow detection of the text's encoding and byte order. <ZWNBSP> characters intended for this purpose can sometimes also appear after the start of a text, for example as a result of concatenating files. In
12.2 White Space
White space code points are used to improve source text readability and to separate tokens (indivisible lexical units) from each other, but are otherwise insignificant. White space code points may occur between any two tokens and at the start or end of input. White space code points may occur within a
The ECMAScript white space code points are listed in
| Code Points | Name | Abbreviation |
|---|---|---|
U+0009
|
CHARACTER TABULATION | <TAB> |
U+000B
|
LINE TABULATION | <VT> |
U+000C
|
FORM FEED (FF) | <FF> |
U+FEFF
|
ZERO WIDTH NO-BREAK SPACE | <ZWNBSP> |
| any code point in general category “Space_Separator” | <USP> |
U+0020 (SPACE) and U+00A0 (NO-BREAK SPACE) code points are part of <USP>.
Other than for the code points listed in
Syntax
12.3 Line Terminators
Like white space code points, line terminator code points are used to improve source text readability and to separate tokens (indivisible lexical units) from each other. However, unlike white space code points, line terminators have some influence over the behaviour of the syntactic grammar. In general, line terminators may occur between any two tokens, but there are a few places where they are forbidden by the syntactic grammar. Line terminators also affect the process of automatic semicolon insertion (
A line terminator can occur within a
Line terminators are included in the set of white space code points that are matched by the \s class in regular expressions.
The ECMAScript line terminator code points are listed in
| Code Point | Unicode Name | Abbreviation |
|---|---|---|
U+000A
|
LINE FEED (LF) | <LF> |
U+000D
|
CARRIAGE RETURN (CR) | <CR> |
U+2028
|
LINE SEPARATOR | <LS> |
U+2029
|
PARAGRAPH SEPARATOR | <PS> |
Only the Unicode code points in
Syntax
12.4 Comments
Comments can be either single or multi-line. Multi-line comments cannot nest.
Because a single-line comment can contain any Unicode code point except a // marker to the end of the line. However, the
Comments behave like white space and are discarded except that, if a
Syntax
A number of productions in this section are given alternative definitions in section
12.5 Hashbang Comments
Hashbang Comments are location-sensitive and like other types of comments are discarded from the stream of input elements for the syntactic grammar.
Syntax
12.6 Tokens
Syntax
The
12.7 Names and Keywords
This standard specifies specific code point additions: U+0024 (DOLLAR SIGN) and U+005F (LOW LINE) are permitted anywhere in an
Syntax
The definitions of the nonterminal
The nonterminal _ via
The sets of code points with Unicode properties “ID_Start” and “ID_Continue” include, respectively, the code points with Unicode properties “Other_ID_Start” and “Other_ID_Continue”.
12.7.1 Identifier Names
Unicode escape sequences are permitted in an \ preceding the \
Two
12.7.1.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
IdentifierCodePoint ofUnicodeEscapeSequence is not some Unicode code point matched by theIdentifierStartChar lexical grammar production.
-
It is a Syntax Error if the
IdentifierCodePoint ofUnicodeEscapeSequence is not some Unicode code point matched by theIdentifierPartChar lexical grammar production.
12.7.1.2 Static Semantics: IdentifierCodePoints
The
- Let cp be the
IdentifierCodePoint ofIdentifierStart . - Return « cp ».
- Let cps be the
IdentifierCodePoints of the derivedIdentifierName . - Let cp be the
IdentifierCodePoint ofIdentifierPart . - Return the
list-concatenation of cps and « cp ».
12.7.1.3 Static Semantics: IdentifierCodePoint
The
- Return the code point matched by
IdentifierStartChar .
- Return the code point matched by
IdentifierPartChar .
- Return the code point whose numeric value is the MV of
Hex4Digits .
- Return the code point whose numeric value is the MV of
CodePoint .
12.7.2 Keywords and Reserved Words
A keyword is a token that matches fixed width font, in some syntactic production. The keywords of ECMAScript include if, while, async, await, and many others.
A reserved word is an if and while are reserved words. await is reserved only inside async functions and modules. async is not reserved; it can be used as a variable name or statement label without restriction.
This specification uses a combination of grammatical productions and await and yield, are unconditionally reserved. Exceptions for await and yield are specified in
-
Those that are always allowed as identifiers, and are not keywords, such as
Math,window,toString, and_; -
Those that are never allowed as identifiers, namely the
ReservedWord s listed below exceptawaitandyield; -
Those that are contextually allowed as identifiers, namely
awaitandyield; -
Those that are contextually disallowed as identifiers, in
strict mode code :let,static,implements,interface,package,private,protected, andpublic; -
Those that are always allowed as identifiers, but also appear as keywords within certain syntactic productions, at places where
Identifier is not allowed:as,async,from,get,meta,of,set, andtarget.
The term conditional keyword, or contextual keyword, is sometimes used to refer to the keywords that fall in the last three categories, and thus can be used as identifiers in some contexts and as keywords in others.
Syntax
Per \
An \ els\u{65}. The
enum is not currently used as a keyword in this specification. It is a future reserved word, set aside for use as a keyword in future language extensions.
Similarly, implements, interface, package, private, protected, and public are future reserved words in
12.8 Punctuators
Syntax
12.9 Literals
12.9.1 Null Literals
Syntax
12.9.2 Boolean Literals
Syntax
12.9.3 Numeric Literals
Syntax
The
For example: 3in is an error and not the two input elements 3 and in.
12.9.3.1 Static Semantics: Early Errors
- It is a Syntax Error if
IsStrict (this production) istrue .
12.9.3.2 Static Semantics: MV
A numeric literal stands for a value of the
-
The MV of
DecimalLiteral :: DecimalIntegerLiteral . DecimalDigits DecimalIntegerLiteral plus (the MV ofDecimalDigits × 10-n), where n is the number of code points inDecimalDigits , excluding all occurrences ofNumericLiteralSeparator . -
The MV of
DecimalLiteral :: DecimalIntegerLiteral . ExponentPart DecimalIntegerLiteral × 10e, where e is the MV ofExponentPart . -
The MV of
DecimalLiteral :: DecimalIntegerLiteral . DecimalDigits ExponentPart DecimalIntegerLiteral plus (the MV ofDecimalDigits × 10-n)) × 10e, where n is the number of code points inDecimalDigits , excluding all occurrences ofNumericLiteralSeparator and e is the MV ofExponentPart . -
The MV of
DecimalLiteral :: . DecimalDigits DecimalDigits × 10-n, where n is the number of code points inDecimalDigits , excluding all occurrences ofNumericLiteralSeparator . -
The MV of
DecimalLiteral :: . DecimalDigits ExponentPart DecimalDigits × 10e - n, where n is the number of code points inDecimalDigits , excluding all occurrences ofNumericLiteralSeparator , and e is the MV ofExponentPart . -
The MV of
DecimalLiteral :: DecimalIntegerLiteral ExponentPart DecimalIntegerLiteral × 10e, where e is the MV ofExponentPart . -
The MV of
DecimalIntegerLiteral :: 0 -
The MV of
DecimalIntegerLiteral :: NonZeroDigit NumericLiteralSeparator opt DecimalDigits NonZeroDigit × 10n) plus the MV ofDecimalDigits , where n is the number of code points inDecimalDigits , excluding all occurrences ofNumericLiteralSeparator . -
The MV of
DecimalDigits :: DecimalDigits DecimalDigit DecimalDigits × 10) plus the MV ofDecimalDigit . -
The MV of
DecimalDigits :: DecimalDigits NumericLiteralSeparator DecimalDigit DecimalDigits × 10) plus the MV ofDecimalDigit . -
The MV of
ExponentPart :: ExponentIndicator SignedInteger SignedInteger . -
The MV of
SignedInteger :: - DecimalDigits DecimalDigits . -
The MV of
DecimalDigit :: 0 HexDigit :: 0 OctalDigit :: 0 LegacyOctalEscapeSequence :: 0 BinaryDigit :: 0 -
The MV of
DecimalDigit :: 1 NonZeroDigit :: 1 HexDigit :: 1 OctalDigit :: 1 BinaryDigit :: 1 -
The MV of
DecimalDigit :: 2 NonZeroDigit :: 2 HexDigit :: 2 OctalDigit :: 2 -
The MV of
DecimalDigit :: 3 NonZeroDigit :: 3 HexDigit :: 3 OctalDigit :: 3 -
The MV of
DecimalDigit :: 4 NonZeroDigit :: 4 HexDigit :: 4 OctalDigit :: 4 -
The MV of
DecimalDigit :: 5 NonZeroDigit :: 5 HexDigit :: 5 OctalDigit :: 5 -
The MV of
DecimalDigit :: 6 NonZeroDigit :: 6 HexDigit :: 6 OctalDigit :: 6 -
The MV of
DecimalDigit :: 7 NonZeroDigit :: 7 HexDigit :: 7 OctalDigit :: 7 -
The MV of
DecimalDigit :: 8 NonZeroDigit :: 8 NonOctalDigit :: 8 HexDigit :: 8 -
The MV of
DecimalDigit :: 9 NonZeroDigit :: 9 NonOctalDigit :: 9 HexDigit :: 9 -
The MV of
HexDigit :: a HexDigit :: A -
The MV of
HexDigit :: b HexDigit :: B -
The MV of
HexDigit :: c HexDigit :: C -
The MV of
HexDigit :: d HexDigit :: D -
The MV of
HexDigit :: e HexDigit :: E -
The MV of
HexDigit :: f HexDigit :: F -
The MV of
BinaryDigits :: BinaryDigits BinaryDigit BinaryDigits × 2) plus the MV ofBinaryDigit . -
The MV of
BinaryDigits :: BinaryDigits NumericLiteralSeparator BinaryDigit BinaryDigits × 2) plus the MV ofBinaryDigit . -
The MV of
OctalDigits :: OctalDigits OctalDigit OctalDigits × 8) plus the MV ofOctalDigit . -
The MV of
OctalDigits :: OctalDigits NumericLiteralSeparator OctalDigit OctalDigits × 8) plus the MV ofOctalDigit . -
The MV of
LegacyOctalIntegerLiteral :: LegacyOctalIntegerLiteral OctalDigit LegacyOctalIntegerLiteral times 8) plus the MV ofOctalDigit . -
The MV of
NonOctalDecimalIntegerLiteral :: LegacyOctalLikeDecimalIntegerLiteral NonOctalDigit LegacyOctalLikeDecimalIntegerLiteral times 10) plus the MV ofNonOctalDigit . -
The MV of
NonOctalDecimalIntegerLiteral :: NonOctalDecimalIntegerLiteral DecimalDigit NonOctalDecimalIntegerLiteral times 10) plus the MV ofDecimalDigit . -
The MV of
LegacyOctalLikeDecimalIntegerLiteral :: LegacyOctalLikeDecimalIntegerLiteral OctalDigit LegacyOctalLikeDecimalIntegerLiteral times 10) plus the MV ofOctalDigit . -
The MV of
HexDigits :: HexDigits HexDigit HexDigits × 16) plus the MV ofHexDigit . -
The MV of
HexDigits :: HexDigits NumericLiteralSeparator HexDigit HexDigits × 16) plus the MV ofHexDigit .
12.9.3.3 Static Semantics: NumericValue
The
- Return
RoundMVResult (MV ofDecimalLiteral ).
- Return
𝔽 (MV ofNonDecimalIntegerLiteral ).
- Return
𝔽 (MV ofLegacyOctalIntegerLiteral ).
- Return the
BigInt value for the MV ofNonDecimalIntegerLiteral .
- Return
0 ℤ.
- Return the
BigInt value for the MV ofNonZeroDigit .
- Let n be the number of code points in
DecimalDigits , excluding all occurrences ofNumericLiteralSeparator . - Let mv be (the MV of
NonZeroDigit × 10n) plus the MV ofDecimalDigits . - Return
ℤ (mv).
12.9.4 String Literals
A string literal is 0 or more Unicode code points enclosed in single or double quotes. Unicode code points may also be represented by an escape sequence. All code points may appear literally in a string literal except for the closing quote code points, U+005C (REVERSE SOLIDUS), U+000D (CARRIAGE RETURN), and U+000A (LINE FEED). Any code points may appear in the form of an escape sequence. String literals evaluate to ECMAScript String values. When generating these String values Unicode code points are UTF-16 encoded as defined in
Syntax
The definition of the nonterminal
<LF> and <CR> cannot appear in a string literal, except as part of a \n or \u000A.
12.9.4.1 Static Semantics: Early Errors
- It is a Syntax Error if
IsStrict (this production) istrue .
It is possible for string literals to precede a
function invalid() { "\7"; "use strict"; }12.9.4.2 Static Semantics: SV
The
A string literal stands for a value of the
-
The SV of
StringLiteral :: " " -
The SV of
StringLiteral :: ' ' -
The SV of
DoubleStringCharacters :: DoubleStringCharacter DoubleStringCharacters string-concatenation of the SV ofDoubleStringCharacter and the SV ofDoubleStringCharacters . -
The SV of
SingleStringCharacters :: SingleStringCharacter SingleStringCharacters string-concatenation of the SV ofSingleStringCharacter and the SV ofSingleStringCharacters . -
The SV of
DoubleStringCharacter :: SourceCharacter but not one of " or\ orLineTerminator UTF16EncodeCodePoint on the code point matched bySourceCharacter . -
The SV of
DoubleStringCharacter :: <LS> -
The SV of
DoubleStringCharacter :: <PS> -
The SV of
DoubleStringCharacter :: LineContinuation -
The SV of
SingleStringCharacter :: SourceCharacter but not one of ' or\ orLineTerminator UTF16EncodeCodePoint on the code point matched bySourceCharacter . -
The SV of
SingleStringCharacter :: <LS> -
The SV of
SingleStringCharacter :: <PS> -
The SV of
SingleStringCharacter :: LineContinuation -
The SV of
EscapeSequence :: 0 -
The SV of
CharacterEscapeSequence :: SingleEscapeCharacter SingleEscapeCharacter according toTable 37 .
| Escape Sequence | Code Unit Value | Unicode Character Name | Symbol |
|---|---|---|---|
\b
|
0x0008
|
BACKSPACE | <BS> |
\t
|
0x0009
|
CHARACTER TABULATION | <HT> |
\n
|
0x000A
|
LINE FEED (LF) | <LF> |
\v
|
0x000B
|
LINE TABULATION | <VT> |
\f
|
0x000C
|
FORM FEED (FF) | <FF> |
\r
|
0x000D
|
CARRIAGE RETURN (CR) | <CR> |
\"
|
0x0022
|
QUOTATION MARK |
"
|
\'
|
0x0027
|
APOSTROPHE |
'
|
\\
|
0x005C
|
REVERSE SOLIDUS |
\
|
-
The SV of
NonEscapeCharacter :: SourceCharacter but not one of EscapeCharacter orLineTerminator UTF16EncodeCodePoint on the code point matched bySourceCharacter . -
The SV of
EscapeSequence :: LegacyOctalEscapeSequence LegacyOctalEscapeSequence . -
The SV of
NonOctalDecimalEscapeSequence :: 8 -
The SV of
NonOctalDecimalEscapeSequence :: 9 -
The SV of
HexEscapeSequence :: x HexDigit HexDigit HexEscapeSequence . -
The SV of
Hex4Digits :: HexDigit HexDigit HexDigit HexDigit Hex4Digits . -
The SV of
UnicodeEscapeSequence :: u{ CodePoint } UTF16EncodeCodePoint on the MV ofCodePoint . -
The SV of
TemplateEscapeSequence :: 0
12.9.4.3 Static Semantics: MV
-
The MV of
LegacyOctalEscapeSequence :: ZeroToThree OctalDigit ZeroToThree ) plus the MV ofOctalDigit . -
The MV of
LegacyOctalEscapeSequence :: FourToSeven OctalDigit FourToSeven ) plus the MV ofOctalDigit . -
The MV of
LegacyOctalEscapeSequence :: ZeroToThree OctalDigit OctalDigit ZeroToThree ) plus (8 times the MV of the firstOctalDigit ) plus the MV of the secondOctalDigit . -
The MV of
ZeroToThree :: 0 -
The MV of
ZeroToThree :: 1 -
The MV of
ZeroToThree :: 2 -
The MV of
ZeroToThree :: 3 -
The MV of
FourToSeven :: 4 -
The MV of
FourToSeven :: 5 -
The MV of
FourToSeven :: 6 -
The MV of
FourToSeven :: 7 -
The MV of
HexEscapeSequence :: x HexDigit HexDigit HexDigit ) plus the MV of the secondHexDigit . -
The MV of
Hex4Digits :: HexDigit HexDigit HexDigit HexDigit HexDigit ) plus (0x100 × the MV of the secondHexDigit ) plus (0x10 × the MV of the thirdHexDigit ) plus the MV of the fourthHexDigit .
12.9.5 Regular Expression Literals
A regular expression literal is an input element that is converted to a RegExp object (see === to each other even if the two literals' contents are identical. A RegExp object may also be created at runtime by new RegExp or calling the RegExp
The productions below describe the syntax for a regular expression literal and are used by the input element scanner to find the end of the regular expression literal. The source text comprising the
An implementation may extend the ECMAScript Regular Expression grammar defined in
Syntax
Regular expression literals may not be empty; instead of representing an empty regular expression literal, the code unit sequence // starts a single-line comment. To specify an empty regular expression, use: /(?:)/.
12.9.5.1 Static Semantics: BodyText
The
- Return the source text that was recognized as
RegularExpressionBody .
12.9.5.2 Static Semantics: FlagText
The
- Return the source text that was recognized as
RegularExpressionFlags .
12.9.6 Template Literal Lexical Components
Syntax
12.9.6.1 Static Semantics: TV
The
-
The TV of
NoSubstitutionTemplate :: ` ` -
The TV of
TemplateHead :: ` ${ -
The TV of
TemplateMiddle :: } ${ -
The TV of
TemplateTail :: } ` -
The TV of
TemplateCharacters :: TemplateCharacter TemplateCharacters undefined if the TV ofTemplateCharacter isundefined or the TV ofTemplateCharacters isundefined . Otherwise, it is thestring-concatenation of the TV ofTemplateCharacter and the TV ofTemplateCharacters . -
The TV of
TemplateCharacter :: SourceCharacter but not one of ` or\ or$ orLineTerminator UTF16EncodeCodePoint on the code point matched bySourceCharacter . -
The TV of
TemplateCharacter :: $ -
The TV of
TemplateCharacter :: \ TemplateEscapeSequence SV ofTemplateEscapeSequence . -
The TV of
TemplateCharacter :: \ NotEscapeSequence undefined . -
The TV of
TemplateCharacter :: LineTerminatorSequence TRV ofLineTerminatorSequence . -
The TV of
LineContinuation :: \ LineTerminatorSequence
12.9.6.2 Static Semantics: TRV
The
-
The TRV of
NoSubstitutionTemplate :: ` ` -
The TRV of
TemplateHead :: ` ${ -
The TRV of
TemplateMiddle :: } ${ -
The TRV of
TemplateTail :: } ` -
The TRV of
TemplateCharacters :: TemplateCharacter TemplateCharacters string-concatenation of the TRV ofTemplateCharacter and the TRV ofTemplateCharacters . -
The TRV of
TemplateCharacter :: SourceCharacter but not one of ` or\ or$ orLineTerminator UTF16EncodeCodePoint on the code point matched bySourceCharacter . -
The TRV of
TemplateCharacter :: $ -
The TRV of
TemplateCharacter :: \ TemplateEscapeSequence string-concatenation of the code unit 0x005C (REVERSE SOLIDUS) and the TRV ofTemplateEscapeSequence . -
The TRV of
TemplateCharacter :: \ NotEscapeSequence string-concatenation of the code unit 0x005C (REVERSE SOLIDUS) and the TRV ofNotEscapeSequence . -
The TRV of
TemplateEscapeSequence :: 0 -
The TRV of
NotEscapeSequence :: 0 DecimalDigit string-concatenation of the code unit 0x0030 (DIGIT ZERO) and the TRV ofDecimalDigit . -
The TRV of
NotEscapeSequence :: x [lookahead ∉ HexDigit ] -
The TRV of
NotEscapeSequence :: x HexDigit [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0078 (LATIN SMALL LETTER X) and the TRV ofHexDigit . -
The TRV of
NotEscapeSequence :: u [lookahead ∉ HexDigit ][lookahead ≠ { ] -
The TRV of
NotEscapeSequence :: u HexDigit [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U) and the TRV ofHexDigit . -
The TRV of
NotEscapeSequence :: u HexDigit HexDigit [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U), the TRV of the firstHexDigit , and the TRV of the secondHexDigit . -
The TRV of
NotEscapeSequence :: u HexDigit HexDigit HexDigit [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U), the TRV of the firstHexDigit , the TRV of the secondHexDigit , and the TRV of the thirdHexDigit . -
The TRV of
NotEscapeSequence :: u { [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U) and the code unit 0x007B (LEFT CURLY BRACKET). -
The TRV of
NotEscapeSequence :: u { NotCodePoint [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U), the code unit 0x007B (LEFT CURLY BRACKET), and the TRV ofNotCodePoint . -
The TRV of
NotEscapeSequence :: u { CodePoint [lookahead ∉ HexDigit ][lookahead ≠ } ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U), the code unit 0x007B (LEFT CURLY BRACKET), and the TRV ofCodePoint . -
The TRV of
DecimalDigit :: one of 0 1 2 3 4 5 6 7 8 9 UTF16EncodeCodePoint on the single code point matched by this production. -
The TRV of
CharacterEscapeSequence :: NonEscapeCharacter SV ofNonEscapeCharacter . -
The TRV of
SingleEscapeCharacter :: one of ' " \ b f n r t v UTF16EncodeCodePoint on the single code point matched by this production. -
The TRV of
HexEscapeSequence :: x HexDigit HexDigit string-concatenation of the code unit 0x0078 (LATIN SMALL LETTER X), the TRV of the firstHexDigit , and the TRV of the secondHexDigit . -
The TRV of
UnicodeEscapeSequence :: u Hex4Digits string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U) and the TRV ofHex4Digits . -
The TRV of
UnicodeEscapeSequence :: u{ CodePoint } string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U), the code unit 0x007B (LEFT CURLY BRACKET), the TRV ofCodePoint , and the code unit 0x007D (RIGHT CURLY BRACKET). -
The TRV of
Hex4Digits :: HexDigit HexDigit HexDigit HexDigit string-concatenation of the TRV of the firstHexDigit , the TRV of the secondHexDigit , the TRV of the thirdHexDigit , and the TRV of the fourthHexDigit . -
The TRV of
HexDigits :: HexDigits HexDigit string-concatenation of the TRV ofHexDigits and the TRV ofHexDigit . -
The TRV of
HexDigit :: one of 0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F UTF16EncodeCodePoint on the single code point matched by this production. -
The TRV of
LineContinuation :: \ LineTerminatorSequence string-concatenation of the code unit 0x005C (REVERSE SOLIDUS) and the TRV ofLineTerminatorSequence . -
The TRV of
LineTerminatorSequence :: <LF> -
The TRV of
LineTerminatorSequence :: <CR> -
The TRV of
LineTerminatorSequence :: <LS> -
The TRV of
LineTerminatorSequence :: <PS> -
The TRV of
LineTerminatorSequence :: <CR> <LF>
12.10 Automatic Semicolon Insertion
Most ECMAScript statements and declarations must be terminated with a semicolon. Such semicolons may always appear explicitly in the source text. For convenience, however, such semicolons may be omitted from the source text in certain situations. These situations are described by saying that semicolons are automatically inserted into the source code token stream in those situations.
12.10.1 Rules of Automatic Semicolon Insertion
In the following rules, “token” means the actual recognized lexical token determined using the current lexical
There are three basic rules of semicolon insertion:
-
When, as the source text is parsed from left to right, a token (called the offending token) is encountered that is not allowed by any production of the grammar, then a semicolon is automatically inserted before the offending token if one or more of the following conditions is true:
-
The offending token is separated from the previous token by at least one
LineTerminator . -
The offending token is
}. -
The previous token is
)and the inserted semicolon would then be parsed as the terminating semicolon of a do-while statement (14.7.2 ).
-
The offending token is separated from the previous token by at least one
- When, as the source text is parsed from left to right, the end of the input stream of tokens is encountered and the parser is unable to parse the input token stream as a single instance of the goal nonterminal, then a semicolon is automatically inserted at the end of the input stream.
-
When, as the source text is parsed from left to right, a token is encountered that is allowed by some production of the grammar, but the production is a restricted production and the token would be the first token for a terminal or nonterminal immediately following the annotation “[no
LineTerminator here]” within the restricted production (and therefore such a token is called a restricted token), and the restricted token is separated from the previous token by at least oneLineTerminator , then a semicolon is automatically inserted before the restricted token.
However, there is an additional overriding condition on the preceding rules: a semicolon is never inserted automatically if the semicolon would then be parsed as an empty statement or if that semicolon would become one of the two semicolons in the header of a for statement (see
The following are the only restricted productions in the grammar:
The practical effect of these restricted productions is as follows:
-
When a
++or--token is encountered where the parser would treat it as a postfix operator, and at least oneLineTerminator occurred between the preceding token and the++or--token, then a semicolon is automatically inserted before the++or--token. -
When a
continue,break,return,throw, oryieldtoken is encountered and aLineTerminator is encountered before the next token, a semicolon is automatically inserted after thecontinue,break,return,throw, oryieldtoken. -
When arrow function parameter(s) are followed by a
LineTerminator before a=>token, a semicolon is automatically inserted and the punctuator causes a syntax error. -
When an
asynctoken is followed by aLineTerminator before afunctionorIdentifierName or(token, a semicolon is automatically inserted and theasynctoken is not treated as part of the same expression or class element as the following tokens. -
When an
asynctoken is followed by aLineTerminator before a*token, a semicolon is automatically inserted and the punctuator causes a syntax error.
The resulting practical advice to ECMAScript programmers is:
-
A postfix
++or--operator should be on the same line as its operand. -
An
Expression in areturnorthrowstatement or anAssignmentExpression in ayieldexpression should start on the same line as thereturn,throw, oryieldtoken. -
A
LabelIdentifier in abreakorcontinuestatement should be on the same line as thebreakorcontinuetoken. -
The end of an arrow function's parameter(s) and its
=>should be on the same line. -
The
asynctoken preceding an asynchronous function or method should be on the same line as the immediately following token.
12.10.2 Examples of Automatic Semicolon Insertion
This section is non-normative.The source
{ 1 2 } 3is not a valid sentence in the ECMAScript grammar, even with the automatic semicolon insertion rules. In contrast, the source
{ 1
2 } 3is also not a valid ECMAScript sentence, but is transformed by automatic semicolon insertion into the following:
{ 1
;2 ;} 3;which is a valid ECMAScript sentence.
The source
for (a; b
)is not a valid ECMAScript sentence and is not altered by automatic semicolon insertion because the semicolon is needed for the header of a for statement. Automatic semicolon insertion never inserts one of the two semicolons in the header of a for statement.
The source
return
a + bis transformed by automatic semicolon insertion into the following:
return;
a + b;The expression a + b is not treated as a value to be returned by the return statement, because a return.
The source
a = b
++cis transformed by automatic semicolon insertion into the following:
a = b;
++c;The token ++ is not treated as a postfix operator applying to the variable b, because a b and ++.
The source
if (a > b)
else c = dis not a valid ECMAScript sentence and is not altered by automatic semicolon insertion before the else token, even though no production of the grammar applies at that point, because an automatically inserted semicolon would then be parsed as an empty statement.
The source
a = b + c
(d + e).print()is not transformed by automatic semicolon insertion, because the parenthesized expression that begins the second line can be interpreted as an argument list for a function call:
a = b + c(d + e).print()In the circumstance that an assignment statement must begin with a left parenthesis, it is a good idea for the programmer to provide an explicit semicolon at the end of the preceding statement rather than to rely on automatic semicolon insertion.
12.10.3 Interesting Cases of Automatic Semicolon Insertion
This section is non-normative.ECMAScript programs can be written in a style with very few semicolons by relying on automatic semicolon insertion. As described above, semicolons are not inserted at every newline, and automatic semicolon insertion can depend on multiple tokens across line terminators.
As new syntactic features are added to ECMAScript, additional grammar productions could be added that cause lines relying on automatic semicolon insertion preceding them to change grammar productions when parsed.
For the purposes of this section, a case of automatic semicolon insertion is considered interesting if it is a place where a semicolon may or may not be inserted, depending on the source text which precedes it. The rest of this section describes a number of interesting cases of automatic semicolon insertion in this version of ECMAScript.
12.10.3.1 Interesting Cases of Automatic Semicolon Insertion in Statement Lists
In a
- An opening parenthesis (
(). Without a semicolon, the two lines together are treated as aCallExpression . - An opening square bracket (
[). Without a semicolon, the two lines together are treated as property access, rather than anArrayLiteral orArrayAssignmentPattern . - A template literal (
`). Without a semicolon, the two lines together are interpreted as a tagged Template (13.3.11 ), with the previous expression as theMemberExpression . - Unary
+or-. Without a semicolon, the two lines together are interpreted as a usage of the corresponding binary operator. - A RegExp literal. Without a semicolon, the two lines together may be parsed instead as the
/MultiplicativeOperator , for example if the RegExp has flags.
12.10.3.2 Cases of Automatic Semicolon Insertion and “[no LineTerminator here]”
This section is non-normative.
ECMAScript contains grammar productions which include “[no
The rest of this section describes a number of productions using “[no
12.10.3.2.1 List of Grammar Productions with Optional Operands and “[no LineTerminator here]”
UpdateExpression .ContinueStatement .BreakStatement .ReturnStatement .YieldExpression .- Async Function Definitions (
15.8 ) with relation to Function Definitions (15.2 )
13 ECMAScript Language: Expressions
13.1 Identifiers
Syntax
yield and await are permitted as
let
await 0;13.1.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsStrict (this production) istrue and theStringValue ofIdentifier is either"arguments" or"eval" .
-
It is a Syntax Error if
IsStrict (this production) istrue .
-
It is a Syntax Error if the
goal symbol of the syntactic grammar isModule .
- It is a Syntax Error if this production has a [Yield] parameter.
- It is a Syntax Error if this production has an [Await] parameter.
-
It is a Syntax Error if this production has a [Yield] parameter and the
StringValue ofIdentifier is"yield" . -
It is a Syntax Error if this production has an [Await] parameter and the
StringValue ofIdentifier is"await" .
-
It is a Syntax Error if
IsStrict (this phrase) istrue and theStringValue ofIdentifierName is one of"implements" ,"interface" ,"let" ,"package" ,"private" ,"protected" ,"public" ,"static" , or"yield" . -
It is a Syntax Error if the
goal symbol of the syntactic grammar isModule and theStringValue ofIdentifierName is"await" . -
It is a Syntax Error if the
StringValue ofIdentifierName is theStringValue of anyReservedWord except foryieldorawait.
The
13.1.2 Static Semantics: StringValue
The
- Let idTextUnescaped be the
IdentifierCodePoints ofIdentifierName . - Return
CodePointsToString (idTextUnescaped).
- Return
"yield" .
- Return
"await" .
- Return the
StringValue ofIdentifierName .
- Return the
string-concatenation of 0x0023 (NUMBER SIGN) and theStringValue ofIdentifierName .
- Return the
SV ofStringLiteral .
13.1.3 Runtime Semantics: Evaluation
- Return ?
ResolveBinding (StringValue ofIdentifier ).
- Return ?
ResolveBinding ("yield" ).
- Return ?
ResolveBinding ("await" ).
The result of evaluating an
In yield may be used as an identifier. Evaluating the yield as if it was an
13.2 Primary Expression
Syntax
Supplemental Syntax
When processing an instance of the production
the interpretation of
13.2.1 The this Keyword
13.2.1.1 Runtime Semantics: Evaluation
- Return ?
ResolveThisBinding ().
13.2.2 Identifier Reference
See
13.2.3 Literals
Syntax
13.2.3.1 Runtime Semantics: Evaluation
- Return
null .
- If
BooleanLiteral is the tokenfalse, returnfalse . - If
BooleanLiteral is the tokentrue, returntrue .
- Return the
NumericValue ofNumericLiteral as defined in12.9.3 .
- Return the
SV ofStringLiteral as defined in12.9.4.2 .
13.2.4 Array Initializer
An
Array elements may be elided at the beginning, middle or end of the element list. Whenever a comma in the element list is not preceded by an
Syntax
13.2.4.1 Runtime Semantics: ArrayAccumulation
The
- Return ?
ArrayAccumulation ofElision with arguments array and (nextIndex + 1).
- If
Elision is present, then- Set nextIndex to ?
ArrayAccumulation ofElision with arguments array and nextIndex.
- Set nextIndex to ?
- Let initResult be ?
Evaluation ofAssignmentExpression . - Let initValue be ?
GetValue (initResult). - Perform !
CreateDataPropertyOrThrow (array, !ToString (𝔽 (nextIndex)), initValue). - Return nextIndex + 1.
- If
Elision is present, then- Set nextIndex to ?
ArrayAccumulation ofElision with arguments array and nextIndex.
- Set nextIndex to ?
- Return ?
ArrayAccumulation ofSpreadElement with arguments array and nextIndex.
- Set nextIndex to ?
ArrayAccumulation ofElementList with arguments array and nextIndex. - If
Elision is present, then- Set nextIndex to ?
ArrayAccumulation ofElision with arguments array and nextIndex.
- Set nextIndex to ?
- Let initResult be ?
Evaluation ofAssignmentExpression . - Let initValue be ?
GetValue (initResult). - Perform !
CreateDataPropertyOrThrow (array, !ToString (𝔽 (nextIndex)), initValue). - Return nextIndex + 1.
- Set nextIndex to ?
ArrayAccumulation ofElementList with arguments array and nextIndex. - If
Elision is present, then- Set nextIndex to ?
ArrayAccumulation ofElision with arguments array and nextIndex.
- Set nextIndex to ?
- Return ?
ArrayAccumulation ofSpreadElement with arguments array and nextIndex.
- Let spreadRef be ?
Evaluation ofAssignmentExpression . - Let spreadObj be ?
GetValue (spreadRef). - Let iteratorRecord be ?
GetIterator (spreadObj,sync ). - Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , return nextIndex. - Perform !
CreateDataPropertyOrThrow (array, !ToString (𝔽 (nextIndex)), next). - Set nextIndex to nextIndex + 1.
- Let next be ?
13.2.4.2 Runtime Semantics: Evaluation
- Let array be !
ArrayCreate (0). - If
Elision is present, then- Perform ?
ArrayAccumulation ofElision with arguments array and 0.
- Perform ?
- Return array.
- Let array be !
ArrayCreate (0). - Perform ?
ArrayAccumulation ofElementList with arguments array and 0. - Return array.
- Let array be !
ArrayCreate (0). - Let nextIndex be ?
ArrayAccumulation ofElementList with arguments array and 0. - If
Elision is present, then- Perform ?
ArrayAccumulation ofElision with arguments array and nextIndex.
- Perform ?
- Return array.
13.2.5 Object Initializer
An object initializer is an expression describing the initialization of an Object, written in a form resembling a literal. It is a list of zero or more pairs of
Syntax
In certain contexts,
13.2.5.1 Static Semantics: Early Errors
-
It is a Syntax Error if
HasDirectSuper ofMethodDefinition istrue . -
It is a Syntax Error if the
PrivateBoundIdentifiers ofMethodDefinition is not empty.
In addition to describing an actual object initializer the
- It is a Syntax Error if any source text is matched by this production.
This production exists so that
-
It is a Syntax Error if the
PropertyNameList ofPropertyDefinitionList contains any duplicate entries for"__proto__" and at least two of those entries were obtained from productions of the formPropertyDefinition : PropertyName : AssignmentExpression ObjectLiteral is contained within aScript that is being parsed forParseJSON (see step3 ofParseJSON ).
The
13.2.5.2 Static Semantics: IsComputedPropertyKey
The
- Return
false .
- Return
true .
13.2.5.3 Static Semantics: PropertyNameList
The
- Let propName be the
PropName ofPropertyDefinition . - If propName is
empty , return a new emptyList . - Return « propName ».
- Let list be the
PropertyNameList ofPropertyDefinitionList . - Let propName be the
PropName ofPropertyDefinition . - If propName is
empty , return list. - Return the
list-concatenation of list and « propName ».
13.2.5.4 Runtime Semantics: Evaluation
- Return
OrdinaryObjectCreate (%Object.prototype% ).
- Let obj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform ?
PropertyDefinitionEvaluation ofPropertyDefinitionList with argument obj. - Return obj.
- Return the
StringValue ofIdentifierName .
- Return the
SV ofStringLiteral .
- Let nbr be the
NumericValue ofNumericLiteral . - Return !
ToString (nbr).
- Let exprValue be ?
Evaluation ofAssignmentExpression . - Let propName be ?
GetValue (exprValue). - Return ?
ToPropertyKey (propName).
13.2.5.5 Runtime Semantics: PropertyDefinitionEvaluation
The
- Perform ?
PropertyDefinitionEvaluation ofPropertyDefinitionList with argument object. - Perform ?
PropertyDefinitionEvaluation ofPropertyDefinition with argument object. - Return
unused .
- Let exprValue be ?
Evaluation ofAssignmentExpression . - Let fromValue be ?
GetValue (exprValue). - Let excludedNames be a new empty
List . - Perform ?
CopyDataProperties (object, fromValue, excludedNames). - Return
unused .
- Let propName be the
StringValue ofIdentifierReference . - Let exprValue be ?
Evaluation ofIdentifierReference . - Let propValue be ?
GetValue (exprValue). Assert : object is an ordinary, extensible object with no non-configurable properties.- Perform !
CreateDataPropertyOrThrow (object, propName, propValue). - Return
unused .
- Let propKey be ?
Evaluation ofPropertyName . - If this
PropertyDefinition is contained within aScript that is being evaluated forParseJSON (see step6 ofParseJSON ), then- Let isProtoSetter be
false .
- Let isProtoSetter be
- Else if propKey is
"__proto__" andIsComputedPropertyKey ofPropertyName isfalse , then- Let isProtoSetter be
true .
- Let isProtoSetter be
- Else,
- Let isProtoSetter be
false .
- Let isProtoSetter be
- If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue and isProtoSetter isfalse , then- Let propValue be ?
NamedEvaluation ofAssignmentExpression with argument propKey.
- Let propValue be ?
- Else,
- Let exprValueRef be ?
Evaluation ofAssignmentExpression . - Let propValue be ?
GetValue (exprValueRef).
- Let exprValueRef be ?
- If isProtoSetter is
true , then- If propValue
is an Object or propValue isnull , then- Perform ! object.[[SetPrototypeOf]](propValue).
- Return
unused .
- If propValue
Assert : object is an ordinary, extensible object with no non-configurable properties.- Perform !
CreateDataPropertyOrThrow (object, propKey, propValue). - Return
unused .
- Perform ?
MethodDefinitionEvaluation ofMethodDefinition with arguments object andtrue . - Return
unused .
13.2.6 Function Defining Expressions
See
See
See
See
See
13.2.7 Regular Expression Literals
Syntax
See
13.2.7.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsValidRegularExpressionLiteral (RegularExpressionLiteral ) isfalse .
13.2.7.2 Static Semantics: IsValidRegularExpressionLiteral ( literal )
The abstract operation IsValidRegularExpressionLiteral takes argument literal (a
- Let flags be the
FlagText of literal. - If flags contains any code points other than
d,g,i,m,s,u,v, ory, or if flags contains any code point more than once, returnfalse . - If flags contains
u, let u betrue ; else let u befalse . - If flags contains
v, let v betrue ; else let v befalse . - Let patternText be the
BodyText of literal. - If u is
false and v isfalse , then- Let stringValue be
CodePointsToString (patternText). - Set patternText to the sequence of code points resulting from interpreting each of the 16-bit elements of stringValue as a Unicode BMP code point. UTF-16 decoding is not applied to the elements.
- Let stringValue be
- Let parseResult be
ParsePattern (patternText, u, v). - If parseResult is a
Parse Node , returntrue ; else returnfalse .
13.2.7.3 Runtime Semantics: Evaluation
- Let pattern be
CodePointsToString (BodyText ofRegularExpressionLiteral ). - Let flags be
CodePointsToString (FlagText ofRegularExpressionLiteral ). - Return !
RegExpCreate (pattern, flags).
13.2.8 Template Literals
Syntax
13.2.8.1 Static Semantics: Early Errors
-
It is a Syntax Error if the [Tagged] parameter was not set and
NoSubstitutionTemplate Contains NotEscapeSequence .
-
It is a Syntax Error if the number of elements in the
TemplateStrings ofTemplateLiteral with argumentfalse is greater than or equal to 232.
-
It is a Syntax Error if the [Tagged] parameter was not set and
TemplateHead Contains NotEscapeSequence .
-
It is a Syntax Error if the [Tagged] parameter was not set and
TemplateTail Contains NotEscapeSequence .
-
It is a Syntax Error if the [Tagged] parameter was not set and
TemplateMiddle Contains NotEscapeSequence .
13.2.8.2 Static Semantics: TemplateStrings
The
- Return «
TemplateString (NoSubstitutionTemplate , raw) ».
- Let head be «
TemplateString (TemplateHead , raw) ». - Let tail be the
TemplateStrings ofTemplateSpans with argument raw. - Return the
list-concatenation of head and tail.
- Return «
TemplateString (TemplateTail , raw) ».
- Let middle be the
TemplateStrings ofTemplateMiddleList with argument raw. - Let tail be «
TemplateString (TemplateTail , raw) ». - Return the
list-concatenation of middle and tail.
- Return «
TemplateString (TemplateMiddle , raw) ».
- Let front be the
TemplateStrings ofTemplateMiddleList with argument raw. - Let last be «
TemplateString (TemplateMiddle , raw) ». - Return the
list-concatenation of front and last.
13.2.8.3 Static Semantics: TemplateString ( templateToken, raw )
The abstract operation TemplateString takes arguments templateToken (a
This operation returns
13.2.8.4 GetTemplateObject ( templateLiteral )
The abstract operation GetTemplateObject takes argument templateLiteral (a
- Let realm be
the current Realm Record . - Let templateRegistry be realm.[[TemplateMap]].
- For each element e of templateRegistry, do
- If e.[[Site]] is
the same Parse Node as templateLiteral, then- Return e.[[Array]].
- If e.[[Site]] is
- Let rawStrings be the
TemplateStrings of templateLiteral with argumenttrue . Assert : rawStrings is aList of Strings.- Let cookedStrings be the
TemplateStrings of templateLiteral with argumentfalse . - Let count be the number of elements in the
List cookedStrings. Assert : count ≤ 232 - 1.- Let template be !
ArrayCreate (count). - Let rawObj be !
ArrayCreate (count). - Let index be 0.
- Repeat, while index < count,
- Let prop be !
ToString (𝔽 (index)). - Let cookedValue be cookedStrings[index].
- Perform !
DefinePropertyOrThrow (template, prop, PropertyDescriptor { [[Value]]: cookedValue, [[Writable]]:false , [[Enumerable]]:true , [[Configurable]]:false }). - Let rawValue be the String value rawStrings[index].
- Perform !
DefinePropertyOrThrow (rawObj, prop, PropertyDescriptor { [[Value]]: rawValue, [[Writable]]:false , [[Enumerable]]:true , [[Configurable]]:false }). - Set index to index + 1.
- Let prop be !
- Perform !
SetIntegrityLevel (rawObj,frozen ). - Perform !
DefinePropertyOrThrow (template,"raw" , PropertyDescriptor { [[Value]]: rawObj, [[Writable]]:false , [[Enumerable]]:false , [[Configurable]]:false }). - Perform !
SetIntegrityLevel (template,frozen ). - Append the
Record { [[Site]]: templateLiteral, [[Array]]: template } to realm.[[TemplateMap]]. - Return template.
The creation of a template object cannot result in an
Each
Future editions of this specification may define additional non-enumerable properties of template objects.
13.2.8.5 Runtime Semantics: SubstitutionEvaluation
The
- Return a new empty
List .
- Return ?
SubstitutionEvaluation ofTemplateMiddleList .
- Let subRef be ?
Evaluation ofExpression . - Let sub be ?
GetValue (subRef). - Return « sub ».
- Let preceding be ?
SubstitutionEvaluation ofTemplateMiddleList . - Let nextRef be ?
Evaluation ofExpression . - Let next be ?
GetValue (nextRef). - Return the
list-concatenation of preceding and « next ».
13.2.8.6 Runtime Semantics: Evaluation
- Return the
TV ofNoSubstitutionTemplate as defined in12.9.6 .
- Let head be the
TV ofTemplateHead as defined in12.9.6 . - Let subRef be ?
Evaluation ofExpression . - Let sub be ?
GetValue (subRef). - Let middle be ?
ToString (sub). - Let tail be ?
Evaluation ofTemplateSpans . - Return the
string-concatenation of head, middle, and tail.
The string conversion semantics applied to the String.prototype.concat rather than the + operator.
- Return the
TV ofTemplateTail as defined in12.9.6 .
- Let head be ?
Evaluation ofTemplateMiddleList . - Let tail be the
TV ofTemplateTail as defined in12.9.6 . - Return the
string-concatenation of head and tail.
- Let head be the
TV ofTemplateMiddle as defined in12.9.6 . - Let subRef be ?
Evaluation ofExpression . - Let sub be ?
GetValue (subRef). - Let middle be ?
ToString (sub). - Return the
string-concatenation of head and middle.
The string conversion semantics applied to the String.prototype.concat rather than the + operator.
- Let rest be ?
Evaluation ofTemplateMiddleList . - Let middle be the
TV ofTemplateMiddle as defined in12.9.6 . - Let subRef be ?
Evaluation ofExpression . - Let sub be ?
GetValue (subRef). - Let last be ?
ToString (sub). - Return the
string-concatenation of rest, middle, and last.
The string conversion semantics applied to the String.prototype.concat rather than the + operator.
13.2.9 The Grouping Operator
13.2.9.1 Static Semantics: Early Errors
13.2.9.2 Runtime Semantics: Evaluation
- Let expr be the
ParenthesizedExpression that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return ?
Evaluation of expr.
- Return ?
Evaluation ofExpression . This may be of type Reference.
This algorithm does not apply delete and typeof may be applied to parenthesized expressions.
13.3 Left-Hand-Side Expressions
Syntax
Supplemental Syntax
When processing an instance of the production
the interpretation of
13.3.1 Static Semantics
13.3.1.1 Static Semantics: Early Errors
- It is a Syntax Error if any source text is matched by this production.
This production exists in order to prevent automatic semicolon insertion rules (
a?.b
`c`so that it would be interpreted as two valid statements. The purpose is to maintain consistency with similar code without optional chaining:
a.b
`c`which is a valid statement and where automatic semicolon insertion does not apply.
-
It is a Syntax Error if the syntactic
goal symbol is notModule .
13.3.2 Property Accessors
Properties are accessed by name, using either the dot notation:
or the bracket notation:
The dot notation is explained by the following syntactic conversion:
is identical in its behaviour to
and similarly
is identical in its behaviour to
where <identifier-name-string> is the
13.3.2.1 Runtime Semantics: Evaluation
- Let baseReference be ?
Evaluation ofMemberExpression . - Let baseValue be ?
GetValue (baseReference). - Let strict be
IsStrict (thisMemberExpression ). - Return ?
EvaluatePropertyAccessWithExpressionKey (baseValue,Expression , strict).
- Let baseReference be ?
Evaluation ofMemberExpression . - Let baseValue be ?
GetValue (baseReference). - Let strict be
IsStrict (thisMemberExpression ). - Return
EvaluatePropertyAccessWithIdentifierKey (baseValue,IdentifierName , strict).
- Let baseReference be ?
Evaluation ofMemberExpression . - Let baseValue be ?
GetValue (baseReference). - Let fieldNameString be the
StringValue ofPrivateIdentifier . - Return
MakePrivateReference (baseValue, fieldNameString).
- Let baseReference be ?
Evaluation ofCallExpression . - Let baseValue be ?
GetValue (baseReference). - Let strict be
IsStrict (thisCallExpression ). - Return ?
EvaluatePropertyAccessWithExpressionKey (baseValue,Expression , strict).
- Let baseReference be ?
Evaluation ofCallExpression . - Let baseValue be ?
GetValue (baseReference). - Let strict be
IsStrict (thisCallExpression ). - Return
EvaluatePropertyAccessWithIdentifierKey (baseValue,IdentifierName , strict).
- Let baseReference be ?
Evaluation ofCallExpression . - Let baseValue be ?
GetValue (baseReference). - Let fieldNameString be the
StringValue ofPrivateIdentifier . - Return
MakePrivateReference (baseValue, fieldNameString).
13.3.3 EvaluatePropertyAccessWithExpressionKey ( baseValue, expression, strict )
The abstract operation EvaluatePropertyAccessWithExpressionKey takes arguments baseValue (an
- Let propertyNameReference be ?
Evaluation of expression. - Let propertyNameValue be ?
GetValue (propertyNameReference). - NOTE: In most cases,
ToPropertyKey will be performed on propertyNameValue immediately after this step. However, in the case ofa[b] = c, it will not be performed until after evaluation ofc. - Return the
Reference Record { [[Base]]: baseValue, [[ReferencedName]]: propertyNameValue, [[Strict]]: strict, [[ThisValue]]:empty }.
13.3.4 EvaluatePropertyAccessWithIdentifierKey ( baseValue, identifierName, strict )
The abstract operation EvaluatePropertyAccessWithIdentifierKey takes arguments baseValue (an
- Let propertyNameString be the
StringValue of identifierName. - Return the
Reference Record { [[Base]]: baseValue, [[ReferencedName]]: propertyNameString, [[Strict]]: strict, [[ThisValue]]:empty }.
13.3.5 The new Operator
13.3.5.1 Runtime Semantics: Evaluation
- Return ?
EvaluateNew (NewExpression ,empty ).
- Return ?
EvaluateNew (MemberExpression ,Arguments ).
13.3.5.1.1 EvaluateNew ( constructExpr, arguments )
The abstract operation EvaluateNew takes arguments constructExpr (a
- Let ref be ?
Evaluation of constructExpr. - Let constructor be ?
GetValue (ref). - If arguments is
empty , then- Let argList be a new empty
List .
- Let argList be a new empty
- Else,
- Let argList be ?
ArgumentListEvaluation of arguments.
- Let argList be ?
- If
IsConstructor (constructor) isfalse , throw aTypeError exception. - Return ?
Construct (constructor, argList).
13.3.6 Function Calls
13.3.6.1 Runtime Semantics: Evaluation
- Let expr be the
CallMemberExpression that iscovered byCoverCallExpressionAndAsyncArrowHead . - Let memberExpr be the
MemberExpression of expr. - Let arguments be the
Arguments of expr. - Let ref be ?
Evaluation of memberExpr. - Let func be ?
GetValue (ref). - If ref is a
Reference Record ,IsPropertyReference (ref) isfalse , and ref.[[ReferencedName]] is"eval" , then- If
SameValue (func,%eval% ) istrue , then- Let argList be ?
ArgumentListEvaluation of arguments. - If argList has no elements, return
undefined . - Let evalArg be the first element of argList.
- If
IsStrict (thisCallExpression ) istrue , let strictCaller betrue . Otherwise let strictCaller befalse . - Return ?
PerformEval (evalArg, strictCaller,true ).
- Let argList be ?
- If
- Let thisCall be this
CallExpression . - Let tailCall be
IsInTailPosition (thisCall). - Return ?
EvaluateCall (func, ref, arguments, tailCall).
A
- Let ref be ?
Evaluation ofCallExpression . - Let func be ?
GetValue (ref). - Let thisCall be this
CallExpression . - Let tailCall be
IsInTailPosition (thisCall). - Return ?
EvaluateCall (func, ref,Arguments , tailCall).
13.3.6.2 EvaluateCall ( func, ref, arguments, tailPosition )
The abstract operation EvaluateCall takes arguments func (an
- If ref is a
Reference Record , then- If
IsPropertyReference (ref) istrue , then- Let thisValue be
GetThisValue (ref).
- Let thisValue be
- Else,
- Let refEnv be ref.[[Base]].
Assert : refEnv is anEnvironment Record .- Let thisValue be refEnv.WithBaseObject().
- If
- Else,
- Let thisValue be
undefined .
- Let thisValue be
- Let argList be ?
ArgumentListEvaluation of arguments. - If func
is not an Object , throw aTypeError exception. - If
IsCallable (func) isfalse , throw aTypeError exception. - If tailPosition is
true , performPrepareForTailCall (). - Return ?
Call (func, thisValue, argList).
13.3.7 The super Keyword
13.3.7.1 Runtime Semantics: Evaluation
- Let env be
GetThisEnvironment (). - Let actualThis be ? env.GetThisBinding().
- Let propertyNameReference be ?
Evaluation ofExpression . - Let propertyNameValue be ?
GetValue (propertyNameReference). - Let strict be
IsStrict (thisSuperProperty ). - NOTE: In most cases,
ToPropertyKey will be performed on propertyNameValue immediately after this step. However, in the case ofsuper[b] = c, it will not be performed until after evaluation ofc. - Return
MakeSuperPropertyReference (actualThis, propertyNameValue, strict).
- Let env be
GetThisEnvironment (). - Let actualThis be ? env.GetThisBinding().
- Let propertyKey be the
StringValue ofIdentifierName . - Let strict be
IsStrict (thisSuperProperty ). - Return
MakeSuperPropertyReference (actualThis, propertyKey, strict).
- Let newTarget be
GetNewTarget (). Assert : newTarget is aconstructor .- Let func be
GetSuperConstructor (). - Let argList be ?
ArgumentListEvaluation ofArguments . - If
IsConstructor (func) isfalse , throw aTypeError exception. - Let result be ?
Construct (func, argList, newTarget). - Let thisER be
GetThisEnvironment (). Assert : thisER is aFunction Environment Record .- Perform ?
BindThisValue (thisER, result). - Let F be thisER.[[FunctionObject]].
Assert : F is an ECMAScriptfunction object .- Perform ?
InitializeInstanceElements (result, F). - Return result.
13.3.7.2 GetSuperConstructor ( )
The abstract operation GetSuperConstructor takes no arguments and returns an
- Let envRec be
GetThisEnvironment (). Assert : envRec is aFunction Environment Record .- Let activeFunction be envRec.[[FunctionObject]].
Assert : activeFunction is an ECMAScriptfunction object .- Let superConstructor be ! activeFunction.[[GetPrototypeOf]]().
- Return superConstructor.
13.3.7.3 MakeSuperPropertyReference ( actualThis, propertyKey, strict )
The abstract operation MakeSuperPropertyReference takes arguments actualThis (an
- Let env be
GetThisEnvironment (). Assert : env.HasSuperBinding() istrue .Assert : env is aFunction Environment Record .- Let baseValue be
GetSuperBase (env). - Return the
Reference Record { [[Base]]: baseValue, [[ReferencedName]]: propertyKey, [[Strict]]: strict, [[ThisValue]]: actualThis }.
13.3.8 Argument Lists
The evaluation of an argument list produces a
13.3.8.1 Runtime Semantics: ArgumentListEvaluation
The
- Return a new empty
List .
- Let ref be ?
Evaluation ofAssignmentExpression . - Let arg be ?
GetValue (ref). - Return « arg ».
- Let list be a new empty
List . - Let spreadRef be ?
Evaluation ofAssignmentExpression . - Let spreadObj be ?
GetValue (spreadRef). - Let iteratorRecord be ?
GetIterator (spreadObj,sync ). - Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , return list. - Append next to list.
- Let next be ?
- Let precedingArgs be ?
ArgumentListEvaluation ofArgumentList . - Let ref be ?
Evaluation ofAssignmentExpression . - Let arg be ?
GetValue (ref). - Return the
list-concatenation of precedingArgs and « arg ».
- Let precedingArgs be ?
ArgumentListEvaluation ofArgumentList . - Let spreadRef be ?
Evaluation ofAssignmentExpression . - Let iteratorRecord be ?
GetIterator (?GetValue (spreadRef),sync ). - Repeat,
- Let next be ?
IteratorStepValue (iteratorRecord). - If next is
done , return precedingArgs. - Append next to precedingArgs.
- Let next be ?
- Let templateLiteral be this
TemplateLiteral . - Let siteObj be
GetTemplateObject (templateLiteral). - Return « siteObj ».
- Let templateLiteral be this
TemplateLiteral . - Let siteObj be
GetTemplateObject (templateLiteral). - Let remaining be ?
ArgumentListEvaluation ofSubstitutionTemplate . - Return the
list-concatenation of « siteObj » and remaining.
- Let firstSubRef be ?
Evaluation ofExpression . - Let firstSub be ?
GetValue (firstSubRef). - Let restSub be ?
SubstitutionEvaluation ofTemplateSpans . Assert : restSub is a possibly emptyList .- Return the
list-concatenation of « firstSub » and restSub.
13.3.9 Optional Chains
?..13.3.9.1 Runtime Semantics: Evaluation
- Let baseReference be ?
Evaluation ofMemberExpression . - Let baseValue be ?
GetValue (baseReference). - If baseValue is either
undefined ornull , then- Return
undefined .
- Return
- Return ?
ChainEvaluation ofOptionalChain with arguments baseValue and baseReference.
- Let baseReference be ?
Evaluation ofCallExpression . - Let baseValue be ?
GetValue (baseReference). - If baseValue is either
undefined ornull , then- Return
undefined .
- Return
- Return ?
ChainEvaluation ofOptionalChain with arguments baseValue and baseReference.
- Let baseReference be ?
Evaluation ofOptionalExpression . - Let baseValue be ?
GetValue (baseReference). - If baseValue is either
undefined ornull , then- Return
undefined .
- Return
- Return ?
ChainEvaluation ofOptionalChain with arguments baseValue and baseReference.
13.3.9.2 Runtime Semantics: ChainEvaluation
The
- Let thisChain be this
OptionalChain . - Let tailCall be
IsInTailPosition (thisChain). - Return ?
EvaluateCall (baseValue, baseReference,Arguments , tailCall).
- Let strict be
IsStrict (thisOptionalChain ). - Return ?
EvaluatePropertyAccessWithExpressionKey (baseValue,Expression , strict).
- Let strict be
IsStrict (thisOptionalChain ). - Return
EvaluatePropertyAccessWithIdentifierKey (baseValue,IdentifierName , strict).
- Let fieldNameString be the
StringValue ofPrivateIdentifier . - Return
MakePrivateReference (baseValue, fieldNameString).
- Let optionalChain be
OptionalChain . - Let newReference be ?
ChainEvaluation of optionalChain with arguments baseValue and baseReference. - Let newValue be ?
GetValue (newReference). - Let thisChain be this
OptionalChain . - Let tailCall be
IsInTailPosition (thisChain). - Return ?
EvaluateCall (newValue, newReference,Arguments , tailCall).
- Let optionalChain be
OptionalChain . - Let newReference be ?
ChainEvaluation of optionalChain with arguments baseValue and baseReference. - Let newValue be ?
GetValue (newReference). - Let strict be
IsStrict (thisOptionalChain ). - Return ?
EvaluatePropertyAccessWithExpressionKey (newValue,Expression , strict).
- Let optionalChain be
OptionalChain . - Let newReference be ?
ChainEvaluation of optionalChain with arguments baseValue and baseReference. - Let newValue be ?
GetValue (newReference). - Let strict be
IsStrict (thisOptionalChain ). - Return
EvaluatePropertyAccessWithIdentifierKey (newValue,IdentifierName , strict).
- Let optionalChain be
OptionalChain . - Let newReference be ?
ChainEvaluation of optionalChain with arguments baseValue and baseReference. - Let newValue be ?
GetValue (newReference). - Let fieldNameString be the
StringValue ofPrivateIdentifier . - Return
MakePrivateReference (newValue, fieldNameString).
13.3.10 Import Calls
13.3.10.1 Runtime Semantics: Evaluation
- Return ?
EvaluateImportCall (AssignmentExpression ).
- Return ?
EvaluateImportCall (the firstAssignmentExpression , the secondAssignmentExpression ).
13.3.10.2 EvaluateImportCall ( specifierExpression [ , optionsExpression ] )
The abstract operation EvaluateImportCall takes argument specifierExpression (a
- Let referrer be
GetActiveScriptOrModule (). - If referrer is
null , set referrer tothe current Realm Record . - Let specifierRef be ?
Evaluation of specifierExpression. - Let specifier be ?
GetValue (specifierRef). - If optionsExpression is present, then
- Let optionsRef be ?
Evaluation of optionsExpression. - Let options be ?
GetValue (optionsRef).
- Let optionsRef be ?
- Else,
- Let options be
undefined .
- Let options be
- Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let specifierString be
Completion (ToString (specifier)). IfAbruptRejectPromise (specifierString, promiseCapability).- Let attributes be a new empty
List . - If options is not
undefined , then- If options
is not an Object , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « a newly createdTypeError object »). - Return promiseCapability.[[Promise]].
- Perform !
- Let attributesObj be
Completion (Get (options,"with" )). IfAbruptRejectPromise (attributesObj, promiseCapability).- If attributesObj is not
undefined , then- If attributesObj
is not an Object , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « a newly createdTypeError object »). - Return promiseCapability.[[Promise]].
- Perform !
- Let entries be
Completion (EnumerableOwnProperties (attributesObj,key+value )). IfAbruptRejectPromise (entries, promiseCapability).- For each element entry of entries, do
- Let key be !
Get (entry,"0" ). - Let value be !
Get (entry,"1" ). - If key
is a String , then- If value
is not a String , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « a newly createdTypeError object »). - Return promiseCapability.[[Promise]].
- Perform !
- Append the
ImportAttribute Record { [[Key]]: key, [[Value]]: value } to attributes.
- If value
- Let key be !
- If attributesObj
- If
AllImportAttributesSupported (attributes) isfalse , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « a newly createdTypeError object »). - Return promiseCapability.[[Promise]].
- Perform !
- Sort attributes according to the lexicographic order of their [[Key]] field, treating the value of each such field as a sequence of UTF-16 code unit values. NOTE: This sorting is observable only in that
hosts are prohibited from changing behaviour based on the order in which attributes are enumerated.
- If options
- Let moduleRequest be a new
ModuleRequest Record { [[Specifier]]: specifierString, [[Attributes]]: attributes }. - Perform
HostLoadImportedModule (referrer, moduleRequest,empty , promiseCapability). - Return promiseCapability.[[Promise]].
13.3.10.3 ContinueDynamicImport ( promiseCapability, moduleCompletion )
The abstract operation ContinueDynamicImport takes arguments promiseCapability (a import()
- If moduleCompletion is an
abrupt completion , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « moduleCompletion.[[Value]] »). - Return
unused .
- Perform !
- Let module be moduleCompletion.[[Value]].
- Let loadPromise be module.LoadRequestedModules().
- Let rejectedClosure be a new
Abstract Closure with parameters (reason) that captures promiseCapability and performs the following steps when called:- Perform !
Call (promiseCapability.[[Reject]],undefined , « reason »). - Return
unused .
- Perform !
- Let onRejected be
CreateBuiltinFunction (rejectedClosure, 1,"" , « »). - Let linkAndEvaluateClosure be a new
Abstract Closure with no parameters that captures module, promiseCapability, and onRejected and performs the following steps when called:- Let link be
Completion (module.Link()). - If link is an
abrupt completion , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « link.[[Value]] »). - Return
unused .
- Perform !
- Let evaluatePromise be module.Evaluate().
- Let fulfilledClosure be a new
Abstract Closure with no parameters that captures module and promiseCapability and performs the following steps when called:- Let namespace be
GetModuleNamespace (module). - Perform ! Call(promiseCapability.[[Resolve]],
undefined , « namespace »). - Return
unused .
- Let namespace be
- Let onFulfilled be
CreateBuiltinFunction (fulfilledClosure, 0,"" , « »). - Perform
PerformPromiseThen (evaluatePromise, onFulfilled, onRejected). - Return
unused .
- Let link be
- Let linkAndEvaluate be
CreateBuiltinFunction (linkAndEvaluateClosure, 0,"" , « »). - Perform
PerformPromiseThen (loadPromise, linkAndEvaluate, onRejected). - Return
unused .
13.3.11 Tagged Templates
A tagged template is a function call where the arguments of the call are derived from a
13.3.11.1 Runtime Semantics: Evaluation
- Let tagRef be ?
Evaluation ofMemberExpression . - Let tagFunc be ?
GetValue (tagRef). - Let thisCall be this
MemberExpression . - Let tailCall be
IsInTailPosition (thisCall). - Return ?
EvaluateCall (tagFunc, tagRef,TemplateLiteral , tailCall).
- Let tagRef be ?
Evaluation ofCallExpression . - Let tagFunc be ?
GetValue (tagRef). - Let thisCall be this
CallExpression . - Let tailCall be
IsInTailPosition (thisCall). - Return ?
EvaluateCall (tagFunc, tagRef,TemplateLiteral , tailCall).
13.3.12 Meta Properties
13.3.12.1 Runtime Semantics: Evaluation
- Return
GetNewTarget ().
- Let module be
GetActiveScriptOrModule (). Assert : module is aSource Text Module Record .- Let importMeta be module.[[ImportMeta]].
- If importMeta is
empty , then- Set importMeta to
OrdinaryObjectCreate (null ). - Let importMetaValues be
HostGetImportMetaProperties (module). - For each
Record { [[Key]], [[Value]] } p of importMetaValues, do- Perform !
CreateDataPropertyOrThrow (importMeta, p.[[Key]], p.[[Value]]).
- Perform !
- Perform
HostFinalizeImportMeta (importMeta, module). - Set module.[[ImportMeta]] to importMeta.
- Return importMeta.
- Set importMeta to
- Else,
Assert : importMetais an Object .- Return importMeta.
13.3.12.1.1 HostGetImportMetaProperties ( moduleRecord )
The import.meta.
The default implementation of HostGetImportMetaProperties is to return a new empty
13.3.12.1.2 HostFinalizeImportMeta ( importMeta, moduleRecord )
The import.meta.
Most
The default implementation of HostFinalizeImportMeta is to return
13.4 Update Expressions
Syntax
13.4.1 Static Semantics: Early Errors
-
It is an early Syntax Error if the
AssignmentTargetType ofLeftHandSideExpression is notsimple .
-
It is an early Syntax Error if the
AssignmentTargetType ofUnaryExpression is notsimple .
13.4.2 Postfix Increment Operator
13.4.2.1 Runtime Semantics: Evaluation
- Let lhs be ?
Evaluation ofLeftHandSideExpression . - Let oldValue be ?
ToNumeric (?GetValue (lhs)). - If oldValue
is a Number , then- Let newValue be
Number::add (oldValue,1 𝔽).
- Let newValue be
- Else,
Assert : oldValueis a BigInt .- Let newValue be
BigInt::add (oldValue,1 ℤ).
- Perform ?
PutValue (lhs, newValue). - Return oldValue.
13.4.3 Postfix Decrement Operator
13.4.3.1 Runtime Semantics: Evaluation
- Let lhs be ?
Evaluation ofLeftHandSideExpression . - Let oldValue be ?
ToNumeric (?GetValue (lhs)). - If oldValue
is a Number , then- Let newValue be
Number::subtract (oldValue,1 𝔽).
- Let newValue be
- Else,
Assert : oldValueis a BigInt .- Let newValue be
BigInt::subtract (oldValue,1 ℤ).
- Perform ?
PutValue (lhs, newValue). - Return oldValue.
13.4.4 Prefix Increment Operator
13.4.4.1 Runtime Semantics: Evaluation
- Let expr be ?
Evaluation ofUnaryExpression . - Let oldValue be ?
ToNumeric (?GetValue (expr)). - If oldValue
is a Number , then- Let newValue be
Number::add (oldValue,1 𝔽).
- Let newValue be
- Else,
Assert : oldValueis a BigInt .- Let newValue be
BigInt::add (oldValue,1 ℤ).
- Perform ?
PutValue (expr, newValue). - Return newValue.
13.4.5 Prefix Decrement Operator
13.4.5.1 Runtime Semantics: Evaluation
- Let expr be ?
Evaluation ofUnaryExpression . - Let oldValue be ?
ToNumeric (?GetValue (expr)). - If oldValue
is a Number , then- Let newValue be
Number::subtract (oldValue,1 𝔽).
- Let newValue be
- Else,
Assert : oldValueis a BigInt .- Let newValue be
BigInt::subtract (oldValue,1 ℤ).
- Perform ?
PutValue (expr, newValue). - Return newValue.
13.5 Unary Operators
Syntax
13.5.1 The delete Operator
13.5.1.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsStrict (theUnaryExpression ) istrue and the derivedUnaryExpression isPrimaryExpression : IdentifierReference MemberExpression : MemberExpression . PrivateIdentifier CallExpression : CallExpression . PrivateIdentifier OptionalChain : ?. PrivateIdentifier OptionalChain : OptionalChain . PrivateIdentifier -
It is a Syntax Error if the derived
UnaryExpression is
PrimaryExpression : CoverParenthesizedExpressionAndArrowParameterList
andCoverParenthesizedExpressionAndArrowParameterList ultimately derives a phrase that, if used in place ofUnaryExpression , would produce a Syntax Error according to these rules. This rule is recursively applied.
The last rule means that expressions such as delete (((foo))) produce
13.5.1.2 Runtime Semantics: Evaluation
- Let ref be ?
Evaluation ofUnaryExpression . - If ref is not a
Reference Record , returntrue . - If
IsUnresolvableReference (ref) istrue , thenAssert : ref.[[Strict]] isfalse .- Return
true .
- If
IsPropertyReference (ref) istrue , thenAssert :IsPrivateReference (ref) isfalse .- If
IsSuperReference (ref) istrue , throw aReferenceError exception. - Let baseObj be ?
ToObject (ref.[[Base]]). - If ref.[[ReferencedName]] is not a
property key , then- Set ref.[[ReferencedName]] to ?
ToPropertyKey (ref.[[ReferencedName]]).
- Set ref.[[ReferencedName]] to ?
- Let deleteStatus be ? baseObj.[[Delete]](ref.[[ReferencedName]]).
- If deleteStatus is
false and ref.[[Strict]] istrue , throw aTypeError exception. - Return deleteStatus.
- Else,
- Let base be ref.[[Base]].
Assert : base is anEnvironment Record .- Return ? base.DeleteBinding(ref.[[ReferencedName]]).
When a delete operator occurs within delete operator occurs within
The object that may be created in step
13.5.2 The void Operator
13.5.2.1 Runtime Semantics: Evaluation
- Let expr be ?
Evaluation ofUnaryExpression . - Perform ?
GetValue (expr). - Return
undefined .
13.5.3 The typeof Operator
13.5.3.1 Runtime Semantics: Evaluation
- Let val be ?
Evaluation ofUnaryExpression . - If val is a
Reference Record , then- If
IsUnresolvableReference (val) istrue , return"undefined" .
- If
- Set val to ?
GetValue (val). - If val is
undefined , return"undefined" . - If val is
null , return"object" . - If val
is a String , return"string" . - If val
is a Symbol , return"symbol" . - If val
is a Boolean , return"boolean" . - If val
is a Number , return"number" . - If val
is a BigInt , return"bigint" . Assert : valis an Object .- NOTE: This step is replaced in section
B.3.6.3 . - If val has a [[Call]] internal slot, return
"function" . - Return
"object" .
13.5.4 Unary + Operator
The unary + operator converts its operand to
13.5.4.1 Runtime Semantics: Evaluation
- Let expr be ?
Evaluation ofUnaryExpression . - Return ?
ToNumber (?GetValue (expr)).
13.5.5 Unary - Operator
The unary - operator converts its operand to a numeric value and then negates it. Negating
13.5.5.1 Runtime Semantics: Evaluation
- Let expr be ?
Evaluation ofUnaryExpression . - Let oldValue be ?
ToNumeric (?GetValue (expr)). - If oldValue
is a Number , then- Return
Number::unaryMinus (oldValue).
- Return
- Else,
Assert : oldValueis a BigInt .- Return
BigInt::unaryMinus (oldValue).
13.5.6 Bitwise NOT Operator ( ~ )
13.5.6.1 Runtime Semantics: Evaluation
- Let expr be ?
Evaluation ofUnaryExpression . - Let oldValue be ?
ToNumeric (?GetValue (expr)). - If oldValue
is a Number , then- Return
Number::bitwiseNOT (oldValue).
- Return
- Else,
Assert : oldValueis a BigInt .- Return
BigInt::bitwiseNOT (oldValue).
13.5.7 Logical NOT Operator ( ! )
13.5.7.1 Runtime Semantics: Evaluation
- Let expr be ?
Evaluation ofUnaryExpression . - Let oldValue be
ToBoolean (?GetValue (expr)). - If oldValue is
true , returnfalse . - Return
true .
13.6 Exponentiation Operator
Syntax
13.6.1 Runtime Semantics: Evaluation
13.7 Multiplicative Operators
Syntax
- The
*operator performs multiplication, producing the product of its operands. - The
/operator performs division, producing the quotient of its operands. - The
%operator yields the remainder of its operands from an implied division.
13.7.1 Runtime Semantics: Evaluation
- Let opText be the
source text matched by MultiplicativeOperator . - Return ?
EvaluateStringOrNumericBinaryExpression (MultiplicativeExpression , opText,ExponentiationExpression ).
13.8 Additive Operators
Syntax
13.8.1 The Addition Operator ( + )
The addition operator either performs string concatenation or numeric addition.
13.8.1.1 Runtime Semantics: Evaluation
13.8.2 The Subtraction Operator ( - )
The - operator performs subtraction, producing the difference of its operands.
13.8.2.1 Runtime Semantics: Evaluation
13.9 Bitwise Shift Operators
Syntax
13.9.1 The Left Shift Operator ( << )
Performs a bitwise left shift operation on the left operand by the amount specified by the right operand.
13.9.1.1 Runtime Semantics: Evaluation
- Return ?
EvaluateStringOrNumericBinaryExpression (ShiftExpression ,<<,AdditiveExpression ).
13.9.2 The Signed Right Shift Operator ( >> )
Performs a sign-filling bitwise right shift operation on the left operand by the amount specified by the right operand.
13.9.2.1 Runtime Semantics: Evaluation
- Return ?
EvaluateStringOrNumericBinaryExpression (ShiftExpression ,>>,AdditiveExpression ).
13.9.3 The Unsigned Right Shift Operator ( >>> )
Performs a zero-filling bitwise right shift operation on the left operand by the amount specified by the right operand.
13.9.3.1 Runtime Semantics: Evaluation
- Return ?
EvaluateStringOrNumericBinaryExpression (ShiftExpression ,>>>,AdditiveExpression ).
13.10 Relational Operators
The result of evaluating a relational operator is always of type Boolean, reflecting whether the relationship named by the operator holds between its two operands.
Syntax
The [In] grammar parameter is needed to avoid confusing the in operator in a relational expression with the in operator in a for statement.
13.10.1 Runtime Semantics: Evaluation
- Let lRef be ?
Evaluation ofRelationalExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofShiftExpression . - Let rVal be ?
GetValue (rRef). - Let r be ?
IsLessThan (lVal, rVal,true ). - If r is
undefined , returnfalse . Otherwise, return r.
- Let lRef be ?
Evaluation ofRelationalExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofShiftExpression . - Let rVal be ?
GetValue (rRef). - Let r be ?
IsLessThan (rVal, lVal,false ). - If r is
undefined , returnfalse . Otherwise, return r.
- Let lRef be ?
Evaluation ofRelationalExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofShiftExpression . - Let rVal be ?
GetValue (rRef). - Let r be ?
IsLessThan (rVal, lVal,false ). - If r is either
true orundefined , returnfalse . Otherwise, returntrue .
- Let lRef be ?
Evaluation ofRelationalExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofShiftExpression . - Let rVal be ?
GetValue (rRef). - Let r be ?
IsLessThan (lVal, rVal,true ). - If r is either
true orundefined , returnfalse . Otherwise, returntrue .
- Let lRef be ?
Evaluation ofRelationalExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofShiftExpression . - Let rVal be ?
GetValue (rRef). - Return ?
InstanceofOperator (lVal, rVal).
- Let lRef be ?
Evaluation ofRelationalExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofShiftExpression . - Let rVal be ?
GetValue (rRef). - If rVal
is not an Object , throw aTypeError exception. - Return ?
HasProperty (rVal, ?ToPropertyKey (lVal)).
- Let privateIdentifier be the
StringValue ofPrivateIdentifier . - Let rRef be ?
Evaluation ofShiftExpression . - Let rVal be ?
GetValue (rRef). - If rVal
is not an Object , throw aTypeError exception. - Let privateEnv be the
running execution context 's PrivateEnvironment. Assert : privateEnv is notnull .- Let privateName be
ResolvePrivateIdentifier (privateEnv, privateIdentifier). - If
PrivateElementFind (rVal, privateName) is notempty , returntrue . - Return
false .
13.10.2 InstanceofOperator ( V, target )
The abstract operation InstanceofOperator takes arguments V (an
- If target
is not an Object , throw aTypeError exception. - Let instOfHandler be ?
GetMethod (target,%Symbol.hasInstance% ). - If instOfHandler is not
undefined , then - If
IsCallable (target) isfalse , throw aTypeError exception. - Return ?
OrdinaryHasInstance (target, V).
Steps instanceof operator semantics. If an object does not define or inherit instanceof semantics.
13.11 Equality Operators
The result of evaluating an equality operator is always of type Boolean, reflecting whether the relationship named by the operator holds between its two operands.
Syntax
13.11.1 Runtime Semantics: Evaluation
- Let lRef be ?
Evaluation ofEqualityExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofRelationalExpression . - Let rVal be ?
GetValue (rRef). - Return ?
IsLooselyEqual (rVal, lVal).
- Let lRef be ?
Evaluation ofEqualityExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofRelationalExpression . - Let rVal be ?
GetValue (rRef). - Let r be ?
IsLooselyEqual (rVal, lVal). - If r is
true , returnfalse . Otherwise, returntrue .
- Let lRef be ?
Evaluation ofEqualityExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofRelationalExpression . - Let rVal be ?
GetValue (rRef). - Return
IsStrictlyEqual (rVal, lVal).
- Let lRef be ?
Evaluation ofEqualityExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofRelationalExpression . - Let rVal be ?
GetValue (rRef). - Let r be
IsStrictlyEqual (rVal, lVal). - If r is
true , returnfalse . Otherwise, returntrue .
Given the above definition of equality:
-
String comparison can be forced by:
`${a}` == `${b}`. -
Numeric comparison can be forced by:
+a == +b. -
Boolean comparison can be forced by:
!a == !b.
The equality operators maintain the following invariants:
-
A != Bis equivalent to!(A == B). -
A == Bis equivalent toB == A, except in the order of evaluation ofAandB.
The equality operator is not always transitive. For example, there might be two distinct String objects, each representing the same String value; each String object would be considered equal to the String value by the == operator, but the two String objects would not be equal to each other. For example:
-
new String("a") == "a"and"a" == new String("a")are bothtrue . -
new String("a") == new String("a")isfalse .
Comparison of Strings uses a simple equality test on sequences of code unit values. There is no attempt to use the more complex, semantically oriented definitions of character or string equality and collating order defined in the Unicode specification. Therefore Strings values that are canonically equal according to the Unicode Standard could test as unequal. In effect this algorithm assumes that both Strings are already in normalized form.
13.12 Binary Bitwise Operators
Syntax
13.12.1 Runtime Semantics: Evaluation
13.13 Binary Logical Operators
Syntax
The value produced by a && or || operator is not necessarily of type Boolean. The value produced will always be the value of one of the two operand expressions.
13.13.1 Runtime Semantics: Evaluation
- Let lRef be ?
Evaluation ofLogicalANDExpression . - Let lVal be ?
GetValue (lRef). - If
ToBoolean (lVal) isfalse , return lVal. - Let rRef be ?
Evaluation ofBitwiseORExpression . - Return ?
GetValue (rRef).
- Let lRef be ?
Evaluation ofLogicalORExpression . - Let lVal be ?
GetValue (lRef). - If
ToBoolean (lVal) istrue , return lVal. - Let rRef be ?
Evaluation ofLogicalANDExpression . - Return ?
GetValue (rRef).
- Let lRef be ?
Evaluation ofCoalesceExpressionHead . - Let lVal be ?
GetValue (lRef). - If lVal is either
undefined ornull , then- Let rRef be ?
Evaluation ofBitwiseORExpression . - Return ?
GetValue (rRef).
- Let rRef be ?
- Else,
- Return lVal.
13.14 Conditional Operator ( ? : )
Syntax
The grammar for a
13.14.1 Runtime Semantics: Evaluation
- Let lRef be ?
Evaluation ofShortCircuitExpression . - Let lVal be
ToBoolean (?GetValue (lRef)). - If lVal is
true , then- Let trueRef be ?
Evaluation of the firstAssignmentExpression . - Return ?
GetValue (trueRef).
- Let trueRef be ?
- Else,
- Let falseRef be ?
Evaluation of the secondAssignmentExpression . - Return ?
GetValue (falseRef).
- Let falseRef be ?
13.15 Assignment Operators
Syntax
13.15.1 Static Semantics: Early Errors
-
If
LeftHandSideExpression is either anObjectLiteral or anArrayLiteral ,LeftHandSideExpression must cover anAssignmentPattern . -
If
LeftHandSideExpression is neither anObjectLiteral nor anArrayLiteral , it is a Syntax Error if theAssignmentTargetType ofLeftHandSideExpression is notsimple .
-
It is a Syntax Error if the
AssignmentTargetType ofLeftHandSideExpression is notsimple .
13.15.2 Runtime Semantics: Evaluation
- If
LeftHandSideExpression is neither anObjectLiteral nor anArrayLiteral , then- Let lRef be ?
Evaluation ofLeftHandSideExpression . - If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue andIsIdentifierRef ofLeftHandSideExpression istrue , then- Let lhs be the
StringValue ofLeftHandSideExpression . - Let rVal be ?
NamedEvaluation ofAssignmentExpression with argument lhs.
- Let lhs be the
- Else,
- Let rRef be ?
Evaluation ofAssignmentExpression . - Let rVal be ?
GetValue (rRef).
- Let rRef be ?
- Perform ?
PutValue (lRef, rVal). - Return rVal.
- Let lRef be ?
- Let assignmentPattern be the
AssignmentPattern that iscovered byLeftHandSideExpression . - Let rRef be ?
Evaluation ofAssignmentExpression . - Let rVal be ?
GetValue (rRef). - Perform ?
DestructuringAssignmentEvaluation of assignmentPattern with argument rVal. - Return rVal.
- Let lRef be ?
Evaluation ofLeftHandSideExpression . - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation ofAssignmentExpression . - Let rVal be ?
GetValue (rRef). - Let assignmentOpText be the
source text matched by AssignmentOperator . - Let opText be the sequence of Unicode code points associated with assignmentOpText in the following table:
assignmentOpText opText **=***=*/=/%=%+=+-=-<<=<<>>=>>>>>=>>>&=&^=^|=| - Let r be ?
ApplyStringOrNumericBinaryOperator (lVal, opText, rVal). - Perform ?
PutValue (lRef, r). - Return r.
- Let lRef be ?
Evaluation ofLeftHandSideExpression . - Let lVal be ?
GetValue (lRef). - If
ToBoolean (lVal) isfalse , return lVal. - If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue andIsIdentifierRef ofLeftHandSideExpression istrue , then- Let lhs be the
StringValue ofLeftHandSideExpression . - Let rVal be ?
NamedEvaluation ofAssignmentExpression with argument lhs.
- Let lhs be the
- Else,
- Let rRef be ?
Evaluation ofAssignmentExpression . - Let rVal be ?
GetValue (rRef).
- Let rRef be ?
- Perform ?
PutValue (lRef, rVal). - Return rVal.
- Let lRef be ?
Evaluation ofLeftHandSideExpression . - Let lVal be ?
GetValue (lRef). - If
ToBoolean (lVal) istrue , return lVal. - If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue andIsIdentifierRef ofLeftHandSideExpression istrue , then- Let lhs be the
StringValue ofLeftHandSideExpression . - Let rVal be ?
NamedEvaluation ofAssignmentExpression with argument lhs.
- Let lhs be the
- Else,
- Let rRef be ?
Evaluation ofAssignmentExpression . - Let rVal be ?
GetValue (rRef).
- Let rRef be ?
- Perform ?
PutValue (lRef, rVal). - Return rVal.
- Let lRef be ?
Evaluation ofLeftHandSideExpression . - Let lVal be ?
GetValue (lRef). - If lVal is neither
undefined nornull , return lVal. - If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue andIsIdentifierRef ofLeftHandSideExpression istrue , then- Let lhs be the
StringValue ofLeftHandSideExpression . - Let rVal be ?
NamedEvaluation ofAssignmentExpression with argument lhs.
- Let lhs be the
- Else,
- Let rRef be ?
Evaluation ofAssignmentExpression . - Let rVal be ?
GetValue (rRef).
- Let rRef be ?
- Perform ?
PutValue (lRef, rVal). - Return rVal.
When this expression occurs within
13.15.3 ApplyStringOrNumericBinaryOperator ( lVal, opText, rVal )
The abstract operation ApplyStringOrNumericBinaryOperator takes arguments lVal (an **, *, /, %, +, -, <<, >>, >>>, &, ^, or |), and rVal (an
- If opText is
+, then- Let lPrim be ?
ToPrimitive (lVal). - Let rPrim be ?
ToPrimitive (rVal). - If lPrim
is a String or rPrimis a String , then- Let lStr be ?
ToString (lPrim). - Let rStr be ?
ToString (rPrim). - Return the
string-concatenation of lStr and rStr.
- Let lStr be ?
- Set lVal to lPrim.
- Set rVal to rPrim.
- Let lPrim be ?
- NOTE: At this point, it must be a numeric operation.
- Let lNum be ?
ToNumeric (lVal). - Let rNum be ?
ToNumeric (rVal). - If
SameType (lNum, rNum) isfalse , throw aTypeError exception. - If lNum
is a BigInt , then- If opText is
**, return ?BigInt::exponentiate (lNum, rNum). - If opText is
/, return ?BigInt::divide (lNum, rNum). - If opText is
%, return ?BigInt::remainder (lNum, rNum). - If opText is
>>>, return ?BigInt::unsignedRightShift (lNum, rNum). - Let operation be the abstract operation associated with opText in the following table:
opText operation *BigInt::multiply +BigInt::add -BigInt::subtract <<BigInt::leftShift >>BigInt::signedRightShift &BigInt::bitwiseAND ^BigInt::bitwiseXOR |BigInt::bitwiseOR
- If opText is
- Else,
Assert : lNumis a Number .- Let operation be the abstract operation associated with opText in the following table:
opText operation **Number::exponentiate *Number::multiply /Number::divide %Number::remainder +Number::add -Number::subtract <<Number::leftShift >>Number::signedRightShift >>>Number::unsignedRightShift &Number::bitwiseAND ^Number::bitwiseXOR |Number::bitwiseOR
- Return operation(lNum, rNum).
No hint is provided in the calls to
Step
13.15.4 EvaluateStringOrNumericBinaryExpression ( leftOperand, opText, rightOperand )
The abstract operation EvaluateStringOrNumericBinaryExpression takes arguments leftOperand (a
- Let lRef be ?
Evaluation of leftOperand. - Let lVal be ?
GetValue (lRef). - Let rRef be ?
Evaluation of rightOperand. - Let rVal be ?
GetValue (rRef). - Return ?
ApplyStringOrNumericBinaryOperator (lVal, opText, rVal).
13.15.5 Destructuring Assignment
Supplemental Syntax
In certain circumstances when processing an instance of the production
the interpretation of
13.15.5.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
AssignmentTargetType ofIdentifierReference is notsimple .
-
It is a Syntax Error if
DestructuringAssignmentTarget is either anArrayLiteral or anObjectLiteral .
-
If
LeftHandSideExpression is either anObjectLiteral or anArrayLiteral ,LeftHandSideExpression must cover anAssignmentPattern . -
If
LeftHandSideExpression is neither anObjectLiteral nor anArrayLiteral , it is a Syntax Error if theAssignmentTargetType ofLeftHandSideExpression is notsimple .
13.15.5.2 Runtime Semantics: DestructuringAssignmentEvaluation
The
- Perform ?
RequireObjectCoercible (value). - Return
unused .
- Perform ?
RequireObjectCoercible (value). - Perform ?
PropertyDestructuringAssignmentEvaluation ofAssignmentPropertyList with argument value. - Return
unused .
- Perform ?
RequireObjectCoercible (value). - Let excludedNames be a new empty
List . - Return ?
RestDestructuringAssignmentEvaluation ofAssignmentRestProperty with arguments value and excludedNames.
- Perform ?
RequireObjectCoercible (value). - Let excludedNames be ?
PropertyDestructuringAssignmentEvaluation ofAssignmentPropertyList with argument value. - Return ?
RestDestructuringAssignmentEvaluation ofAssignmentRestProperty with arguments value and excludedNames.
- Let iteratorRecord be ?
GetIterator (value,sync ). - Return ?
IteratorClose (iteratorRecord,NormalCompletion (unused )).
- Let iteratorRecord be ?
GetIterator (value,sync ). - Let result be
Completion (IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord). - If iteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord, result). - Return result.
- Let iteratorRecord be ?
GetIterator (value,sync ). - If
Elision is present, then- Let status be
Completion (IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord). - If status is an
abrupt completion , thenAssert : iteratorRecord.[[Done]] istrue .- Return ? status.
- Let status be
- Let result be
Completion (IteratorDestructuringAssignmentEvaluation ofAssignmentRestElement with argument iteratorRecord). - If iteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord, result). - Return result.
- Let iteratorRecord be ?
GetIterator (value,sync ). - Let result be
Completion (IteratorDestructuringAssignmentEvaluation ofAssignmentElementList with argument iteratorRecord). - If iteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord, result). - Return result.
- Let iteratorRecord be ?
GetIterator (value,sync ). - Let status be
Completion (IteratorDestructuringAssignmentEvaluation ofAssignmentElementList with argument iteratorRecord). - If status is an
abrupt completion , then- If iteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord, status). - Return ? status.
- If iteratorRecord.[[Done]] is
- If
Elision is present, then- Set status to
Completion (IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord). - If status is an
abrupt completion , thenAssert : iteratorRecord.[[Done]] istrue .- Return ? status.
- Set status to
- If
AssignmentRestElement is present, then- Set status to
Completion (IteratorDestructuringAssignmentEvaluation ofAssignmentRestElement with argument iteratorRecord).
- Set status to
- If iteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord, status). - Return ? status.
13.15.5.3 Runtime Semantics: PropertyDestructuringAssignmentEvaluation
The
- Let propertyNames be ?
PropertyDestructuringAssignmentEvaluation ofAssignmentPropertyList with argument value. - Let nextNames be ?
PropertyDestructuringAssignmentEvaluation ofAssignmentProperty with argument value. - Return the
list-concatenation of propertyNames and nextNames.
- Let P be the
StringValue ofIdentifierReference . - Let lRef be ?
ResolveBinding (P). - Let v be ?
GetV (value, P). - If
Initializer is present and v isundefined , then- If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Set v to ?
NamedEvaluation ofInitializer with argument P.
- Set v to ?
- Else,
- Let defaultValue be ?
Evaluation ofInitializer . - Set v to ?
GetValue (defaultValue).
- Let defaultValue be ?
- If
- Perform ?
PutValue (lRef, v). - Return « P ».
- Let name be ?
Evaluation ofPropertyName . - Perform ?
KeyedDestructuringAssignmentEvaluation ofAssignmentElement with arguments value and name. - Return « name ».
13.15.5.4 Runtime Semantics: RestDestructuringAssignmentEvaluation
The
- Let lRef be ?
Evaluation ofDestructuringAssignmentTarget . - Let restObj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform ?
CopyDataProperties (restObj, value, excludedNames). - Return ?
PutValue (lRef, restObj).
13.15.5.5 Runtime Semantics: IteratorDestructuringAssignmentEvaluation
The
- Return ?
IteratorDestructuringAssignmentEvaluation ofAssignmentElisionElement with argument iteratorRecord.
- Perform ?
IteratorDestructuringAssignmentEvaluation ofAssignmentElementList with argument iteratorRecord. - Return ?
IteratorDestructuringAssignmentEvaluation ofAssignmentElisionElement with argument iteratorRecord.
- Return ?
IteratorDestructuringAssignmentEvaluation ofAssignmentElement with argument iteratorRecord.
- Perform ?
IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord. - Return ?
IteratorDestructuringAssignmentEvaluation ofAssignmentElement with argument iteratorRecord.
- If iteratorRecord.[[Done]] is
false , then- Perform ?
IteratorStep (iteratorRecord).
- Perform ?
- Return
unused .
- Perform ?
IteratorDestructuringAssignmentEvaluation ofElision with argument iteratorRecord. - If iteratorRecord.[[Done]] is
false , then- Perform ?
IteratorStep (iteratorRecord).
- Perform ?
- Return
unused .
- If
DestructuringAssignmentTarget is neither anObjectLiteral nor anArrayLiteral , then- Let lRef be ?
Evaluation ofDestructuringAssignmentTarget .
- Let lRef be ?
- Let value be
undefined . - If iteratorRecord.[[Done]] is
false , then- Let next be ?
IteratorStepValue (iteratorRecord). - If next is not
done , then- Set value to next.
- Let next be ?
- If
Initializer is present and value isundefined , then- If
IsAnonymousFunctionDefinition (Initializer ) istrue andIsIdentifierRef ofDestructuringAssignmentTarget istrue , then- Let target be the
StringValue ofDestructuringAssignmentTarget . - Let v be ?
NamedEvaluation ofInitializer with argument target.
- Let target be the
- Else,
- Let defaultValue be ?
Evaluation ofInitializer . - Let v be ?
GetValue (defaultValue).
- Let defaultValue be ?
- If
- Else,
- Let v be value.
- If
DestructuringAssignmentTarget is either anObjectLiteral or anArrayLiteral , then- Let nestedAssignmentPattern be the
AssignmentPattern that iscovered byDestructuringAssignmentTarget . - Return ?
DestructuringAssignmentEvaluation of nestedAssignmentPattern with argument v.
- Let nestedAssignmentPattern be the
- Return ?
PutValue (lRef, v).
Left to right evaluation order is maintained by evaluating a
- If
DestructuringAssignmentTarget is neither anObjectLiteral nor anArrayLiteral , then- Let lRef be ?
Evaluation ofDestructuringAssignmentTarget .
- Let lRef be ?
- Let A be !
ArrayCreate (0). - Let n be 0.
- Repeat, while iteratorRecord.[[Done]] is
false ,- Let next be ?
IteratorStepValue (iteratorRecord). - If next is not
done , then- Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)), next). - Set n to n + 1.
- Perform !
- Let next be ?
- If
DestructuringAssignmentTarget is neither anObjectLiteral nor anArrayLiteral , then- Return ?
PutValue (lRef, A).
- Return ?
- Let nestedAssignmentPattern be the
AssignmentPattern that iscovered byDestructuringAssignmentTarget . - Return ?
DestructuringAssignmentEvaluation of nestedAssignmentPattern with argument A.
13.15.5.6 Runtime Semantics: KeyedDestructuringAssignmentEvaluation
The
- If
DestructuringAssignmentTarget is neither anObjectLiteral nor anArrayLiteral , then- Let lRef be ?
Evaluation ofDestructuringAssignmentTarget .
- Let lRef be ?
- Let v be ?
GetV (value, propertyName). - If
Initializer is present and v isundefined , then- If
IsAnonymousFunctionDefinition (Initializer ) istrue andIsIdentifierRef ofDestructuringAssignmentTarget istrue , then- Let target be the
StringValue ofDestructuringAssignmentTarget . - Let rhsValue be ?
NamedEvaluation ofInitializer with argument target.
- Let target be the
- Else,
- Let defaultValue be ?
Evaluation ofInitializer . - Let rhsValue be ?
GetValue (defaultValue).
- Let defaultValue be ?
- If
- Else,
- Let rhsValue be v.
- If
DestructuringAssignmentTarget is either anObjectLiteral or anArrayLiteral , then- Let assignmentPattern be the
AssignmentPattern that iscovered byDestructuringAssignmentTarget . - Return ?
DestructuringAssignmentEvaluation of assignmentPattern with argument rhsValue.
- Let assignmentPattern be the
- Return ?
PutValue (lRef, rhsValue).
13.16 Comma Operator ( , )
Syntax
13.16.1 Runtime Semantics: Evaluation
- Let lRef be ?
Evaluation ofExpression . - Perform ?
GetValue (lRef). - Let rRef be ?
Evaluation ofAssignmentExpression . - Return ?
GetValue (rRef).
14 ECMAScript Language: Statements and Declarations
Syntax
14.1 Statement Semantics
14.1.1 Runtime Semantics: Evaluation
- Return
empty .
- Return ?
Evaluation ofFunctionDeclaration .
- Let newLabelSet be a new empty
List . - Return ?
LabelledEvaluation of thisBreakableStatement with argument newLabelSet.
14.2 Block
Syntax
14.2.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
LexicallyDeclaredNames ofStatementList contains any duplicate entries. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofStatementList also occurs in theVarDeclaredNames ofStatementList .
14.2.2 Runtime Semantics: Evaluation
- Return
empty .
- Let oldEnv be the
running execution context 's LexicalEnvironment. - Let blockEnv be
NewDeclarativeEnvironment (oldEnv). - Perform
BlockDeclarationInstantiation (StatementList , blockEnv). - Set the
running execution context 's LexicalEnvironment to blockEnv. - Let blockValue be
Completion (Evaluation ofStatementList ). - Set the
running execution context 's LexicalEnvironment to oldEnv. - Return ? blockValue.
No matter how control leaves the
- Let sl be ?
Evaluation ofStatementList . - Let s be
Completion (Evaluation ofStatementListItem ). - Return ?
UpdateEmpty (s, sl).
The value of a eval function all return the value 1:
eval("1;;;;;")
eval("1;{}")
eval("1;var a;")14.2.3 BlockDeclarationInstantiation ( code, env )
The abstract operation BlockDeclarationInstantiation takes arguments code (a
When a
It performs the following steps when called:
- Let declarations be the
LexicallyScopedDeclarations of code. - Let privateEnv be the
running execution context 's PrivateEnvironment. - For each element d of declarations, do
- For each element dn of the
BoundNames of d, do- If
IsConstantDeclaration of d istrue , then- Perform ! env.CreateImmutableBinding(dn,
true ).
- Perform ! env.CreateImmutableBinding(dn,
- Else,
- Perform ! env.CreateMutableBinding(dn,
false ). NOTE: This step is replaced in sectionB.3.2.6 .
- Perform ! env.CreateMutableBinding(dn,
- If
- If d is either a
FunctionDeclaration , aGeneratorDeclaration , anAsyncFunctionDeclaration , or anAsyncGeneratorDeclaration , then- Let fn be the sole element of the
BoundNames of d. - Let fo be
InstantiateFunctionObject of d with arguments env and privateEnv. - Perform ! env.InitializeBinding(fn, fo). NOTE: This step is replaced in section
B.3.2.6 .
- Let fn be the sole element of the
- For each element dn of the
- Return
unused .
14.3 Declarations and the Variable Statement
14.3.1 Let and Const Declarations
let and const declarations define variables that are scoped to the let declaration does not have an
Syntax
14.3.1.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
BoundNames ofBindingList contains"let" . -
It is a Syntax Error if the
BoundNames ofBindingList contains any duplicate entries.
-
It is a Syntax Error if
Initializer is not present andIsConstantDeclaration of theLexicalDeclaration containing thisLexicalBinding istrue .
14.3.1.2 Runtime Semantics: Evaluation
- Perform ?
Evaluation ofBindingList . - Return
empty .
- Perform ?
Evaluation ofBindingList . - Return ?
Evaluation ofLexicalBinding .
- Let lhs be !
ResolveBinding (StringValue ofBindingIdentifier ). - Perform !
InitializeReferencedBinding (lhs,undefined ). - Return
empty .
A const declaration.
- Let bindingId be the
StringValue ofBindingIdentifier . - Let lhs be !
ResolveBinding (bindingId). - If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Let value be ?
NamedEvaluation ofInitializer with argument bindingId.
- Let value be ?
- Else,
- Let rhs be ?
Evaluation ofInitializer . - Let value be ?
GetValue (rhs).
- Let rhs be ?
- Perform !
InitializeReferencedBinding (lhs, value). - Return
empty .
- Let rhs be ?
Evaluation ofInitializer . - Let value be ?
GetValue (rhs). - Let env be the
running execution context 's LexicalEnvironment. - Return ?
BindingInitialization ofBindingPattern with arguments value and env.
14.3.2 Variable Statement
A var statement declares variables that are scoped to the
Syntax
14.3.2.1 Runtime Semantics: Evaluation
- Perform ?
Evaluation ofVariableDeclarationList . - Return
empty .
- Perform ?
Evaluation ofVariableDeclarationList . - Return ?
Evaluation ofVariableDeclaration .
- Return
empty .
- Let bindingId be the
StringValue ofBindingIdentifier . - Let lhs be ?
ResolveBinding (bindingId). - If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Let value be ?
NamedEvaluation ofInitializer with argument bindingId.
- Let value be ?
- Else,
- Let rhs be ?
Evaluation ofInitializer . - Let value be ?
GetValue (rhs).
- Let rhs be ?
- Perform ?
PutValue (lhs, value). - Return
empty .
If a
- Let rhs be ?
Evaluation ofInitializer . - Let rVal be ?
GetValue (rhs). - Return ?
BindingInitialization ofBindingPattern with arguments rVal andundefined .
14.3.3 Destructuring Binding Patterns
Syntax
14.3.3.1 Runtime Semantics: PropertyBindingInitialization
The
- Let boundNames be ?
PropertyBindingInitialization ofBindingPropertyList with arguments value and environment. - Let nextNames be ?
PropertyBindingInitialization ofBindingProperty with arguments value and environment. - Return the
list-concatenation of boundNames and nextNames.
- Let name be the sole element of the
BoundNames ofSingleNameBinding . - Perform ?
KeyedBindingInitialization ofSingleNameBinding with arguments value, environment, and name. - Return « name ».
- Let P be ?
Evaluation ofPropertyName . - Perform ?
KeyedBindingInitialization ofBindingElement with arguments value, environment, and P. - Return « P ».
14.3.3.2 Runtime Semantics: RestBindingInitialization
The
- Let lhs be ?
ResolveBinding (StringValue ofBindingIdentifier , environment). - Let restObj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform ?
CopyDataProperties (restObj, value, excludedNames). - If environment is
undefined , return ?PutValue (lhs, restObj). - Return ?
InitializeReferencedBinding (lhs, restObj).
14.3.3.3 Runtime Semantics: KeyedBindingInitialization
The
When
It is defined piecewise over the following productions:
- Let v be ?
GetV (value, propertyName). - If
Initializer is present and v isundefined , then- Let defaultValue be ?
Evaluation ofInitializer . - Set v to ?
GetValue (defaultValue).
- Let defaultValue be ?
- Return ?
BindingInitialization ofBindingPattern with arguments v and environment.
- Let bindingId be the
StringValue ofBindingIdentifier . - Let lhs be ?
ResolveBinding (bindingId, environment). - Let v be ?
GetV (value, propertyName). - If
Initializer is present and v isundefined , then- If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Set v to ?
NamedEvaluation ofInitializer with argument bindingId.
- Set v to ?
- Else,
- Let defaultValue be ?
Evaluation ofInitializer . - Set v to ?
GetValue (defaultValue).
- Let defaultValue be ?
- If
- If environment is
undefined , return ?PutValue (lhs, v). - Return ?
InitializeReferencedBinding (lhs, v).
14.4 Empty Statement
Syntax
14.4.1 Runtime Semantics: Evaluation
- Return
empty .
14.5 Expression Statement
Syntax
An function or class async function because that would make it ambiguous with an let [ because that would make it ambiguous with a let
14.5.1 Runtime Semantics: Evaluation
- Let exprRef be ?
Evaluation ofExpression . - Return ?
GetValue (exprRef).
14.6 The if Statement
Syntax
else] resolves the classic "dangling else" problem in the usual way. That is, when the choice of associated if is otherwise ambiguous, the else is associated with the nearest (innermost) of the candidate ifs14.6.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsLabelledFunction (the firstStatement ) istrue . -
It is a Syntax Error if
IsLabelledFunction (the secondStatement ) istrue .
-
It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply this rule if the extension specified in
14.6.2 Runtime Semantics: Evaluation
- Let exprRef be ?
Evaluation ofExpression . - Let exprValue be
ToBoolean (?GetValue (exprRef)). - If exprValue is
true , then- Let stmtCompletion be
Completion (Evaluation of the firstStatement ).
- Let stmtCompletion be
- Else,
- Let stmtCompletion be
Completion (Evaluation of the secondStatement ).
- Let stmtCompletion be
- Return ?
UpdateEmpty (stmtCompletion,undefined ).
- Let exprRef be ?
Evaluation ofExpression . - Let exprValue be
ToBoolean (?GetValue (exprRef)). - If exprValue is
false , then- Return
undefined .
- Return
- Else,
- Let stmtCompletion be
Completion (Evaluation ofStatement ). - Return ?
UpdateEmpty (stmtCompletion,undefined ).
- Let stmtCompletion be
14.7 Iteration Statements
Syntax
14.7.1 Semantics
14.7.1.1 LoopContinues ( completion, labelSet )
The abstract operation LoopContinues takes arguments completion (a
- If completion is a
normal completion , returntrue . - If completion is not a
continue completion , returnfalse . - If completion.[[Target]] is
empty , returntrue . - If labelSet contains completion.[[Target]], return
true . - Return
false .
Within the
14.7.1.2 Runtime Semantics: LoopEvaluation
The
- Return ?
DoWhileLoopEvaluation ofDoWhileStatement with argument labelSet.
- Return ?
WhileLoopEvaluation ofWhileStatement with argument labelSet.
- Return ?
ForLoopEvaluation ofForStatement with argument labelSet.
- Return ?
ForInOfLoopEvaluation ofForInOfStatement with argument labelSet.
14.7.2 The do-while Statement
Syntax
14.7.2.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply this rule if the extension specified in
14.7.2.2 Runtime Semantics: DoWhileLoopEvaluation
The
- Let V be
undefined . - Repeat,
- Let stmtResult be
Completion (Evaluation ofStatement ). - If
LoopContinues (stmtResult, labelSet) isfalse , return ?UpdateEmpty (stmtResult, V). - If stmtResult.[[Value]] is not
empty , set V to stmtResult.[[Value]]. - Let exprRef be ?
Evaluation ofExpression . - Let exprValue be ?
GetValue (exprRef). - If
ToBoolean (exprValue) isfalse , return V.
- Let stmtResult be
14.7.3 The while Statement
Syntax
14.7.3.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply this rule if the extension specified in
14.7.3.2 Runtime Semantics: WhileLoopEvaluation
The
- Let V be
undefined . - Repeat,
- Let exprRef be ?
Evaluation ofExpression . - Let exprValue be ?
GetValue (exprRef). - If
ToBoolean (exprValue) isfalse , return V. - Let stmtResult be
Completion (Evaluation ofStatement ). - If
LoopContinues (stmtResult, labelSet) isfalse , return ?UpdateEmpty (stmtResult, V). - If stmtResult.[[Value]] is not
empty , set V to stmtResult.[[Value]].
- Let exprRef be ?
14.7.4 The for Statement
Syntax
14.7.4.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply this rule if the extension specified in
-
It is a Syntax Error if any element of the
BoundNames ofLexicalDeclaration also occurs in theVarDeclaredNames ofStatement .
14.7.4.2 Runtime Semantics: ForLoopEvaluation
The
- If the first
Expression is present, then- Let exprRef be ?
Evaluation of the firstExpression . - Perform ?
GetValue (exprRef).
- Let exprRef be ?
- If the second
Expression is present, let test be the secondExpression ; otherwise, let test beempty . - If the third
Expression is present, let increment be the thirdExpression ; otherwise, let increment beempty . - Return ?
ForBodyEvaluation (test, increment,Statement , « », labelSet).
- Perform ?
Evaluation ofVariableDeclarationList . - If the first
Expression is present, let test be the firstExpression ; otherwise, let test beempty . - If the second
Expression is present, let increment be the secondExpression ; otherwise, let increment beempty . - Return ?
ForBodyEvaluation (test, increment,Statement , « », labelSet).
- Let oldEnv be the
running execution context 's LexicalEnvironment. - Let loopEnv be
NewDeclarativeEnvironment (oldEnv). - Let isConst be
IsConstantDeclaration ofLexicalDeclaration . - Let boundNames be the
BoundNames ofLexicalDeclaration . - For each element dn of boundNames, do
- If isConst is
true , then- Perform ! loopEnv.CreateImmutableBinding(dn,
true ).
- Perform ! loopEnv.CreateImmutableBinding(dn,
- Else,
- Perform ! loopEnv.CreateMutableBinding(dn,
false ).
- Perform ! loopEnv.CreateMutableBinding(dn,
- If isConst is
- Set the
running execution context 's LexicalEnvironment to loopEnv. - Let forDcl be
Completion (Evaluation ofLexicalDeclaration ). - If forDcl is an
abrupt completion , then- Set the
running execution context 's LexicalEnvironment to oldEnv. - Return ? forDcl.
- Set the
- If isConst is
false , let perIterationLets be boundNames; otherwise let perIterationLets be a new emptyList . - If the first
Expression is present, let test be the firstExpression ; otherwise, let test beempty . - If the second
Expression is present, let increment be the secondExpression ; otherwise, let increment beempty . - Let bodyResult be
Completion (ForBodyEvaluation (test, increment,Statement , perIterationLets, labelSet)). - Set the
running execution context 's LexicalEnvironment to oldEnv. - Return ? bodyResult.
14.7.4.3 ForBodyEvaluation ( test, increment, stmt, perIterationBindings, labelSet )
The abstract operation ForBodyEvaluation takes arguments test (an
- Let V be
undefined . - Perform ?
CreatePerIterationEnvironment (perIterationBindings). - Repeat,
- If test is not
empty , then- Let testRef be ?
Evaluation of test. - Let testValue be ?
GetValue (testRef). - If
ToBoolean (testValue) isfalse , return V.
- Let testRef be ?
- Let result be
Completion (Evaluation of stmt). - If
LoopContinues (result, labelSet) isfalse , return ?UpdateEmpty (result, V). - If result.[[Value]] is not
empty , set V to result.[[Value]]. - Perform ?
CreatePerIterationEnvironment (perIterationBindings). - If increment is not
empty , then- Let incRef be ?
Evaluation of increment. - Perform ?
GetValue (incRef).
- Let incRef be ?
- If test is not
14.7.4.4 CreatePerIterationEnvironment ( perIterationBindings )
The abstract operation CreatePerIterationEnvironment takes argument perIterationBindings (a
- If perIterationBindings has any elements, then
- Let lastIterationEnv be the
running execution context 's LexicalEnvironment. - Let outer be lastIterationEnv.[[OuterEnv]].
Assert : outer is notnull .- Let thisIterationEnv be
NewDeclarativeEnvironment (outer). - For each element bn of perIterationBindings, do
- Perform ! thisIterationEnv.CreateMutableBinding(bn,
false ). - Let lastValue be ? lastIterationEnv.GetBindingValue(bn,
true ). - Perform ! thisIterationEnv.InitializeBinding(bn, lastValue).
- Perform ! thisIterationEnv.CreateMutableBinding(bn,
- Set the
running execution context 's LexicalEnvironment to thisIterationEnv.
- Let lastIterationEnv be the
- Return
unused .
14.7.5 The for-in, for-of, and for-await-of Statements
Syntax
This section is extended by Annex
14.7.5.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply this rule if the extension specified in
-
If
LeftHandSideExpression is either anObjectLiteral or anArrayLiteral ,LeftHandSideExpression must cover anAssignmentPattern . -
If
LeftHandSideExpression is neither anObjectLiteral nor anArrayLiteral , it is a Syntax Error if theAssignmentTargetType ofLeftHandSideExpression is notsimple .
-
It is a Syntax Error if the
BoundNames ofForDeclaration contains"let" . -
It is a Syntax Error if any element of the
BoundNames ofForDeclaration also occurs in theVarDeclaredNames ofStatement . -
It is a Syntax Error if the
BoundNames ofForDeclaration contains any duplicate entries.
14.7.5.2 Static Semantics: IsDestructuring
The
- If
PrimaryExpression is either anObjectLiteral or anArrayLiteral , returntrue . - Return
false .
- Return
false .
- Return
IsDestructuring ofForBinding .
- Return
false .
- Return
true .
This section is extended by Annex
14.7.5.3 Runtime Semantics: ForDeclarationBindingInitialization
The
var statements and the formal parameter lists of some
It is defined piecewise over the following productions:
- Return ?
BindingInitialization ofForBinding with arguments value and environment.
14.7.5.4 Runtime Semantics: ForDeclarationBindingInstantiation
The
- For each element name of the
BoundNames ofForBinding , do- If
IsConstantDeclaration ofLetOrConst istrue , then- Perform ! environment.CreateImmutableBinding(name,
true ).
- Perform ! environment.CreateImmutableBinding(name,
- Else,
- Perform ! environment.CreateMutableBinding(name,
false ).
- Perform ! environment.CreateMutableBinding(name,
- If
- Return
unused .
14.7.5.5 Runtime Semantics: ForInOfLoopEvaluation
The
- Let keyResult be ?
ForIn/OfHeadEvaluation (« »,Expression ,enumerate ). - Return ?
ForIn/OfBodyEvaluation (LeftHandSideExpression ,Statement , keyResult,enumerate ,assignment , labelSet).
- Let keyResult be ?
ForIn/OfHeadEvaluation (« »,Expression ,enumerate ). - Return ?
ForIn/OfBodyEvaluation (ForBinding ,Statement , keyResult,enumerate ,var-binding , labelSet).
- Let keyResult be ?
ForIn/OfHeadEvaluation (BoundNames ofForDeclaration ,Expression ,enumerate ). - Return ?
ForIn/OfBodyEvaluation (ForDeclaration ,Statement , keyResult,enumerate ,lexical-binding , labelSet).
- Let keyResult be ?
ForIn/OfHeadEvaluation (« »,AssignmentExpression ,iterate ). - Return ?
ForIn/OfBodyEvaluation (LeftHandSideExpression ,Statement , keyResult,iterate ,assignment , labelSet).
- Let keyResult be ?
ForIn/OfHeadEvaluation (« »,AssignmentExpression ,iterate ). - Return ?
ForIn/OfBodyEvaluation (ForBinding ,Statement , keyResult,iterate ,var-binding , labelSet).
- Let keyResult be ?
ForIn/OfHeadEvaluation (BoundNames ofForDeclaration ,AssignmentExpression ,iterate ). - Return ?
ForIn/OfBodyEvaluation (ForDeclaration ,Statement , keyResult,iterate ,lexical-binding , labelSet).
- Let keyResult be ?
ForIn/OfHeadEvaluation (« »,AssignmentExpression ,async-iterate ). - Return ?
ForIn/OfBodyEvaluation (LeftHandSideExpression ,Statement , keyResult,iterate ,assignment , labelSet,async ).
- Let keyResult be ?
ForIn/OfHeadEvaluation (« »,AssignmentExpression ,async-iterate ). - Return ?
ForIn/OfBodyEvaluation (ForBinding ,Statement , keyResult,iterate ,var-binding , labelSet,async ).
- Let keyResult be ?
ForIn/OfHeadEvaluation (BoundNames ofForDeclaration ,AssignmentExpression ,async-iterate ). - Return ?
ForIn/OfBodyEvaluation (ForDeclaration ,Statement , keyResult,iterate ,lexical-binding , labelSet,async ).
This section is extended by Annex
14.7.5.6 ForIn/OfHeadEvaluation ( uninitializedBoundNames, expr, iterationKind )
The abstract operation ForIn/OfHeadEvaluation takes arguments uninitializedBoundNames (a
- Let oldEnv be the
running execution context 's LexicalEnvironment. - If uninitializedBoundNames is not empty, then
Assert : uninitializedBoundNames has no duplicate entries.- Let newEnv be
NewDeclarativeEnvironment (oldEnv). - For each String name of uninitializedBoundNames, do
- Perform ! newEnv.CreateMutableBinding(name,
false ).
- Perform ! newEnv.CreateMutableBinding(name,
- Set the
running execution context 's LexicalEnvironment to newEnv.
- Let exprRef be
Completion (Evaluation of expr). - Set the
running execution context 's LexicalEnvironment to oldEnv. - Let exprValue be ?
GetValue (? exprRef). - If iterationKind is
enumerate , then- If exprValue is either
undefined ornull , then- Return
Completion Record { [[Type]]:break , [[Value]]:empty , [[Target]]:empty }.
- Return
- Let obj be !
ToObject (exprValue). - Let iterator be
EnumerateObjectProperties (obj). - Let nextMethod be !
GetV (iterator,"next" ). - Return the
Iterator Record { [[Iterator]]: iterator, [[NextMethod]]: nextMethod, [[Done]]:false }.
- If exprValue is either
- Else,
Assert : iterationKind is eitheriterate orasync-iterate .- If iterationKind is
async-iterate , let iteratorKind beasync . - Else, let iteratorKind be
sync . - Return ?
GetIterator (exprValue, iteratorKind).
14.7.5.7 ForIn/OfBodyEvaluation ( lhs, stmt, iteratorRecord, iterationKind, lhsKind, labelSet [ , iteratorKind ] )
The abstract operation ForIn/OfBodyEvaluation takes arguments lhs (a
- If iteratorKind is not present, set iteratorKind to
sync . - Let oldEnv be the
running execution context 's LexicalEnvironment. - Let V be
undefined . - Let destructuring be
IsDestructuring of lhs. - If destructuring is
true and lhsKind isassignment , thenAssert : lhs is aLeftHandSideExpression .- Let assignmentPattern be the
AssignmentPattern that iscovered by lhs.
- Repeat,
- Let nextResult be ?
Call (iteratorRecord.[[NextMethod]], iteratorRecord.[[Iterator]]). - If iteratorKind is
async , set nextResult to ?Await (nextResult). - If nextResult
is not an Object , throw aTypeError exception. - Let done be ?
IteratorComplete (nextResult). - If done is
true , return V. - Let nextValue be ?
IteratorValue (nextResult). - If lhsKind is either
assignment orvar-binding , then- If destructuring is
true , then- If lhsKind is
assignment , then- Let status be
Completion (DestructuringAssignmentEvaluation of assignmentPattern with argument nextValue).
- Let status be
- Else,
Assert : lhsKind isvar-binding .Assert : lhs is aForBinding .- Let status be
Completion (BindingInitialization of lhs with arguments nextValue andundefined ).
- If lhsKind is
- Else,
- Let lhsRef be
Completion (Evaluation of lhs). (It may be evaluated repeatedly.) - If lhsRef is an
abrupt completion , then- Let status be lhsRef.
- Else,
- Let status be
Completion (PutValue (lhsRef.[[Value]], nextValue)).
- Let status be
- Let lhsRef be
- If destructuring is
- Else,
Assert : lhsKind islexical-binding .Assert : lhs is aForDeclaration .- Let iterationEnv be
NewDeclarativeEnvironment (oldEnv). - Perform
ForDeclarationBindingInstantiation of lhs with argument iterationEnv. - Set the
running execution context 's LexicalEnvironment to iterationEnv. - If destructuring is
true , then- Let status be
Completion (ForDeclarationBindingInitialization of lhs with arguments nextValue and iterationEnv).
- Let status be
- Else,
Assert : lhs binds a single name.- Let lhsName be the sole element of the
BoundNames of lhs. - Let lhsRef be !
ResolveBinding (lhsName). - Let status be
Completion (InitializeReferencedBinding (lhsRef, nextValue)).
- If status is an
abrupt completion , then- Set the
running execution context 's LexicalEnvironment to oldEnv. - If iteratorKind is
async , return ?AsyncIteratorClose (iteratorRecord, status). - If iterationKind is
enumerate , then- Return ? status.
- Else,
Assert : iterationKind isiterate .- Return ?
IteratorClose (iteratorRecord, status).
- Set the
- Let result be
Completion (Evaluation of stmt). - Set the
running execution context 's LexicalEnvironment to oldEnv. - If
LoopContinues (result, labelSet) isfalse , then- If iterationKind is
enumerate , then- Return ?
UpdateEmpty (result, V).
- Return ?
- Else,
Assert : iterationKind isiterate .- Set status to
Completion (UpdateEmpty (result, V)). - If iteratorKind is
async , return ?AsyncIteratorClose (iteratorRecord, status). - Return ?
IteratorClose (iteratorRecord, status).
- If iterationKind is
- If result.[[Value]] is not
empty , set V to result.[[Value]].
- Let nextResult be ?
14.7.5.8 Runtime Semantics: Evaluation
- Let bindingId be the
StringValue ofBindingIdentifier . - Return ?
ResolveBinding (bindingId).
14.7.5.9 EnumerateObjectProperties ( O )
The abstract operation EnumerateObjectProperties takes argument O (an Object) and returns an
- Return an
iterator object whosenextmethod iterates over all the String-valued keys of enumerable properties of O. Theiterator object is never directly accessible to ECMAScript code. The mechanics and order of enumerating the properties is not specified but must conform to the rules specified below.
The throw and return methods are next method processes object properties to determine whether the next method is ignored. If new properties are added to the target object during enumeration, the newly added properties are not guaranteed to be processed in the active enumeration. A next method at most once in any enumeration.
Enumerating the properties of the target object includes enumerating properties of its prototype, and the prototype of the prototype, and so on, recursively; but a property of a prototype is not processed if it has the same name as a property that has already been processed by the next method. The values of [[Enumerable]] attributes are not considered when determining if a property of a prototype object has already been processed. The enumerable property names of prototype objects must be obtained by invoking EnumerateObjectProperties passing the prototype object as the argument. EnumerateObjectProperties must obtain the own
In addition, if neither O nor any object in its prototype chain is a
- the value of the [[Prototype]] internal slot of O or an object in its prototype chain changes,
- a property is removed from O or an object in its prototype chain,
- a property is added to an object in O's prototype chain, or
- the value of the [[Enumerable]] attribute of a property of O or an object in its prototype chain changes.
ECMAScript implementations are not required to implement the algorithm in
The following is an informative definition of an ECMAScript generator function that conforms to these rules:
function* EnumerateObjectProperties(obj) {
const visited = new Set();
for (const key of Reflect.ownKeys(obj)) {
if (typeof key === "symbol") continue;
const desc = Reflect.getOwnPropertyDescriptor(obj, key);
if (desc) {
visited.add(key);
if (desc.enumerable) yield key;
}
}
const proto = Reflect.getPrototypeOf(obj);
if (proto === null) return;
for (const protoKey of EnumerateObjectProperties(proto)) {
if (!visited.has(protoKey)) yield protoKey;
}
}14.7.5.10 For-In Iterator Objects
A For-In Iterator is an object that represents a specific iteration over some specific object. For-In Iterator objects are never directly accessible to ECMAScript code; they exist solely to illustrate the behaviour of
14.7.5.10.1 CreateForInIterator ( object )
The abstract operation CreateForInIterator takes argument object (an Object) and returns a
- Let iterator be
OrdinaryObjectCreate (%ForInIteratorPrototype% , « [[Object]], [[ObjectWasVisited]], [[VisitedKeys]], [[RemainingKeys]] »). - Set iterator.[[Object]] to object.
- Set iterator.[[ObjectWasVisited]] to
false . - Set iterator.[[VisitedKeys]] to a new empty
List . - Set iterator.[[RemainingKeys]] to a new empty
List . - Return iterator.
14.7.5.10.2 The %ForInIteratorPrototype% Object
The %ForInIteratorPrototype% object:
- has properties that are inherited by all
For-In Iterator objects . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Iterator.prototype% . - is never directly accessible to ECMAScript code.
- has the following properties:
14.7.5.10.2.1 %ForInIteratorPrototype%.next ( )
- Let O be the
this value. Assert : Ois an Object .Assert : O has all of the internal slots of aFor-In Iterator instance (14.7.5.10.3 ).- Let object be O.[[Object]].
- Repeat,
- If O.[[ObjectWasVisited]] is
false , then- Let keys be ? object.[[OwnPropertyKeys]]().
- For each element key of keys, do
- If key
is a String , then- Append key to O.[[RemainingKeys]].
- If key
- Set O.[[ObjectWasVisited]] to
true .
- Repeat, while O.[[RemainingKeys]] is not empty,
- Let r be the first element of O.[[RemainingKeys]].
- Remove the first element from O.[[RemainingKeys]].
- If O.[[VisitedKeys]] does not contain r, then
- Let desc be ? object.[[GetOwnProperty]](r).
- If desc is not
undefined , then- Append r to O.[[VisitedKeys]].
- If desc.[[Enumerable]] is
true , returnCreateIteratorResultObject (r,false ).
- Set object to ? object.[[GetPrototypeOf]]().
- Set O.[[Object]] to object.
- Set O.[[ObjectWasVisited]] to
false . - If object is
null , returnCreateIteratorResultObject (undefined ,true ).
- If O.[[ObjectWasVisited]] is
14.7.5.10.3 Properties of For-In Iterator Instances
| Internal Slot | Type | Description |
|---|---|---|
| [[Object]] | an Object | The Object value whose properties are being iterated. |
| [[ObjectWasVisited]] | a Boolean |
|
| [[VisitedKeys]] |
a |
The values that have been emitted by this |
| [[RemainingKeys]] |
a |
The values remaining to be emitted for the current object, before iterating the properties of its prototype (if its prototype is not |
14.8 The continue Statement
Syntax
14.8.1 Static Semantics: Early Errors
-
It is a Syntax Error if this
ContinueStatement is not nested, directly or indirectly (but not crossing function orstaticinitialization block boundaries), within anIterationStatement .
14.8.2 Runtime Semantics: Evaluation
- Return
Completion Record { [[Type]]:continue , [[Value]]:empty , [[Target]]:empty }.
- Let label be the
StringValue ofLabelIdentifier . - Return
Completion Record { [[Type]]:continue , [[Value]]:empty , [[Target]]: label }.
14.9 The break Statement
Syntax
14.9.1 Static Semantics: Early Errors
-
It is a Syntax Error if this
BreakStatement is not nested, directly or indirectly (but not crossing function orstaticinitialization block boundaries), within anIterationStatement or aSwitchStatement .
14.9.2 Runtime Semantics: Evaluation
- Return
Completion Record { [[Type]]:break , [[Value]]:empty , [[Target]]:empty }.
- Let label be the
StringValue ofLabelIdentifier . - Return
Completion Record { [[Type]]:break , [[Value]]:empty , [[Target]]: label }.
14.10 The return Statement
Syntax
A return statement causes a function to cease execution and, in most cases, returns a value to the caller. If return statement may not actually return a value to the caller depending on surrounding context. For example, in a try block, a return statement's finally block.
14.10.1 Runtime Semantics: Evaluation
- Return
ReturnCompletion (undefined ).
- Let exprRef be ?
Evaluation ofExpression . - Let exprValue be ?
GetValue (exprRef). - If
GetGeneratorKind () isasync , set exprValue to ?Await (exprValue). - Return
ReturnCompletion (exprValue).
14.11 The with Statement
Use of the with statement is discouraged in new ECMAScript code. Consider alternatives that are permitted in both
Syntax
The with statement adds an
14.11.1 Static Semantics: Early Errors
-
It is a Syntax Error if
IsStrict (this production) istrue . -
It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply the second rule if the extension specified in
14.11.2 Runtime Semantics: Evaluation
- Let val be ?
Evaluation ofExpression . - Let obj be ?
ToObject (?GetValue (val)). - Let oldEnv be the
running execution context 's LexicalEnvironment. - Let newEnv be
NewObjectEnvironment (obj,true , oldEnv). - Set the
running execution context 's LexicalEnvironment to newEnv. - Let C be
Completion (Evaluation ofStatement ). - Set the
running execution context 's LexicalEnvironment to oldEnv. - Return ?
UpdateEmpty (C,undefined ).
No matter how control leaves the embedded
14.12 The switch Statement
Syntax
14.12.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
LexicallyDeclaredNames ofCaseBlock contains any duplicate entries. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofCaseBlock also occurs in theVarDeclaredNames ofCaseBlock .
14.12.2 Runtime Semantics: CaseBlockEvaluation
The
- Return
undefined .
- Let V be
undefined . - Let A be the
List ofCaseClause items inCaseClauses , in source text order. - Let found be
false . - For each
CaseClause C of A, do- If found is
false , then- Set found to ?
CaseClauseIsSelected (C, input).
- Set found to ?
- If found is
true , then- Let R be
Completion (Evaluation of C). - If R.[[Value]] is not
empty , set V to R.[[Value]]. - If R is an
abrupt completion , return ?UpdateEmpty (R, V).
- Let R be
- If found is
- Return V.
- Let V be
undefined . - If the first
CaseClauses is present, then- Let A be the
List ofCaseClause items in the firstCaseClauses , in source text order.
- Let A be the
- Else,
- Let A be a new empty
List .
- Let A be a new empty
- Let found be
false . - For each
CaseClause C of A, do- If found is
false , then- Set found to ?
CaseClauseIsSelected (C, input).
- Set found to ?
- If found is
true , then- Let R be
Completion (Evaluation of C). - If R.[[Value]] is not
empty , set V to R.[[Value]]. - If R is an
abrupt completion , return ?UpdateEmpty (R, V).
- Let R be
- If found is
- Let foundInB be
false . - If the second
CaseClauses is present, then- Let B be the
List ofCaseClause items in the secondCaseClauses , in source text order.
- Let B be the
- Else,
- Let B be a new empty
List .
- Let B be a new empty
- If found is
false , then- For each
CaseClause C of B, do- If foundInB is
false , then- Set foundInB to ?
CaseClauseIsSelected (C, input).
- Set foundInB to ?
- If foundInB is
true , then- Let R be
Completion (Evaluation ofCaseClause C). - If R.[[Value]] is not
empty , set V to R.[[Value]]. - If R is an
abrupt completion , return ?UpdateEmpty (R, V).
- Let R be
- If foundInB is
- For each
- If foundInB is
true , return V. - Let defaultR be
Completion (Evaluation ofDefaultClause ). - If defaultR.[[Value]] is not
empty , set V to defaultR.[[Value]]. - If defaultR is an
abrupt completion , return ?UpdateEmpty (defaultR, V). - NOTE: The following is another complete iteration of the second
CaseClauses . - For each
CaseClause C of B, do- Let R be
Completion (Evaluation ofCaseClause C). - If R.[[Value]] is not
empty , set V to R.[[Value]]. - If R is an
abrupt completion , return ?UpdateEmpty (R, V).
- Let R be
- Return V.
14.12.3 CaseClauseIsSelected ( C, input )
The abstract operation CaseClauseIsSelected takes arguments C (a
Assert : C is an instance of the productionCaseClause : case Expression : StatementList opt - Let exprRef be ?
Evaluation of theExpression of C. - Let clauseSelector be ?
GetValue (exprRef). - Return
IsStrictlyEqual (input, clauseSelector).
This operation does not execute C's
14.12.4 Runtime Semantics: Evaluation
- Let exprRef be ?
Evaluation ofExpression . - Let switchValue be ?
GetValue (exprRef). - Let oldEnv be the
running execution context 's LexicalEnvironment. - Let blockEnv be
NewDeclarativeEnvironment (oldEnv). - Perform
BlockDeclarationInstantiation (CaseBlock , blockEnv). - Set the
running execution context 's LexicalEnvironment to blockEnv. - Let R be
Completion (CaseBlockEvaluation ofCaseBlock with argument switchValue). - Set the
running execution context 's LexicalEnvironment to oldEnv. - Return R.
No matter how control leaves the
- Return
empty .
- Return ?
Evaluation ofStatementList .
- Return
empty .
- Return ?
Evaluation ofStatementList .
14.13 Labelled Statements
Syntax
A break and continue statements. ECMAScript has no goto statement. A
14.13.1 Static Semantics: Early Errors
- It is a Syntax Error if any source text is matched by this production.
An alternative definition for this rule is provided in
14.13.2 Static Semantics: IsLabelledFunction ( stmt )
The abstract operation IsLabelledFunction takes argument stmt (a
- If stmt is not a
LabelledStatement , returnfalse . - Let item be the
LabelledItem of stmt. - If item is
LabelledItem : FunctionDeclaration true . - Let subStmt be the
Statement of item. - Return
IsLabelledFunction (subStmt).
14.13.3 Runtime Semantics: Evaluation
- Return ?
LabelledEvaluation of thisLabelledStatement with argument « ».
14.13.4 Runtime Semantics: LabelledEvaluation
The
- Let stmtResult be
Completion (LoopEvaluation ofIterationStatement with argument labelSet). - If stmtResult is a
break completion , then- If stmtResult.[[Target]] is
empty , then- If stmtResult.[[Value]] is
empty , set stmtResult toNormalCompletion (undefined ). - Else, set stmtResult to
NormalCompletion (stmtResult.[[Value]]).
- If stmtResult.[[Value]] is
- If stmtResult.[[Target]] is
- Return ? stmtResult.
- Let stmtResult be
Completion (Evaluation ofSwitchStatement ). - If stmtResult is a
break completion , then- If stmtResult.[[Target]] is
empty , then- If stmtResult.[[Value]] is
empty , set stmtResult toNormalCompletion (undefined ). - Else, set stmtResult to
NormalCompletion (stmtResult.[[Value]]).
- If stmtResult.[[Value]] is
- If stmtResult.[[Target]] is
- Return ? stmtResult.
A
- Let label be the
StringValue ofLabelIdentifier . - Let newLabelSet be the
list-concatenation of labelSet and « label ». - Let stmtResult be
Completion (LabelledEvaluation ofLabelledItem with argument newLabelSet). - If stmtResult is a
break completion and stmtResult.[[Target]] is label, then- Set stmtResult to
NormalCompletion (stmtResult.[[Value]]).
- Set stmtResult to
- Return ? stmtResult.
- Return ?
Evaluation ofFunctionDeclaration .
- Return ?
Evaluation ofStatement .
The only two productions of
14.14 The throw Statement
Syntax
14.14.1 Runtime Semantics: Evaluation
- Let exprRef be ?
Evaluation ofExpression . - Let exprValue be ?
GetValue (exprRef). - Return
ThrowCompletion (exprValue).
14.15 The try Statement
Syntax
The try statement encloses a block of code in which an exceptional condition can occur, such as a runtime error or a throw statement. The catch clause provides the exception-handling code. When a catch clause catches an exception, its
14.15.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
BoundNames ofCatchParameter contains any duplicate elements. -
It is a Syntax Error if any element of the
BoundNames ofCatchParameter also occurs in theLexicallyDeclaredNames ofBlock . -
It is a Syntax Error if any element of the
BoundNames ofCatchParameter also occurs in theVarDeclaredNames ofBlock .
An alternative
14.15.2 Runtime Semantics: CatchClauseEvaluation
The
- Let oldEnv be the
running execution context 's LexicalEnvironment. - Let catchEnv be
NewDeclarativeEnvironment (oldEnv). - For each element argName of the
BoundNames ofCatchParameter , do- Perform ! catchEnv.CreateMutableBinding(argName,
false ).
- Perform ! catchEnv.CreateMutableBinding(argName,
- Set the
running execution context 's LexicalEnvironment to catchEnv. - Let status be
Completion (BindingInitialization ofCatchParameter with arguments thrownValue and catchEnv). - If status is an
abrupt completion , then- Set the
running execution context 's LexicalEnvironment to oldEnv. - Return ? status.
- Set the
- Let B be
Completion (Evaluation ofBlock ). - Set the
running execution context 's LexicalEnvironment to oldEnv. - Return ? B.
- Return ?
Evaluation ofBlock .
No matter how control leaves the
14.15.3 Runtime Semantics: Evaluation
- Let B be
Completion (Evaluation ofBlock ). - If B is a
throw completion , let C beCompletion (CatchClauseEvaluation ofCatch with argument B.[[Value]]). - Else, let C be B.
- Return ?
UpdateEmpty (C,undefined ).
- Let B be
Completion (Evaluation ofBlock ). - Let F be
Completion (Evaluation ofFinally ). - If F is a
normal completion , set F to B. - Return ?
UpdateEmpty (F,undefined ).
- Let B be
Completion (Evaluation ofBlock ). - If B is a
throw completion , let C beCompletion (CatchClauseEvaluation ofCatch with argument B.[[Value]]). - Else, let C be B.
- Let F be
Completion (Evaluation ofFinally ). - If F is a
normal completion , set F to C. - Return ?
UpdateEmpty (F,undefined ).
14.16 The debugger Statement
Syntax
14.16.1 Runtime Semantics: Evaluation
Evaluating a
- If an
implementation-defined debugging facility is available and enabled, then- Perform an
implementation-defined debugging action. - Return a new
implementation-defined Completion Record .
- Perform an
- Else,
- Return
empty .
- Return
15 ECMAScript Language: Functions and Classes
Various ECMAScript language elements cause the creation of ECMAScript
15.1 Parameter Lists
Syntax
15.1.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
BoundNames ofFormalParameters contains any duplicate elements.
-
It is a Syntax Error if
IsSimpleParameterList ofFormalParameterList isfalse and theBoundNames ofFormalParameterList contains any duplicate elements.
Multiple occurrences of the same
15.1.2 Static Semantics: ContainsExpression
The
- Return
false .
- Return
ContainsExpression ofBindingPropertyList .
- Return
false .
- Return
ContainsExpression ofBindingRestElement .
- Return
ContainsExpression ofBindingElementList .
- Let has be
ContainsExpression ofBindingElementList . - If has is
true , returntrue . - Return
ContainsExpression ofBindingRestElement .
- Let has be
ContainsExpression ofBindingPropertyList . - If has is
true , returntrue . - Return
ContainsExpression ofBindingProperty .
- Let has be
ContainsExpression ofBindingElementList . - If has is
true , returntrue . - Return
ContainsExpression ofBindingElisionElement .
- Return
ContainsExpression ofBindingElement .
- Let has be
IsComputedPropertyKey ofPropertyName . - If has is
true , returntrue . - Return
ContainsExpression ofBindingElement .
- Return
true .
- Return
false .
- Return
true .
- Return
false .
- Return
ContainsExpression ofBindingPattern .
- Return
false .
- If
ContainsExpression ofFormalParameterList istrue , returntrue . - Return
ContainsExpression ofFunctionRestParameter .
- If
ContainsExpression ofFormalParameterList istrue , returntrue . - Return
ContainsExpression ofFormalParameter .
- Return
false .
- Let formals be the
ArrowFormalParameters that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return
ContainsExpression of formals.
- Return
false .
15.1.3 Static Semantics: IsSimpleParameterList
The
- Return
false .
- Return
false .
- Return
true .
- Return
false .
- Return
true .
- Return
false .
- Return
false .
- If
IsSimpleParameterList ofFormalParameterList isfalse , returnfalse . - Return
IsSimpleParameterList ofFormalParameter .
- Return
IsSimpleParameterList ofBindingElement .
- Return
true .
- Let formals be the
ArrowFormalParameters that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return
IsSimpleParameterList of formals.
- Return
true .
- Let head be the
AsyncArrowHead that iscovered byCoverCallExpressionAndAsyncArrowHead . - Return
IsSimpleParameterList of head.
15.1.4 Static Semantics: HasInitializer
The
- Return
false .
- Return
true .
- Return
false .
- Return
true .
- If
HasInitializer ofFormalParameterList istrue , returntrue . - Return
HasInitializer ofFormalParameter .
15.1.5 Static Semantics: ExpectedArgumentCount
The
- Return 0.
- Return the
ExpectedArgumentCount ofFormalParameterList .
The ExpectedArgumentCount of a
- If
HasInitializer ofFormalParameter istrue , return 0. - Return 1.
- Let count be the
ExpectedArgumentCount ofFormalParameterList . - If
HasInitializer ofFormalParameterList istrue orHasInitializer ofFormalParameter istrue , return count. - Return count + 1.
- Return 1.
- Let formals be the
ArrowFormalParameters that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return the
ExpectedArgumentCount of formals.
- If
HasInitializer ofFormalParameter istrue , return 0. - Return 1.
- Return 1.
15.2 Function Definitions
Syntax
15.2.1 Static Semantics: Early Errors
-
If
IsStrict (FormalParameters ) istrue , the Early Error rules forUniqueFormalParameters : FormalParameters -
If
BindingIdentifier is present andIsStrict (BindingIdentifier ) istrue , it is a Syntax Error if theStringValue ofBindingIdentifier is either"eval" or"arguments" . -
It is a Syntax Error if
FunctionBodyContainsUseStrict ofFunctionBody istrue andIsSimpleParameterList ofFormalParameters isfalse . -
It is a Syntax Error if any element of the
BoundNames ofFormalParameters also occurs in theLexicallyDeclaredNames ofFunctionBody . -
It is a Syntax Error if
FormalParameters Contains SuperProperty istrue . -
It is a Syntax Error if
FunctionBody Contains SuperProperty istrue . -
It is a Syntax Error if
FormalParameters Contains SuperCall istrue . -
It is a Syntax Error if
FunctionBody Contains SuperCall istrue .
The
-
It is a Syntax Error if the
LexicallyDeclaredNames ofFunctionStatementList contains any duplicate entries. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofFunctionStatementList also occurs in theVarDeclaredNames ofFunctionStatementList . -
It is a Syntax Error if
ContainsDuplicateLabels ofFunctionStatementList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedBreakTarget ofFunctionStatementList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedContinueTarget ofFunctionStatementList with arguments « » and « » istrue .
15.2.2 Static Semantics: FunctionBodyContainsUseStrict
The
- If the
Directive Prologue ofFunctionBody contains aUse Strict Directive , returntrue ; otherwise, returnfalse .
15.2.3 Runtime Semantics: EvaluateFunctionBody
The
- Perform ?
FunctionDeclarationInstantiation (functionObject, argumentsList). - Perform ?
Evaluation ofFunctionStatementList . - NOTE: If the previous step resulted in a
normal completion , then evaluation finished by proceeding past the end of theFunctionStatementList . - Return
ReturnCompletion (undefined ).
15.2.4 Runtime Semantics: InstantiateOrdinaryFunctionObject
The
- Let name be the
StringValue ofBindingIdentifier . - Let sourceText be the
source text matched by FunctionDeclaration . - Let F be
OrdinaryFunctionCreate (%Function.prototype% , sourceText,FormalParameters ,FunctionBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F, name). - Perform
MakeConstructor (F). - Return F.
- Let sourceText be the
source text matched by FunctionDeclaration . - Let F be
OrdinaryFunctionCreate (%Function.prototype% , sourceText,FormalParameters ,FunctionBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F,"default" ). - Perform
MakeConstructor (F). - Return F.
An anonymous export default declaration, and its function code is therefore always
15.2.5 Runtime Semantics: InstantiateOrdinaryFunctionExpression
The
- If name is not present, set name to
"" . - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by FunctionExpression . - Let closure be
OrdinaryFunctionCreate (%Function.prototype% , sourceText,FormalParameters ,FunctionBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (closure, name). - Perform
MakeConstructor (closure). - Return closure.
Assert : name is not present.- Set name to the
StringValue ofBindingIdentifier . - Let outerEnv be the
running execution context 's LexicalEnvironment. - Let funcEnv be
NewDeclarativeEnvironment (outerEnv). - Perform ! funcEnv.CreateImmutableBinding(name,
false ). - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by FunctionExpression . - Let closure be
OrdinaryFunctionCreate (%Function.prototype% , sourceText,FormalParameters ,FunctionBody ,non-lexical-this , funcEnv, privateEnv). - Perform
SetFunctionName (closure, name). - Perform
MakeConstructor (closure). - Perform ! funcEnv.InitializeBinding(name, closure).
- Return closure.
The
15.2.6 Runtime Semantics: Evaluation
- Return
empty .
An alternative semantics is provided in
- Return
empty .
A
- Return
undefined .
15.3 Arrow Function Definitions
Syntax
Supplemental Syntax
When processing an instance of the production
the interpretation of
15.3.1 Static Semantics: Early Errors
-
It is a Syntax Error if
ArrowParameters Contains YieldExpression istrue . -
It is a Syntax Error if
ArrowParameters Contains AwaitExpression istrue . -
It is a Syntax Error if
ConciseBodyContainsUseStrict ofConciseBody istrue andIsSimpleParameterList ofArrowParameters isfalse . -
It is a Syntax Error if any element of the
BoundNames ofArrowParameters also occurs in theLexicallyDeclaredNames ofConciseBody .
15.3.2 Static Semantics: ConciseBodyContainsUseStrict
The
- Return
false .
- Return
FunctionBodyContainsUseStrict ofFunctionBody .
15.3.3 Runtime Semantics: EvaluateConciseBody
The
- Perform ?
FunctionDeclarationInstantiation (functionObject, argumentsList). - Return ?
Evaluation ofExpressionBody .
15.3.4 Runtime Semantics: InstantiateArrowFunctionExpression
The
- If name is not present, set name to
"" . - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by ArrowFunction . - Let closure be
OrdinaryFunctionCreate (%Function.prototype% , sourceText,ArrowParameters ,ConciseBody ,lexical-this , env, privateEnv). - Perform
SetFunctionName (closure, name). - Return closure.
An arguments, super, this, or new.target. Any reference to arguments, super, this, or new.target within an super, the super is always contained within a non-super is accessible via the env that is captured by the
15.3.5 Runtime Semantics: Evaluation
- Return
InstantiateArrowFunctionExpression ofArrowFunction .
- Let exprRef be ?
Evaluation ofAssignmentExpression . - Let exprValue be ?
GetValue (exprRef). - Return
ReturnCompletion (exprValue).
15.4 Method Definitions
Syntax
15.4.1 Static Semantics: Early Errors
-
It is a Syntax Error if
FunctionBodyContainsUseStrict ofFunctionBody istrue andIsSimpleParameterList ofUniqueFormalParameters isfalse . -
It is a Syntax Error if any element of the
BoundNames ofUniqueFormalParameters also occurs in theLexicallyDeclaredNames ofFunctionBody .
-
It is a Syntax Error if the
BoundNames ofPropertySetParameterList contains any duplicate elements. -
It is a Syntax Error if
FunctionBodyContainsUseStrict ofFunctionBody istrue andIsSimpleParameterList ofPropertySetParameterList isfalse . -
It is a Syntax Error if any element of the
BoundNames ofPropertySetParameterList also occurs in theLexicallyDeclaredNames ofFunctionBody .
15.4.2 Static Semantics: HasDirectSuper
The
- If
UniqueFormalParameters Contains SuperCall istrue , returntrue . - Return
FunctionBody Contains SuperCall .
- Return
FunctionBody Contains SuperCall .
- If
PropertySetParameterList Contains SuperCall istrue , returntrue . - Return
FunctionBody Contains SuperCall .
- If
UniqueFormalParameters Contains SuperCall istrue , returntrue . - Return
GeneratorBody Contains SuperCall .
- If
UniqueFormalParameters Contains SuperCall istrue , returntrue . - Return
AsyncGeneratorBody Contains SuperCall .
- If
UniqueFormalParameters Contains SuperCall istrue , returntrue . - Return
AsyncFunctionBody Contains SuperCall .
15.4.3 Static Semantics: SpecialMethod
The
- Return
false .
- Return
true .
15.4.4 Runtime Semantics: DefineMethod
The
- Let propKey be ?
Evaluation ofClassElementName . - Let env be the
running execution context 's LexicalEnvironment. - Let privateEnv be the
running execution context 's PrivateEnvironment. - If functionPrototype is present, then
- Let prototype be functionPrototype.
- Else,
- Let prototype be
%Function.prototype% .
- Let prototype be
- Let sourceText be the
source text matched by MethodDefinition . - Let closure be
OrdinaryFunctionCreate (prototype, sourceText,UniqueFormalParameters ,FunctionBody ,non-lexical-this , env, privateEnv). - Perform
MakeMethod (closure, object). - Return the
Record { [[Key]]: propKey, [[Closure]]: closure }.
15.4.5 Runtime Semantics: MethodDefinitionEvaluation
The
- Let methodDef be ?
DefineMethod ofMethodDefinition with argument object. - Perform
SetFunctionName (methodDef.[[Closure]], methodDef.[[Key]]). - Return ?
DefineMethodProperty (object, methodDef.[[Key]], methodDef.[[Closure]], enumerable).
- Let propKey be ?
Evaluation ofClassElementName . - Let env be the
running execution context 's LexicalEnvironment. - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by MethodDefinition . - Let formalParameterList be an instance of the production
FormalParameters : [empty] - Let closure be
OrdinaryFunctionCreate (%Function.prototype% , sourceText, formalParameterList,FunctionBody ,non-lexical-this , env, privateEnv). - Perform
MakeMethod (closure, object). - Perform
SetFunctionName (closure, propKey,"get" ). - If propKey is a
Private Name , then- Return
PrivateElement { [[Key]]: propKey, [[Kind]]:accessor , [[Get]]: closure, [[Set]]:undefined }.
- Return
- Else,
- Let desc be the PropertyDescriptor { [[Get]]: closure, [[Enumerable]]: enumerable, [[Configurable]]:
true }. - Perform ?
DefinePropertyOrThrow (object, propKey, desc). - Return
unused .
- Let desc be the PropertyDescriptor { [[Get]]: closure, [[Enumerable]]: enumerable, [[Configurable]]:
- Let propKey be ?
Evaluation ofClassElementName . - Let env be the
running execution context 's LexicalEnvironment. - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by MethodDefinition . - Let closure be
OrdinaryFunctionCreate (%Function.prototype% , sourceText,PropertySetParameterList ,FunctionBody ,non-lexical-this , env, privateEnv). - Perform
MakeMethod (closure, object). - Perform
SetFunctionName (closure, propKey,"set" ). - If propKey is a
Private Name , then- Return
PrivateElement { [[Key]]: propKey, [[Kind]]:accessor , [[Get]]:undefined , [[Set]]: closure }.
- Return
- Else,
- Let desc be the PropertyDescriptor { [[Set]]: closure, [[Enumerable]]: enumerable, [[Configurable]]:
true }. - Perform ?
DefinePropertyOrThrow (object, propKey, desc). - Return
unused .
- Let desc be the PropertyDescriptor { [[Set]]: closure, [[Enumerable]]: enumerable, [[Configurable]]:
- Let propKey be ?
Evaluation ofClassElementName . - Let env be the
running execution context 's LexicalEnvironment. - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by GeneratorMethod . - Let closure be
OrdinaryFunctionCreate (%GeneratorFunction.prototype% , sourceText,UniqueFormalParameters ,GeneratorBody ,non-lexical-this , env, privateEnv). - Perform
MakeMethod (closure, object). - Perform
SetFunctionName (closure, propKey). - Let prototype be
OrdinaryObjectCreate (%GeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return ?
DefineMethodProperty (object, propKey, closure, enumerable).
- Let propKey be ?
Evaluation ofClassElementName . - Let env be the
running execution context 's LexicalEnvironment. - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by AsyncGeneratorMethod . - Let closure be
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% , sourceText,UniqueFormalParameters ,AsyncGeneratorBody ,non-lexical-this , env, privateEnv). - Perform
MakeMethod (closure, object). - Perform
SetFunctionName (closure, propKey). - Let prototype be
OrdinaryObjectCreate (%AsyncGeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return ?
DefineMethodProperty (object, propKey, closure, enumerable).
- Let propKey be ?
Evaluation ofClassElementName . - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by AsyncMethod . - Let closure be
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText,UniqueFormalParameters ,AsyncFunctionBody ,non-lexical-this , env, privateEnv). - Perform
MakeMethod (closure, object). - Perform
SetFunctionName (closure, propKey). - Return ?
DefineMethodProperty (object, propKey, closure, enumerable).
15.5 Generator Function Definitions
Syntax
The syntactic context immediately following yield requires use of the
15.5.1 Static Semantics: Early Errors
-
It is a Syntax Error if
HasDirectSuper ofGeneratorMethod istrue . -
It is a Syntax Error if
UniqueFormalParameters Contains YieldExpression istrue . -
It is a Syntax Error if
FunctionBodyContainsUseStrict ofGeneratorBody istrue andIsSimpleParameterList ofUniqueFormalParameters isfalse . -
It is a Syntax Error if any element of the
BoundNames ofUniqueFormalParameters also occurs in theLexicallyDeclaredNames ofGeneratorBody .
-
If
IsStrict (FormalParameters ) istrue , the Early Error rules forUniqueFormalParameters : FormalParameters -
If
BindingIdentifier is present andIsStrict (BindingIdentifier ) istrue , it is a Syntax Error if theStringValue ofBindingIdentifier is either"eval" or"arguments" . -
It is a Syntax Error if
FunctionBodyContainsUseStrict ofGeneratorBody istrue andIsSimpleParameterList ofFormalParameters isfalse . -
It is a Syntax Error if any element of the
BoundNames ofFormalParameters also occurs in theLexicallyDeclaredNames ofGeneratorBody . -
It is a Syntax Error if
FormalParameters Contains YieldExpression istrue . -
It is a Syntax Error if
FormalParameters Contains SuperProperty istrue . -
It is a Syntax Error if
GeneratorBody Contains SuperProperty istrue . -
It is a Syntax Error if
FormalParameters Contains SuperCall istrue . -
It is a Syntax Error if
GeneratorBody Contains SuperCall istrue .
15.5.2 Runtime Semantics: EvaluateGeneratorBody
The
- Perform ?
FunctionDeclarationInstantiation (functionObject, argumentsList). - Let G be ?
OrdinaryCreateFromConstructor (functionObject,"%GeneratorPrototype%" , « [[GeneratorState]], [[GeneratorContext]], [[GeneratorBrand]] »). - Set G.[[GeneratorBrand]] to
empty . - Set G.[[GeneratorState]] to
suspended-start . - Perform
GeneratorStart (G,FunctionBody ). - Return
ReturnCompletion (G).
15.5.3 Runtime Semantics: InstantiateGeneratorFunctionObject
The
- Let name be the
StringValue ofBindingIdentifier . - Let sourceText be the
source text matched by GeneratorDeclaration . - Let F be
OrdinaryFunctionCreate (%GeneratorFunction.prototype% , sourceText,FormalParameters ,GeneratorBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F, name). - Let prototype be
OrdinaryObjectCreate (%GeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return F.
- Let sourceText be the
source text matched by GeneratorDeclaration . - Let F be
OrdinaryFunctionCreate (%GeneratorFunction.prototype% , sourceText,FormalParameters ,GeneratorBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F,"default" ). - Let prototype be
OrdinaryObjectCreate (%GeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return F.
An anonymous export default declaration, and its function code is therefore always
15.5.4 Runtime Semantics: InstantiateGeneratorFunctionExpression
The
- If name is not present, set name to
"" . - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by GeneratorExpression . - Let closure be
OrdinaryFunctionCreate (%GeneratorFunction.prototype% , sourceText,FormalParameters ,GeneratorBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (closure, name). - Let prototype be
OrdinaryObjectCreate (%GeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return closure.
Assert : name is not present.- Set name to the
StringValue ofBindingIdentifier . - Let outerEnv be the
running execution context 's LexicalEnvironment. - Let funcEnv be
NewDeclarativeEnvironment (outerEnv). - Perform ! funcEnv.CreateImmutableBinding(name,
false ). - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by GeneratorExpression . - Let closure be
OrdinaryFunctionCreate (%GeneratorFunction.prototype% , sourceText,FormalParameters ,GeneratorBody ,non-lexical-this , funcEnv, privateEnv). - Perform
SetFunctionName (closure, name). - Let prototype be
OrdinaryObjectCreate (%GeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Perform ! funcEnv.InitializeBinding(name, closure).
- Return closure.
The
15.5.5 Runtime Semantics: Evaluation
- Return ?
Yield (undefined ).
- Let exprRef be ?
Evaluation ofAssignmentExpression . - Let value be ?
GetValue (exprRef). - Return ?
Yield (value).
- Let generatorKind be
GetGeneratorKind (). Assert : generatorKind is eithersync orasync .- Let exprRef be ?
Evaluation ofAssignmentExpression . - Let value be ?
GetValue (exprRef). - Let iteratorRecord be ?
GetIterator (value, generatorKind). - Let iterator be iteratorRecord.[[Iterator]].
- Let received be
NormalCompletion (undefined ). - Repeat,
- If received is a
normal completion , then- Let innerResult be ?
Call (iteratorRecord.[[NextMethod]], iteratorRecord.[[Iterator]], « received.[[Value]] »). - If generatorKind is
async , set innerResult to ?Await (innerResult). - If innerResult
is not an Object , throw aTypeError exception. - Let done be ?
IteratorComplete (innerResult). - If done is
true , then- Return ?
IteratorValue (innerResult).
- Return ?
- If generatorKind is
async , set received toCompletion (AsyncGeneratorYield (?IteratorValue (innerResult))). - Else, set received to
Completion (GeneratorYield (innerResult)).
- Let innerResult be ?
- Else if received is a
throw completion , then- Let throw be ?
GetMethod (iterator,"throw" ). - If throw is not
undefined , then- Let innerResult be ?
Call (throw, iterator, « received.[[Value]] »). - If generatorKind is
async , set innerResult to ?Await (innerResult). - NOTE: Exceptions from the inner
iterator throwmethod are propagated.Normal completions from an innerthrowmethod are processed similarly to an innernext. - If innerResult
is not an Object , throw aTypeError exception. - Let done be ?
IteratorComplete (innerResult). - If done is
true , then- Return ?
IteratorValue (innerResult).
- Return ?
- If generatorKind is
async , set received toCompletion (AsyncGeneratorYield (?IteratorValue (innerResult))). - Else, set received to
Completion (GeneratorYield (innerResult)).
- Let innerResult be ?
- Else,
- NOTE: If iterator does not have a
throwmethod, this throw is going to terminate theyield*loop. But first we need to give iterator a chance to clean up. - Let closeCompletion be
NormalCompletion (empty ). - If generatorKind is
async , perform ?AsyncIteratorClose (iteratorRecord, closeCompletion). - Else, perform ?
IteratorClose (iteratorRecord, closeCompletion). - NOTE: The next step throws a
TypeError to indicate that there was ayield*protocol violation: iterator does not have athrowmethod. - Throw a
TypeError exception.
- NOTE: If iterator does not have a
- Let throw be ?
- Else,
Assert : received is areturn completion .- Let return be ?
GetMethod (iterator,"return" ). - If return is
undefined , then- Set value to received.[[Value]].
- If generatorKind is
async , then- Set value to ?
Await (value).
- Set value to ?
- Return
ReturnCompletion (value).
- Let innerReturnResult be ?
Call (return, iterator, « received.[[Value]] »). - If generatorKind is
async , set innerReturnResult to ?Await (innerReturnResult). - If innerReturnResult
is not an Object , throw aTypeError exception. - Let done be ?
IteratorComplete (innerReturnResult). - If done is
true , then- Set value to ?
IteratorValue (innerReturnResult). - Return
ReturnCompletion (value).
- Set value to ?
- If generatorKind is
async , set received toCompletion (AsyncGeneratorYield (?IteratorValue (innerReturnResult))). - Else, set received to
Completion (GeneratorYield (innerReturnResult)).
- If received is a
15.6 Async Generator Function Definitions
Syntax
15.6.1 Static Semantics: Early Errors
- It is a Syntax Error if
HasDirectSuper ofAsyncGeneratorMethod istrue . - It is a Syntax Error if
UniqueFormalParameters Contains YieldExpression istrue . - It is a Syntax Error if
UniqueFormalParameters Contains AwaitExpression istrue . - It is a Syntax Error if
FunctionBodyContainsUseStrict ofAsyncGeneratorBody istrue andIsSimpleParameterList ofUniqueFormalParameters isfalse . - It is a Syntax Error if any element of the
BoundNames ofUniqueFormalParameters also occurs in theLexicallyDeclaredNames ofAsyncGeneratorBody .
- If
IsStrict (FormalParameters ) istrue , the Early Error rules forUniqueFormalParameters : FormalParameters - If
BindingIdentifier is present andIsStrict (BindingIdentifier ) istrue , it is a Syntax Error if theStringValue ofBindingIdentifier is either"eval" or"arguments" . - It is a Syntax Error if
FunctionBodyContainsUseStrict ofAsyncGeneratorBody istrue andIsSimpleParameterList ofFormalParameters isfalse . - It is a Syntax Error if any element of the
BoundNames ofFormalParameters also occurs in theLexicallyDeclaredNames ofAsyncGeneratorBody . - It is a Syntax Error if
FormalParameters Contains YieldExpression istrue . - It is a Syntax Error if
FormalParameters Contains AwaitExpression istrue . - It is a Syntax Error if
FormalParameters Contains SuperProperty istrue . - It is a Syntax Error if
AsyncGeneratorBody Contains SuperProperty istrue . - It is a Syntax Error if
FormalParameters Contains SuperCall istrue . - It is a Syntax Error if
AsyncGeneratorBody Contains SuperCall istrue .
15.6.2 Runtime Semantics: EvaluateAsyncGeneratorBody
The
- Perform ?
FunctionDeclarationInstantiation (functionObject, argumentsList). - Let generator be ?
OrdinaryCreateFromConstructor (functionObject,"%AsyncGeneratorPrototype%" , « [[AsyncGeneratorState]], [[AsyncGeneratorContext]], [[AsyncGeneratorQueue]], [[GeneratorBrand]] »). - Set generator.[[GeneratorBrand]] to
empty . - Set generator.[[AsyncGeneratorState]] to
suspended-start . - Perform
AsyncGeneratorStart (generator,FunctionBody ). - Return
ReturnCompletion (generator).
15.6.3 Runtime Semantics: InstantiateAsyncGeneratorFunctionObject
The
- Let name be the
StringValue ofBindingIdentifier . - Let sourceText be the
source text matched by AsyncGeneratorDeclaration . - Let F be
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% , sourceText,FormalParameters ,AsyncGeneratorBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F, name). - Let prototype be
OrdinaryObjectCreate (%AsyncGeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return F.
- Let sourceText be the
source text matched by AsyncGeneratorDeclaration . - Let F be
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% , sourceText,FormalParameters ,AsyncGeneratorBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F,"default" ). - Let prototype be
OrdinaryObjectCreate (%AsyncGeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return F.
An anonymous export default declaration.
15.6.4 Runtime Semantics: InstantiateAsyncGeneratorFunctionExpression
The
- If name is not present, set name to
"" . - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by AsyncGeneratorExpression . - Let closure be
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% , sourceText,FormalParameters ,AsyncGeneratorBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (closure, name). - Let prototype be
OrdinaryObjectCreate (%AsyncGeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Return closure.
Assert : name is not present.- Set name to the
StringValue ofBindingIdentifier . - Let outerEnv be the
running execution context 's LexicalEnvironment. - Let funcEnv be
NewDeclarativeEnvironment (outerEnv). - Perform ! funcEnv.CreateImmutableBinding(name,
false ). - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by AsyncGeneratorExpression . - Let closure be
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% , sourceText,FormalParameters ,AsyncGeneratorBody ,non-lexical-this , funcEnv, privateEnv). - Perform
SetFunctionName (closure, name). - Let prototype be
OrdinaryObjectCreate (%AsyncGeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }). - Perform ! funcEnv.InitializeBinding(name, closure).
- Return closure.
The
15.6.5 Runtime Semantics: Evaluation
15.7 Class Definitions
Syntax
A class definition is always
15.7.1 Static Semantics: Early Errors
-
It is a Syntax Error if
ClassHeritage is not present and the following algorithm returnstrue :- Let constructor be the
ConstructorMethod ofClassBody . - If constructor is
empty , returnfalse . - Return
HasDirectSuper of constructor.
- Let constructor be the
-
It is a Syntax Error if the
PrototypePropertyNameList ofClassElementList contains more than one occurrence of"constructor" . -
It is a Syntax Error if the
PrivateBoundIdentifiers ofClassElementList contains any duplicate entries, unless the name is used once for a getter and once for a setter and in no other entries, and the getter and setter are either both static or both non-static.
-
It is a Syntax Error if the
PropName ofMethodDefinition is not"constructor" andHasDirectSuper ofMethodDefinition istrue . -
It is a Syntax Error if the
PropName ofMethodDefinition is"constructor" andSpecialMethod ofMethodDefinition istrue .
-
It is a Syntax Error if
HasDirectSuper ofMethodDefinition istrue . -
It is a Syntax Error if the
PropName ofMethodDefinition is"prototype" .
- It is a Syntax Error if the
PropName ofFieldDefinition is"constructor" .
-
It is a Syntax Error if the
PropName ofFieldDefinition is either"prototype" or"constructor" .
- It is a Syntax Error if
Initializer is present andContainsArguments ofInitializer istrue . - It is a Syntax Error if
Initializer is present andInitializer Contains SuperCall istrue .
- It is a Syntax Error if the
StringValue ofPrivateIdentifier is"#constructor" .
-
It is a Syntax Error if the
LexicallyDeclaredNames ofClassStaticBlockStatementList contains any duplicate entries. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofClassStaticBlockStatementList also occurs in theVarDeclaredNames ofClassStaticBlockStatementList . -
It is a Syntax Error if
ContainsDuplicateLabels ofClassStaticBlockStatementList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedBreakTarget ofClassStaticBlockStatementList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedContinueTarget ofClassStaticBlockStatementList with arguments « » and « » istrue . -
It is a Syntax Error if
ContainsArguments ofClassStaticBlockStatementList istrue . -
It is a Syntax Error if
ClassStaticBlockStatementList Contains SuperCall istrue . -
It is a Syntax Error if
ClassStaticBlockStatementList Contains awaitistrue .
15.7.2 Static Semantics: ClassElementKind
The
- If the
PropName ofMethodDefinition is"constructor" , returnconstructor-method . - Return
non-constructor-method .
- Return
non-constructor-method .
- Return
non-constructor-method .
- Return
empty .
15.7.3 Static Semantics: ConstructorMethod
The
- If the
ClassElementKind ofClassElement isconstructor-method , returnClassElement . - Return
empty .
- Let head be the
ConstructorMethod ofClassElementList . - If head is not
empty , return head. - If the
ClassElementKind ofClassElement isconstructor-method , returnClassElement . - Return
empty .
Early Error rules ensure that there is only one method definition named
15.7.4 Static Semantics: IsStatic
The
- Return
false .
- Return
true .
- Return
false .
- Return
true .
- Return
true .
- Return
false .
15.7.5 Static Semantics: NonConstructorElements
The
- If the
ClassElementKind ofClassElement isnon-constructor-method , then- Return «
ClassElement ».
- Return «
- Return a new empty
List .
- Let list be the
NonConstructorElements ofClassElementList . - If the
ClassElementKind ofClassElement isnon-constructor-method , then- Append
ClassElement to the end of list.
- Append
- Return list.
15.7.6 Static Semantics: PrototypePropertyNameList
The
- Let propName be the
PropName ofClassElement . - If propName is
empty , return a new emptyList . - If
IsStatic ofClassElement istrue , return a new emptyList . - Return « propName ».
- Let list be the
PrototypePropertyNameList ofClassElementList . - Let propName be the
PropName ofClassElement . - If propName is
empty , return list. - If
IsStatic ofClassElement istrue , return list. - Return the
list-concatenation of list and « propName ».
15.7.7 Static Semantics: AllPrivateIdentifiersValid
The
Every grammar production alternative in this specification which is not listed below implicitly has the following default definition of AllPrivateIdentifiersValid:
- For each child node child of this
Parse Node , do- If child is an instance of a nonterminal, then
- If
AllPrivateIdentifiersValid of child with argument names isfalse , returnfalse .
- If
- If child is an instance of a nonterminal, then
- Return
true .
- If names contains the
StringValue ofPrivateIdentifier , then- Return
AllPrivateIdentifiersValid ofMemberExpression with argument names.
- Return
- Return
false .
- If names contains the
StringValue ofPrivateIdentifier , then- Return
AllPrivateIdentifiersValid ofCallExpression with argument names.
- Return
- Return
false .
- If names contains the
StringValue ofPrivateIdentifier , returntrue . - Return
false .
- If names contains the
StringValue ofPrivateIdentifier , then- Return
AllPrivateIdentifiersValid ofOptionalChain with argument names.
- Return
- Return
false .
- Let newNames be the
list-concatenation of names and thePrivateBoundIdentifiers ofClassBody . - Return
AllPrivateIdentifiersValid ofClassElementList with argument newNames.
- If names contains the
StringValue ofPrivateIdentifier , then- Return
AllPrivateIdentifiersValid ofShiftExpression with argument names.
- Return
- Return
false .
15.7.8 Static Semantics: PrivateBoundIdentifiers
The
- Return the
PrivateBoundIdentifiers ofClassElementName .
- Return a
List whose sole element is theStringValue ofPrivateIdentifier .
- Return a new empty
List .
- Let names1 be the
PrivateBoundIdentifiers ofClassElementList . - Let names2 be the
PrivateBoundIdentifiers ofClassElement . - Return the
list-concatenation of names1 and names2.
- Return the
PrivateBoundIdentifiers ofClassElementName .
15.7.9 Static Semantics: ContainsArguments
The
Every grammar production alternative in this specification which is not listed below implicitly has the following default definition of ContainsArguments:
- For each child node child of this
Parse Node , do- If child is an instance of a nonterminal, then
- If
ContainsArguments of child istrue , returntrue .
- If
- If child is an instance of a nonterminal, then
- Return
false .
- If the
StringValue ofIdentifier is"arguments" , returntrue . - Return
false .
- Return
false .
- Return
ContainsArguments ofClassElementName .
15.7.10 Runtime Semantics: ClassFieldDefinitionEvaluation
The
- Let name be ?
Evaluation ofClassElementName . - If
Initializer is present, then- Let formalParameterList be an instance of the production
FormalParameters : [empty] - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the empty sequence of Unicode code points.
- Let initializer be
OrdinaryFunctionCreate (%Function.prototype% , sourceText, formalParameterList,Initializer ,non-lexical-this , env, privateEnv). - Perform
MakeMethod (initializer, homeObject). - Set initializer.[[ClassFieldInitializerName]] to name.
- Let formalParameterList be an instance of the production
- Else,
- Let initializer be
empty .
- Let initializer be
- Return the
ClassFieldDefinition Record { [[Name]]: name, [[Initializer]]: initializer }.
15.7.11 Runtime Semantics: ClassStaticBlockDefinitionEvaluation
The
- Let lex be the
running execution context 's LexicalEnvironment. - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the empty sequence of Unicode code points.
- Let formalParameters be an instance of the production
FormalParameters : [empty] - Let bodyFunction be
OrdinaryFunctionCreate (%Function.prototype% , sourceText, formalParameters,ClassStaticBlockBody ,non-lexical-this , lex, privateEnv). - Perform
MakeMethod (bodyFunction, homeObject). - Return the
ClassStaticBlockDefinition Record { [[BodyFunction]]: bodyFunction }.
15.7.12 Runtime Semantics: EvaluateClassStaticBlockBody
The
Assert : functionObject is a synthetic function created byClassStaticBlockDefinitionEvaluation step5 .- Perform !
FunctionDeclarationInstantiation (functionObject, « »). - Perform ?
Evaluation ofClassStaticBlockStatementList . - Return
ReturnCompletion (undefined ).
15.7.13 Runtime Semantics: ClassElementEvaluation
The
- Return ?
ClassFieldDefinitionEvaluation ofFieldDefinition with argument object.
- Return ?
MethodDefinitionEvaluation ofMethodDefinition with arguments object andfalse .
- Return the
ClassStaticBlockDefinitionEvaluation ofClassStaticBlock with argument object.
- Return
unused .
15.7.14 Runtime Semantics: ClassDefinitionEvaluation
The
For ease of specification, private methods and accessors are included alongside private fields in the [[PrivateElements]] slot of class instances. However, any given object has either all or none of the private methods and accessors defined by a given class. This feature has been designed so that implementations may choose to implement private methods and accessors using a strategy which does not require tracking each method or accessor individually.
For example, an implementation could directly associate instance private methods with their corresponding this value. Looking up an instance private method on an object then consists of checking that the class
This differs from private fields: because field initializers can throw during class instantiation, an individual object may have some proper subset of the private fields of a given class, and so private fields must in general be tracked individually.
It is defined piecewise over the following productions:
- Let env be the LexicalEnvironment of the
running execution context . - Let classEnv be
NewDeclarativeEnvironment (env). - If classBinding is not
undefined , then- Perform ! classEnv.CreateImmutableBinding(classBinding,
true ).
- Perform ! classEnv.CreateImmutableBinding(classBinding,
- Let outerPrivateEnvironment be the
running execution context 's PrivateEnvironment. - Let classPrivateEnvironment be
NewPrivateEnvironment (outerPrivateEnvironment). - If
ClassBody is present, then- For each String dn of the
PrivateBoundIdentifiers ofClassBody , do- If classPrivateEnvironment.[[Names]] contains a
Private Name pn such that pn.[[Description]] is dn, thenAssert : This is only possible for getter/setter pairs.
- Else,
- Let name be a new
Private Name whose [[Description]] is dn. - Append name to classPrivateEnvironment.[[Names]].
- Let name be a new
- If classPrivateEnvironment.[[Names]] contains a
- For each String dn of the
- If
ClassHeritage is not present, then- Let protoParent be
%Object.prototype% . - Let constructorParent be
%Function.prototype% .
- Let protoParent be
- Else,
- Set the
running execution context 's LexicalEnvironment to classEnv. - NOTE: The
running execution context 's PrivateEnvironment is outerPrivateEnvironment when evaluatingClassHeritage . - Let superclassRef be
Completion (Evaluation ofClassHeritage ). - Set the
running execution context 's LexicalEnvironment to env. - Let superclass be ?
GetValue (? superclassRef). - If superclass is
null , then- Let protoParent be
null . - Let constructorParent be
%Function.prototype% .
- Let protoParent be
- Else if
IsConstructor (superclass) isfalse , then- Throw a
TypeError exception.
- Throw a
- Else,
- Let protoParent be ?
Get (superclass,"prototype" ). - If protoParent
is not an Object and protoParent is notnull , throw aTypeError exception. - Let constructorParent be superclass.
- Let protoParent be ?
- Set the
- Let proto be
OrdinaryObjectCreate (protoParent). - If
ClassBody is not present, let constructor beempty . - Else, let constructor be the
ConstructorMethod ofClassBody . - Set the
running execution context 's LexicalEnvironment to classEnv. - Set the
running execution context 's PrivateEnvironment to classPrivateEnvironment. - If constructor is
empty , then- Let defaultConstructor be a new
Abstract Closure with no parameters that captures nothing and performs the following steps when called:- Let args be the
List of arguments that was passed to this function by [[Call]] or [[Construct]]. - If NewTarget is
undefined , throw aTypeError exception. - Let F be the
active function object . - If F.[[ConstructorKind]] is
derived , then- NOTE: This branch behaves similarly to
constructor(...args) { super(...args); }. The most notable distinction is that while the aforementionedECMAScript source text observably calls the%Symbol.iterator% method on%Array.prototype%, this function does not. - Let func be ! F.[[GetPrototypeOf]]().
- If
IsConstructor (func) isfalse , throw aTypeError exception. - Let result be ?
Construct (func, args, NewTarget).
- NOTE: This branch behaves similarly to
- Else,
- NOTE: This branch behaves similarly to
constructor() {}. - Let result be ?
OrdinaryCreateFromConstructor (NewTarget,"%Object.prototype%" ).
- NOTE: This branch behaves similarly to
- Perform ?
InitializeInstanceElements (result, F). - Return result.
- Let args be the
- Let F be
CreateBuiltinFunction (defaultConstructor, 0, className, « [[ConstructorKind]], [[SourceText]] »,the current Realm Record , constructorParent).
- Let defaultConstructor be a new
- Else,
- Let constructorInfo be !
DefineMethod of constructor with arguments proto and constructorParent. - Let F be constructorInfo.[[Closure]].
- Perform
MakeClassConstructor (F). - Perform
SetFunctionName (F, className).
- Let constructorInfo be !
- Perform
MakeConstructor (F,false , proto). - If
ClassHeritage is present, set F.[[ConstructorKind]] toderived . - Perform !
DefineMethodProperty (proto,"constructor" , F,false ). - If
ClassBody is not present, let elements be a new emptyList . - Else, let elements be the
NonConstructorElements ofClassBody . - Let instancePrivateMethods be a new empty
List . - Let staticPrivateMethods be a new empty
List . - Let instanceFields be a new empty
List . - Let staticElements be a new empty
List . - For each
ClassElement e of elements, do- If
IsStatic of e isfalse , then- Let element be
Completion (ClassElementEvaluation of e with argument proto).
- Let element be
- Else,
- Let element be
Completion (ClassElementEvaluation of e with argument F).
- Let element be
- If element is an
abrupt completion , then- Set the
running execution context 's LexicalEnvironment to env. - Set the
running execution context 's PrivateEnvironment to outerPrivateEnvironment. - Return ? element.
- Set the
- Set element to ! element.
- If element is a
PrivateElement , thenAssert : element.[[Kind]] is eithermethod oraccessor .- If
IsStatic of e isfalse , let container be instancePrivateMethods. - Else, let container be staticPrivateMethods.
- If container contains a
PrivateElement pe such that pe.[[Key]] is element.[[Key]], thenAssert : element.[[Kind]] and pe.[[Kind]] are bothaccessor .- If element.[[Get]] is
undefined , then- Let combined be
PrivateElement { [[Key]]: element.[[Key]], [[Kind]]:accessor , [[Get]]: pe.[[Get]], [[Set]]: element.[[Set]] }.
- Let combined be
- Else,
- Let combined be
PrivateElement { [[Key]]: element.[[Key]], [[Kind]]:accessor , [[Get]]: element.[[Get]], [[Set]]: pe.[[Set]] }.
- Let combined be
- Replace pe in container with combined.
- Else,
- Append element to container.
- Else if element is a
ClassFieldDefinition Record , then- If
IsStatic of e isfalse , append element to instanceFields. - Else, append element to staticElements.
- If
- Else if element is a
ClassStaticBlockDefinition Record , then- Append element to staticElements.
- If
- Set the
running execution context 's LexicalEnvironment to env. - If classBinding is not
undefined , then- Perform ! classEnv.InitializeBinding(classBinding, F).
- Set F.[[PrivateMethods]] to instancePrivateMethods.
- Set F.[[Fields]] to instanceFields.
- For each
PrivateElement method of staticPrivateMethods, do- Perform !
PrivateMethodOrAccessorAdd (F, method).
- Perform !
- For each element elementRecord of staticElements, do
- If elementRecord is a
ClassFieldDefinition Record , then- Let result be
Completion (DefineField (F, elementRecord)).
- Let result be
- Else,
Assert : elementRecord is aClassStaticBlockDefinition Record .- Let result be
Completion (Call (elementRecord.[[BodyFunction]], F)).
- If result is an
abrupt completion , then- Set the
running execution context 's PrivateEnvironment to outerPrivateEnvironment. - Return ? result.
- Set the
- If elementRecord is a
- Set the
running execution context 's PrivateEnvironment to outerPrivateEnvironment. - Return F.
15.7.15 Runtime Semantics: BindingClassDeclarationEvaluation
The
- Let className be the
StringValue ofBindingIdentifier . - Let value be ?
ClassDefinitionEvaluation ofClassTail with arguments className and className. - Set value.[[SourceText]] to the
source text matched by ClassDeclaration . - Let env be the
running execution context 's LexicalEnvironment. - Perform ?
InitializeBoundName (className, value, env). - Return value.
- Let value be ?
ClassDefinitionEvaluation ofClassTail with argumentsundefined and"default" . - Set value.[[SourceText]] to the
source text matched by ClassDeclaration . - Return value.
15.7.16 Runtime Semantics: Evaluation
- Perform ?
BindingClassDeclarationEvaluation of thisClassDeclaration . - Return
empty .
- Let value be ?
ClassDefinitionEvaluation ofClassTail with argumentsundefined and"" . - Set value.[[SourceText]] to the
source text matched by ClassExpression . - Return value.
- Let className be the
StringValue ofBindingIdentifier . - Let value be ?
ClassDefinitionEvaluation ofClassTail with arguments className and className. - Set value.[[SourceText]] to the
source text matched by ClassExpression . - Return value.
- Let privateIdentifier be the
StringValue ofPrivateIdentifier . - Let privateEnvRec be the
running execution context 's PrivateEnvironment. - Let names be privateEnvRec.[[Names]].
Assert : Exactly one element of names is aPrivate Name whose [[Description]] is privateIdentifier.- Let privateName be the
Private Name in names whose [[Description]] is privateIdentifier. - Return privateName.
- Return
undefined .
15.8 Async Function Definitions
Syntax
await is parsed as a
- In an
AsyncFunctionBody . - In the
FormalParameters of anAsyncFunctionDeclaration ,AsyncFunctionExpression ,AsyncGeneratorDeclaration , orAsyncGeneratorExpression .AwaitExpression in this position is a Syntax error viastatic semantics . - In a
Module .
When await may be parsed as an identifier when the [Await] parameter is absent. This includes the following contexts:
- Anywhere outside of an
AsyncFunctionBody orFormalParameters of anAsyncFunctionDeclaration ,AsyncFunctionExpression ,AsyncGeneratorDeclaration , orAsyncGeneratorExpression . - In the
BindingIdentifier of aFunctionExpression ,GeneratorExpression , orAsyncGeneratorExpression .
Unlike
15.8.1 Static Semantics: Early Errors
- It is a Syntax Error if
FunctionBodyContainsUseStrict ofAsyncFunctionBody istrue andIsSimpleParameterList ofUniqueFormalParameters isfalse . - It is a Syntax Error if
HasDirectSuper ofAsyncMethod istrue . - It is a Syntax Error if
UniqueFormalParameters Contains AwaitExpression istrue . - It is a Syntax Error if any element of the
BoundNames ofUniqueFormalParameters also occurs in theLexicallyDeclaredNames ofAsyncFunctionBody .
- It is a Syntax Error if
FunctionBodyContainsUseStrict ofAsyncFunctionBody istrue andIsSimpleParameterList ofFormalParameters isfalse . - It is a Syntax Error if
FormalParameters Contains AwaitExpression istrue . - If
IsStrict (FormalParameters ) istrue , the Early Error rules forUniqueFormalParameters : FormalParameters - If
BindingIdentifier is present andIsStrict (BindingIdentifier ) istrue , it is a Syntax Error if theStringValue ofBindingIdentifier is either"eval" or"arguments" . - It is a Syntax Error if any element of the
BoundNames ofFormalParameters also occurs in theLexicallyDeclaredNames ofAsyncFunctionBody . - It is a Syntax Error if
FormalParameters Contains SuperProperty istrue . - It is a Syntax Error if
AsyncFunctionBody Contains SuperProperty istrue . - It is a Syntax Error if
FormalParameters Contains SuperCall istrue . - It is a Syntax Error if
AsyncFunctionBody Contains SuperCall istrue .
15.8.2 Runtime Semantics: InstantiateAsyncFunctionObject
The
- Let name be the
StringValue ofBindingIdentifier . - Let sourceText be the
source text matched by AsyncFunctionDeclaration . - Let F be
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText,FormalParameters ,AsyncFunctionBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F, name). - Return F.
- Let sourceText be the
source text matched by AsyncFunctionDeclaration . - Let F be
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText,FormalParameters ,AsyncFunctionBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F,"default" ). - Return F.
15.8.3 Runtime Semantics: InstantiateAsyncFunctionExpression
The
- If name is not present, set name to
"" . - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by AsyncFunctionExpression . - Let closure be
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText,FormalParameters ,AsyncFunctionBody ,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (closure, name). - Return closure.
Assert : name is not present.- Set name to the
StringValue ofBindingIdentifier . - Let outerEnv be the LexicalEnvironment of the
running execution context . - Let funcEnv be
NewDeclarativeEnvironment (outerEnv). - Perform ! funcEnv.CreateImmutableBinding(name,
false ). - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by AsyncFunctionExpression . - Let closure be
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText,FormalParameters ,AsyncFunctionBody ,non-lexical-this , funcEnv, privateEnv). - Perform
SetFunctionName (closure, name). - Perform ! funcEnv.InitializeBinding(name, closure).
- Return closure.
The
15.8.4 Runtime Semantics: EvaluateAsyncFunctionBody
The
- Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let completion be
Completion (FunctionDeclarationInstantiation (functionObject, argumentsList)). - If completion is an
abrupt completion , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « completion.[[Value]] »).
- Perform !
- Else,
- Perform
AsyncFunctionStart (promiseCapability,FunctionBody ).
- Perform
- Return
ReturnCompletion (promiseCapability.[[Promise]]).
15.8.5 Runtime Semantics: Evaluation
- Let exprRef be ?
Evaluation ofUnaryExpression . - Let value be ?
GetValue (exprRef). - Return ?
Await (value).
15.9 Async Arrow Function Definitions
Syntax
Supplemental Syntax
When processing an instance of the production
the interpretation of
15.9.1 Static Semantics: Early Errors
- It is a Syntax Error if any element of the
BoundNames ofAsyncArrowBindingIdentifier also occurs in theLexicallyDeclaredNames ofAsyncConciseBody .
CoverCallExpressionAndAsyncArrowHead must cover anAsyncArrowHead .- It is a Syntax Error if
CoverCallExpressionAndAsyncArrowHead Contains YieldExpression istrue . - It is a Syntax Error if
CoverCallExpressionAndAsyncArrowHead Contains AwaitExpression istrue . - It is a Syntax Error if any element of the
BoundNames ofCoverCallExpressionAndAsyncArrowHead also occurs in theLexicallyDeclaredNames ofAsyncConciseBody . - It is a Syntax Error if
AsyncConciseBodyContainsUseStrict ofAsyncConciseBody istrue andIsSimpleParameterList ofCoverCallExpressionAndAsyncArrowHead isfalse .
15.9.2 Static Semantics: AsyncConciseBodyContainsUseStrict
The
- Return
false .
- Return
FunctionBodyContainsUseStrict ofAsyncFunctionBody .
15.9.3 Runtime Semantics: EvaluateAsyncConciseBody
The
- Let promiseCapability be !
NewPromiseCapability (%Promise% ). - Let completion be
Completion (FunctionDeclarationInstantiation (functionObject, argumentsList)). - If completion is an
abrupt completion , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « completion.[[Value]] »).
- Perform !
- Else,
- Perform
AsyncFunctionStart (promiseCapability,ExpressionBody ).
- Perform
- Return
ReturnCompletion (promiseCapability.[[Promise]]).
15.9.4 Runtime Semantics: InstantiateAsyncArrowFunctionExpression
The
- If name is not present, set name to
"" . - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by AsyncArrowFunction . - Let parameters be
AsyncArrowBindingIdentifier . - Let closure be
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText, parameters,AsyncConciseBody ,lexical-this , env, privateEnv). - Perform
SetFunctionName (closure, name). - Return closure.
- If name is not present, set name to
"" . - Let env be the LexicalEnvironment of the
running execution context . - Let privateEnv be the
running execution context 's PrivateEnvironment. - Let sourceText be the
source text matched by AsyncArrowFunction . - Let head be the
AsyncArrowHead that iscovered byCoverCallExpressionAndAsyncArrowHead . - Let parameters be the
ArrowFormalParameters of head. - Let closure be
OrdinaryFunctionCreate (%AsyncFunction.prototype% , sourceText, parameters,AsyncConciseBody ,lexical-this , env, privateEnv). - Perform
SetFunctionName (closure, name). - Return closure.
15.9.5 Runtime Semantics: Evaluation
15.10 Tail Position Calls
15.10.1 Static Semantics: IsInTailPosition ( call )
The abstract operation IsInTailPosition takes argument call (a
- If
IsStrict (call) isfalse , returnfalse . - If call is not contained within a
FunctionBody , aConciseBody , or anAsyncConciseBody , returnfalse . - Let body be the
FunctionBody ,ConciseBody , orAsyncConciseBody that most closely contains call. - If body is the
FunctionBody of aGeneratorBody , returnfalse . - If body is the
FunctionBody of anAsyncFunctionBody , returnfalse . - If body is the
FunctionBody of anAsyncGeneratorBody , returnfalse . - If body is an
AsyncConciseBody , returnfalse . - Return the result of
HasCallInTailPosition of body with argument call.
Tail Position calls are only defined in
15.10.2 Static Semantics: HasCallInTailPosition
The
call is a
A potential tail position call that is immediately followed by return
It is defined piecewise over the following productions:
- Let has be
HasCallInTailPosition ofStatementList with argument call. - If has is
true , returntrue . - Return
HasCallInTailPosition ofStatementListItem with argument call.
- Return
false .
- Let has be
HasCallInTailPosition of the firstStatement with argument call. - If has is
true , returntrue . - Return
HasCallInTailPosition of the secondStatement with argument call.
- Return
HasCallInTailPosition ofStatement with argument call.
- Return
HasCallInTailPosition ofLabelledItem with argument call.
- Return
HasCallInTailPosition ofExpression with argument call.
- Return
HasCallInTailPosition ofCaseBlock with argument call.
- Let has be
false . - If the first
CaseClauses is present, set has toHasCallInTailPosition of the firstCaseClauses with argument call. - If has is
true , returntrue . - Set has to
HasCallInTailPosition ofDefaultClause with argument call. - If has is
true , returntrue . - If the second
CaseClauses is present, set has toHasCallInTailPosition of the secondCaseClauses with argument call. - Return has.
- Let has be
HasCallInTailPosition ofCaseClauses with argument call. - If has is
true , returntrue . - Return
HasCallInTailPosition ofCaseClause with argument call.
- If
StatementList is present, returnHasCallInTailPosition ofStatementList with argument call. - Return
false .
- Return
HasCallInTailPosition ofCatch with argument call.
- Return
HasCallInTailPosition ofFinally with argument call.
- Return
HasCallInTailPosition ofBlock with argument call.
- Return
false .
- Return
HasCallInTailPosition ofAssignmentExpression with argument call.
- Let has be
HasCallInTailPosition of the firstAssignmentExpression with argument call. - If has is
true , returntrue . - Return
HasCallInTailPosition of the secondAssignmentExpression with argument call.
- Return
HasCallInTailPosition ofBitwiseORExpression with argument call.
- Return
HasCallInTailPosition ofLogicalANDExpression with argument call.
- Return
HasCallInTailPosition ofBitwiseORExpression with argument call.
- If this
CallExpression is call, returntrue . - Return
false .
- Return
HasCallInTailPosition ofOptionalChain with argument call.
- Return
false .
- If this
OptionalChain is call, returntrue . - Return
false .
- If this
MemberExpression is call, returntrue . - Return
false .
- Let expr be the
ParenthesizedExpression that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return
HasCallInTailPosition of expr with argument call.
- Return
HasCallInTailPosition ofExpression with argument call.
15.10.3 PrepareForTailCall ( )
The abstract operation PrepareForTailCall takes no arguments and returns
Assert : The currentexecution context will not subsequently be used for the evaluation of any ECMAScript code or built-in functions. The invocation of Call subsequent to the invocation of this abstract operation will create and push a newexecution context before performing any such evaluation.- Discard all resources associated with the current
execution context . - Return
unused .
A tail position call must either release any transient internal resources associated with the currently executing function
For example, a tail position call should only grow an implementation's activation record stack by the amount that the size of the target function's activation record exceeds the size of the calling function's activation record. If the target function's activation record is smaller, then the total size of the stack should decrease.
16 ECMAScript Language: Scripts and Modules
16.1 Scripts
Syntax
16.1.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
LexicallyDeclaredNames ofScriptBody contains any duplicate entries. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofScriptBody also occurs in theVarDeclaredNames ofScriptBody .
-
It is a Syntax Error if
StatementList Contains superunless the source text containingsuperis eval code that is being processed by adirect eval . Additionalearly error rules forsuperwithindirect eval are defined in19.2.1.1 . -
It is a Syntax Error if
StatementList Contains NewTarget unless the source text containingNewTarget is eval code that is being processed by adirect eval . Additionalearly error rules forNewTarget indirect eval are defined in19.2.1.1 . -
It is a Syntax Error if
ContainsDuplicateLabels ofStatementList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedBreakTarget ofStatementList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedContinueTarget ofStatementList with arguments « » and « » istrue . -
It is a Syntax Error if
AllPrivateIdentifiersValid ofStatementList with argument « » isfalse unless the source text containingScriptBody is eval code that is being processed by adirect eval .
16.1.2 Static Semantics: ScriptIsStrict
The
- If
ScriptBody is present and theDirective Prologue ofScriptBody contains aUse Strict Directive , returntrue ; otherwise, returnfalse .
16.1.3 Runtime Semantics: Evaluation
- Return
undefined .
16.1.4 Script Records
A Script Record encapsulates information about a script being evaluated. Each script record contains the fields listed in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Realm]] |
a |
The |
| [[ECMAScriptCode]] |
a |
The result of parsing the source text of this script. |
| [[LoadedModules]] |
a |
A map from the specifier strings imported by this script to the resolved |
| [[HostDefined]] |
anything (default value is |
Field reserved for use by |
16.1.5 ParseScript ( sourceText, realm, hostDefined )
The abstract operation ParseScript takes arguments sourceText (
- Let script be
ParseText (sourceText,Script ). - If script is a
List of errors, return script. - Return
Script Record { [[Realm]]: realm, [[ECMAScriptCode]]: script, [[LoadedModules]]: « », [[HostDefined]]: hostDefined }.
An implementation may parse script source text and analyse it for Early Error conditions prior to evaluation of ParseScript for that script source text. However, the reporting of any errors must be deferred until the point where this specification actually performs ParseScript upon that source text.
16.1.6 ScriptEvaluation ( scriptRecord )
The abstract operation ScriptEvaluation takes argument scriptRecord (a
- Let globalEnv be scriptRecord.[[Realm]].[[GlobalEnv]].
- Let scriptContext be a new
ECMAScript code execution context . - Set the Function of scriptContext to
null . - Set the
Realm of scriptContext to scriptRecord.[[Realm]]. - Set the ScriptOrModule of scriptContext to scriptRecord.
- Set the VariableEnvironment of scriptContext to globalEnv.
- Set the LexicalEnvironment of scriptContext to globalEnv.
- Set the PrivateEnvironment of scriptContext to
null . - Suspend the
running execution context . - Push scriptContext onto the
execution context stack ; scriptContext is now therunning execution context . - Let script be scriptRecord.[[ECMAScriptCode]].
- Let result be
Completion (GlobalDeclarationInstantiation (script, globalEnv)). - If result is a
normal completion , then- Set result to
Completion (Evaluation of script). - If result is a
normal completion and result.[[Value]] isempty , then- Set result to
NormalCompletion (undefined ).
- Set result to
- Set result to
- Suspend scriptContext and remove it from the
execution context stack . Assert : Theexecution context stack is not empty.- Resume the context that is now on the top of the
execution context stack as therunning execution context . - Return ? result.
16.1.7 GlobalDeclarationInstantiation ( script, env )
The abstract operation GlobalDeclarationInstantiation takes arguments script (a
When an
It performs the following steps when called:
- Let lexNames be the
LexicallyDeclaredNames of script. - Let varNames be the
VarDeclaredNames of script. - For each element name of lexNames, do
- If
HasLexicalDeclaration (env, name) istrue , throw aSyntaxError exception. - Let hasRestrictedGlobal be ?
HasRestrictedGlobalProperty (env, name). - NOTE: Global
varandfunctionbindings (except those that are introduced by non-strictdirect eval ) are non-configurable and are therefore restricted global properties. - If hasRestrictedGlobal is
true , throw aSyntaxError exception.
- If
- For each element name of varNames, do
- If
HasLexicalDeclaration (env, name) istrue , throw aSyntaxError exception.
- If
- Let varDeclarations be the
VarScopedDeclarations of script. - Let functionsToInitialize be a new empty
List . - Let declaredFunctionNames be a new empty
List . - For each element d of varDeclarations, in reverse
List order, do- If d is not either a
VariableDeclaration , aForBinding , or aBindingIdentifier , thenAssert : d is either aFunctionDeclaration , aGeneratorDeclaration , anAsyncFunctionDeclaration , or anAsyncGeneratorDeclaration .- NOTE: If there are multiple function declarations for the same name, the last declaration is used.
- Let fn be the sole element of the
BoundNames of d. - If declaredFunctionNames does not contain fn, then
- Let fnDefinable be ?
CanDeclareGlobalFunction (env, fn). - If fnDefinable is
false , throw aTypeError exception. - Append fn to declaredFunctionNames.
- Insert d as the first element of functionsToInitialize.
- Let fnDefinable be ?
- If d is not either a
- Let declaredVarNames be a new empty
List . - For each element d of varDeclarations, do
- If d is either a
VariableDeclaration , aForBinding , or aBindingIdentifier , then- For each String vn of the
BoundNames of d, do- If declaredFunctionNames does not contain vn, then
- Let vnDefinable be ?
CanDeclareGlobalVar (env, vn). - If vnDefinable is
false , throw aTypeError exception. - If declaredVarNames does not contain vn, then
- Append vn to declaredVarNames.
- Let vnDefinable be ?
- If declaredFunctionNames does not contain vn, then
- For each String vn of the
- If d is either a
- NOTE: No abnormal terminations occur after this algorithm step if the
global object is anordinary object . However, if theglobal object is aProxy exotic object it may exhibit behaviours that cause abnormal terminations in some of the following steps. - NOTE: Annex
B.3.2.2 adds additional steps at this point. - Let lexDeclarations be the
LexicallyScopedDeclarations of script. - Let privateEnv be
null . - For each element d of lexDeclarations, do
- NOTE: Lexically declared names are only instantiated here but not initialized.
- For each element dn of the
BoundNames of d, do- If
IsConstantDeclaration of d istrue , then- Perform ? env.CreateImmutableBinding(dn,
true ).
- Perform ? env.CreateImmutableBinding(dn,
- Else,
- Perform ? env.CreateMutableBinding(dn,
false ).
- Perform ? env.CreateMutableBinding(dn,
- If
- For each
Parse Node f of functionsToInitialize, do- Let fn be the sole element of the
BoundNames of f. - Let fo be
InstantiateFunctionObject of f with arguments env and privateEnv. - Perform ?
CreateGlobalFunctionBinding (env, fn, fo,false ).
- Let fn be the sole element of the
- For each String vn of declaredVarNames, do
- Perform ?
CreateGlobalVarBinding (env, vn,false ).
- Perform ?
- Return
unused .
Unlike explicit var or function declarations, properties that are directly created on the
16.2 Modules
Syntax
16.2.1 Module Semantics
16.2.1.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
LexicallyDeclaredNames ofModuleItemList contains any duplicate entries. -
It is a Syntax Error if any element of the
LexicallyDeclaredNames ofModuleItemList also occurs in theVarDeclaredNames ofModuleItemList . -
It is a Syntax Error if the
ExportedNames ofModuleItemList contains any duplicate entries. -
It is a Syntax Error if any element of the
ExportedBindings ofModuleItemList does not also occur in either theVarDeclaredNames ofModuleItemList , or theLexicallyDeclaredNames ofModuleItemList . -
It is a Syntax Error if
ModuleItemList Contains super. -
It is a Syntax Error if
ModuleItemList Contains NewTarget . -
It is a Syntax Error if
ContainsDuplicateLabels ofModuleItemList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedBreakTarget ofModuleItemList with argument « » istrue . -
It is a Syntax Error if
ContainsUndefinedContinueTarget ofModuleItemList with arguments « » and « » istrue . -
It is a Syntax Error if
AllPrivateIdentifiersValid ofModuleItemList with argument « » isfalse .
The duplicate export default
- It is a Syntax Error if
IsStringWellFormedUnicode (SV ofStringLiteral ) isfalse .
16.2.1.2 Static Semantics: ImportedLocalNames ( importEntries )
The abstract operation ImportedLocalNames takes argument importEntries (a
- Let localNames be a new empty
List . - For each
ImportEntry Record i of importEntries, do- Append i.[[LocalName]] to localNames.
- Return localNames.
16.2.1.3 ModuleRequest Records
A ModuleRequest Record represents the request to import a module with given import attributes. It consists of the following fields:
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Specifier]] | a String | The module specifier |
| [[Attributes]] |
a |
The import attributes |
A LoadedModuleRequest Record represents the request to import a module together with the resulting
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Specifier]] | a String | The module specifier |
| [[Attributes]] |
a |
The import attributes |
| [[Module]] |
a |
The loaded module corresponding to this module request |
An ImportAttribute Record consists of the following fields:
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Key]] | a String | The attribute key |
| [[Value]] | a String | The attribute value |
16.2.1.3.1 ModuleRequestsEqual ( left, right )
The abstract operation ModuleRequestsEqual takes arguments left (a
- If left.[[Specifier]] is not right.[[Specifier]], return
false . - Let leftAttrs be left.[[Attributes]].
- Let rightAttrs be right.[[Attributes]].
- Let leftAttrsCount be the number of elements in leftAttrs.
- Let rightAttrsCount be the number of elements in rightAttrs.
- If leftAttrsCount ≠ rightAttrsCount, return
false . - For each
ImportAttribute Record l of leftAttrs, do- If rightAttrs does not contain an
ImportAttribute Record r such that l.[[Key]] is r.[[Key]] and l.[[Value]] is r.[[Value]], returnfalse .
- If rightAttrs does not contain an
- Return
true .
16.2.1.4 Static Semantics: ModuleRequests
The
- Return a new empty
List .
- Return the
ModuleRequests ofModuleItem .
- Let requests be the
ModuleRequests ofModuleItemList . - Let additionalRequests be the
ModuleRequests ofModuleItem . - For each
ModuleRequest Record mr of additionalRequests, do- If requests does not contain a
ModuleRequest Record mr2 such thatModuleRequestsEqual (mr, mr2) istrue , then- Append mr to requests.
- If requests does not contain a
- Return requests.
- Return a new empty
List .
- Let specifier be the
SV ofFromClause . - Return a
List whose sole element is theModuleRequest Record { [[Specifier]]: specifier, [[Attributes]]: « » }.
- Let specifier be the
SV ofFromClause . - Let attributes be
WithClauseToAttributes ofWithClause . - Return a
List whose sole element is theModuleRequest Record { [[Specifier]]: specifier, [[Attributes]]: attributes }.
- Let specifier be the
SV ofModuleSpecifier . - Return a
List whose sole element is theModuleRequest Record { [[Specifier]]: specifier, [[Attributes]]: « » }.
- Let specifier be the
SV ofModuleSpecifier . - Let attributes be
WithClauseToAttributes ofWithClause . - Return a
List whose sole element is theModuleRequest Record { [[Specifier]]: specifier, [[Attributes]]: attributes }.
- Let specifier be the
SV ofFromClause . - Return a
List whose sole element is theModuleRequest Record { [[Specifier]]: specifier, [[Attributes]]: « » }.
- Let specifier be the
SV ofFromClause . - Let attributes be
WithClauseToAttributes ofWithClause . - Return a
List whose sole element is theModuleRequest Record { [[Specifier]]: specifier, [[Attributes]]: attributes }.
- Return a new empty
List .
16.2.1.5 Abstract Module Records
A Module Record encapsulates structural information about the imports and exports of a single module. This information is used to link the imports and exports of sets of connected modules. A Module Record includes four fields that are only used when evaluating a module.
For specification purposes Module Record values are values of the
Module Record defines the fields listed in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Realm]] |
a |
The |
| [[Environment]] |
a |
The |
| [[Namespace]] |
an Object or |
The Module Namespace Object ( |
| [[HostDefined]] |
anything (default value is |
Field reserved for use by |
| Method | Purpose |
|---|---|
| LoadRequestedModules([hostDefined]) |
Prepares the module for linking by recursively loading all its dependencies, and returns a promise. |
| GetExportedNames([exportStarSet]) |
Return a list of all names that are either directly or indirectly exported from this module. LoadRequestedModules must have completed successfully prior to invoking this method. |
| ResolveExport(exportName [, resolveSet]) |
Return the binding of a name exported by this module. Bindings are represented by a ResolvedBinding Record, of the form { [[Module]]: Each time this operation is called with a specific exportName, resolveSet pair as arguments it must return the same result. LoadRequestedModules must have completed successfully prior to invoking this method. |
| Link() |
Prepare the module for evaluation by transitively resolving all module dependencies and creating a LoadRequestedModules must have completed successfully prior to invoking this method. |
| Evaluate() |
Returns a promise for the evaluation of this module and its dependencies, resolving on successful evaluation or if it has already been evaluated successfully, and rejecting for an evaluation error or if it has already been evaluated unsuccessfully. If the promise is rejected, Link must have completed successfully prior to invoking this method. |
16.2.1.6 Cyclic Module Records
A Cyclic Module Record is used to represent information about a module that can participate in dependency cycles with other modules that are subclasses of the
In addition to the fields defined in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Status]] |
|
Initially |
| [[EvaluationError]] |
a |
A |
| [[DFSIndex]] |
an |
Auxiliary field used during Link and Evaluate only. If [[Status]] is either |
| [[DFSAncestorIndex]] |
an |
Auxiliary field used during Link and Evaluate only. If [[Status]] is either |
| [[RequestedModules]] |
a |
A |
| [[LoadedModules]] |
a |
A map from the specifier strings used by the module represented by this record to request the importation of a module with the relative import attributes to the resolved |
| [[CycleRoot]] |
a |
The first visited module of the cycle, the root DFS ancestor of the strongly connected component. For a module not in a cycle, this would be the module itself. Once Evaluate has completed, a module's [[DFSAncestorIndex]] is the [[DFSIndex]] of its [[CycleRoot]]. |
| [[HasTLA]] | a Boolean |
Whether this module is individually asynchronous (for example, if it's a |
| [[AsyncEvaluationOrder]] |
|
This field is initially set to |
| [[TopLevelCapability]] |
a |
If this module is the [[CycleRoot]] of some cycle, and Evaluate() was called on some module in that cycle, this field contains the |
| [[AsyncParentModules]] |
a |
If this module or a dependency has [[HasTLA]] |
| [[PendingAsyncDependencies]] |
an |
If this module has any asynchronous dependencies, this tracks the number of asynchronous dependency modules remaining to execute for this module. A module with asynchronous dependencies will be executed when this field reaches 0 and there are no execution errors. |
In addition to the methods defined in
| Method | Purpose |
|---|---|
| InitializeEnvironment() |
Initialize the |
| ExecuteModule([promiseCapability]) |
Evaluate the module's code within its |
A GraphLoadingState Record is a
| Field Name | Value Type | Meaning |
|---|---|---|
| [[PromiseCapability]] |
a |
The promise to resolve when the loading process finishes. |
| [[IsLoading]] | a Boolean | It is true if the loading process has not finished yet, neither successfully nor with an error. |
| [[PendingModulesCount]] |
a non-negative |
It tracks the number of pending |
| [[Visited]] |
a |
It is a list of the |
| [[HostDefined]] |
anything (default value is |
It contains |
16.2.1.6.1 LoadRequestedModules ( [ hostDefined ] )
The LoadRequestedModules concrete method of a
- If hostDefined is not present, let hostDefined be
empty . - Let pc be !
NewPromiseCapability (%Promise% ). - Let state be the
GraphLoadingState Record { [[IsLoading]]:true , [[PendingModulesCount]]: 1, [[Visited]]: « », [[PromiseCapability]]: pc, [[HostDefined]]: hostDefined }. - Perform
InnerModuleLoading (state, module). - Return pc.[[Promise]].
<link rel="preload" as="..."> tags.
import() expressions never set the hostDefined parameter.
16.2.1.6.1.1 InnerModuleLoading ( state, module )
The abstract operation InnerModuleLoading takes arguments state (a
Assert : state.[[IsLoading]] istrue .- If module is a
Cyclic Module Record , module.[[Status]] isnew , and state.[[Visited]] does not contain module, then- Append module to state.[[Visited]].
- Let requestedModulesCount be the number of elements in module.[[RequestedModules]].
- Set state.[[PendingModulesCount]] to state.[[PendingModulesCount]] + requestedModulesCount.
- For each
ModuleRequest Record request of module.[[RequestedModules]], do- If
AllImportAttributesSupported (request.[[Attributes]]) isfalse , then- Let error be
ThrowCompletion (a newly createdSyntaxError object). - Perform
ContinueModuleLoading (state, error).
- Let error be
- Else if module.[[LoadedModules]] contains a
LoadedModuleRequest Record record such thatModuleRequestsEqual (record, request) istrue , then- Perform
InnerModuleLoading (state, record.[[Module]]).
- Perform
- Else,
- Perform
HostLoadImportedModule (module, request, state.[[HostDefined]], state). - NOTE:
HostLoadImportedModule will callFinishLoadingImportedModule , which re-enters the graph loading process throughContinueModuleLoading .
- Perform
- If state.[[IsLoading]] is
false , returnunused .
- If
Assert : state.[[PendingModulesCount]] ≥ 1.- Set state.[[PendingModulesCount]] to state.[[PendingModulesCount]] - 1.
- If state.[[PendingModulesCount]] = 0, then
- Set state.[[IsLoading]] to
false . - For each
Cyclic Module Record loaded of state.[[Visited]], do- If loaded.[[Status]] is
new , set loaded.[[Status]] tounlinked .
- If loaded.[[Status]] is
- Perform !
Call (state.[[PromiseCapability]].[[Resolve]],undefined , «undefined »).
- Set state.[[IsLoading]] to
- Return
unused .
16.2.1.6.1.2 ContinueModuleLoading ( state, moduleCompletion )
The abstract operation ContinueModuleLoading takes arguments state (a
- If state.[[IsLoading]] is
false , returnunused . - If moduleCompletion is a
normal completion , then- Perform
InnerModuleLoading (state, moduleCompletion.[[Value]]).
- Perform
- Else,
- Set state.[[IsLoading]] to
false . - Perform !
Call (state.[[PromiseCapability]].[[Reject]],undefined , « moduleCompletion.[[Value]] »).
- Set state.[[IsLoading]] to
- Return
unused .
16.2.1.6.2 Link ( )
The Link concrete method of a
Assert : module.[[Status]] is one ofunlinked ,linked ,evaluating-async , orevaluated .- Let stack be a new empty
List . - Let result be
Completion (InnerModuleLinking (module, stack, 0)). - If result is an
abrupt completion , then- For each
Cyclic Module Record m of stack, doAssert : m.[[Status]] islinking .- Set m.[[Status]] to
unlinked .
Assert : module.[[Status]] isunlinked .- Return ? result.
- For each
Assert : module.[[Status]] is one oflinked ,evaluating-async , orevaluated .Assert : stack is empty.- Return
unused .
16.2.1.6.2.1 InnerModuleLinking ( module, stack, index )
The abstract operation InnerModuleLinking takes arguments module (a
- If module is not a
Cyclic Module Record , then- Perform ? module.Link().
- Return index.
- If module.[[Status]] is one of
linking ,linked ,evaluating-async , orevaluated , then- Return index.
Assert : module.[[Status]] isunlinked .- Set module.[[Status]] to
linking . - Set module.[[DFSIndex]] to index.
- Set module.[[DFSAncestorIndex]] to index.
- Set index to index + 1.
- Append module to stack.
- For each
ModuleRequest Record request of module.[[RequestedModules]], do- Let requiredModule be
GetImportedModule (module, request). - Set index to ?
InnerModuleLinking (requiredModule, stack, index). - If requiredModule is a
Cyclic Module Record , thenAssert : requiredModule.[[Status]] is one oflinking ,linked ,evaluating-async , orevaluated .Assert : requiredModule.[[Status]] islinking if and only if stack contains requiredModule.- If requiredModule.[[Status]] is
linking , then- Set module.[[DFSAncestorIndex]] to
min (module.[[DFSAncestorIndex]], requiredModule.[[DFSAncestorIndex]]).
- Set module.[[DFSAncestorIndex]] to
- Let requiredModule be
- Perform ? module.InitializeEnvironment().
Assert : module occurs exactly once in stack.Assert : module.[[DFSAncestorIndex]] ≤ module.[[DFSIndex]].- If module.[[DFSAncestorIndex]] = module.[[DFSIndex]], then
- Let done be
false . - Repeat, while done is
false ,- Let requiredModule be the last element of stack.
- Remove the last element of stack.
Assert : requiredModule is aCyclic Module Record .- Set requiredModule.[[Status]] to
linked . - If requiredModule and module are the same
Module Record , set done totrue .
- Let done be
- Return index.
16.2.1.6.3 Evaluate ( )
The Evaluate concrete method of a
Assert : This call to Evaluate is not happening at the same time as another call to Evaluate within thesurrounding agent .Assert : module.[[Status]] is one oflinked ,evaluating-async , orevaluated .- If module.[[Status]] is either
evaluating-async orevaluated , set module to module.[[CycleRoot]]. - If module.[[TopLevelCapability]] is not
empty , then- Return module.[[TopLevelCapability]].[[Promise]].
- Let stack be a new empty
List . - Let capability be !
NewPromiseCapability (%Promise% ). - Set module.[[TopLevelCapability]] to capability.
- Let result be
Completion (InnerModuleEvaluation (module, stack, 0)). - If result is an
abrupt completion , then- For each
Cyclic Module Record m of stack, do Assert : module.[[Status]] isevaluated .Assert : module.[[EvaluationError]] and result are the sameCompletion Record .- Perform !
Call (capability.[[Reject]],undefined , « result.[[Value]] »).
- For each
- Else,
- Return capability.[[Promise]].
16.2.1.6.3.1 InnerModuleEvaluation ( module, stack, index )
The abstract operation InnerModuleEvaluation takes arguments module (a
- If module is not a
Cyclic Module Record , then- Let promise be ! module.Evaluate().
Assert : promise.[[PromiseState]] is notpending .- If promise.[[PromiseState]] is
rejected , then- Return
ThrowCompletion (promise.[[PromiseResult]]).
- Return
- Return index.
- If module.[[Status]] is either
evaluating-async orevaluated , then- If module.[[EvaluationError]] is
empty , return index. - Otherwise, return ? module.[[EvaluationError]].
- If module.[[EvaluationError]] is
- If module.[[Status]] is
evaluating , return index. Assert : module.[[Status]] islinked .- Set module.[[Status]] to
evaluating . - Set module.[[DFSIndex]] to index.
- Set module.[[DFSAncestorIndex]] to index.
- Set module.[[PendingAsyncDependencies]] to 0.
- Set index to index + 1.
- Append module to stack.
- For each
ModuleRequest Record request of module.[[RequestedModules]], do- Let requiredModule be
GetImportedModule (module, request). - Set index to ?
InnerModuleEvaluation (requiredModule, stack, index). - If requiredModule is a
Cyclic Module Record , thenAssert : requiredModule.[[Status]] is one ofevaluating ,evaluating-async , orevaluated .Assert : requiredModule.[[Status]] isevaluating if and only if stack contains requiredModule.- If requiredModule.[[Status]] is
evaluating , then- Set module.[[DFSAncestorIndex]] to
min (module.[[DFSAncestorIndex]], requiredModule.[[DFSAncestorIndex]]).
- Set module.[[DFSAncestorIndex]] to
- Else,
- Set requiredModule to requiredModule.[[CycleRoot]].
Assert : requiredModule.[[Status]] is eitherevaluating-async orevaluated .- If requiredModule.[[EvaluationError]] is not
empty , return ? requiredModule.[[EvaluationError]].
- If requiredModule.[[AsyncEvaluationOrder]] is an
integer , then- Set module.[[PendingAsyncDependencies]] to module.[[PendingAsyncDependencies]] + 1.
- Append module to requiredModule.[[AsyncParentModules]].
- Let requiredModule be
- If module.[[PendingAsyncDependencies]] > 0 or module.[[HasTLA]] is
true , thenAssert : module.[[AsyncEvaluationOrder]] isunset .- Set module.[[AsyncEvaluationOrder]] to
IncrementModuleAsyncEvaluationCount (). - If module.[[PendingAsyncDependencies]] = 0, perform
ExecuteAsyncModule (module).
- Else,
- Perform ? module.ExecuteModule().
Assert : module occurs exactly once in stack.Assert : module.[[DFSAncestorIndex]] ≤ module.[[DFSIndex]].- If module.[[DFSAncestorIndex]] = module.[[DFSIndex]], then
- Let done be
false . - Repeat, while done is
false ,- Let requiredModule be the last element of stack.
- Remove the last element of stack.
Assert : requiredModule is aCyclic Module Record .Assert : requiredModule.[[AsyncEvaluationOrder]] is either aninteger orunset .- If requiredModule.[[AsyncEvaluationOrder]] is
unset , set requiredModule.[[Status]] toevaluated . - Otherwise, set requiredModule.[[Status]] to
evaluating-async . - If requiredModule and module are the same
Module Record , set done totrue . - Set requiredModule.[[CycleRoot]] to module.
- Let done be
- Return index.
A module is
Any modules depending on a module of an asynchronous cycle when that cycle is not
16.2.1.6.3.2 ExecuteAsyncModule ( module )
The abstract operation ExecuteAsyncModule takes argument module (a
Assert : module.[[Status]] is eitherevaluating orevaluating-async .Assert : module.[[HasTLA]] istrue .- Let capability be !
NewPromiseCapability (%Promise% ). - Let fulfilledClosure be a new
Abstract Closure with no parameters that captures module and performs the following steps when called:- Perform
AsyncModuleExecutionFulfilled (module). - Return
undefined .
- Perform
- Let onFulfilled be
CreateBuiltinFunction (fulfilledClosure, 0,"" , « »). - Let rejectedClosure be a new
Abstract Closure with parameters (error) that captures module and performs the following steps when called:- Perform
AsyncModuleExecutionRejected (module, error). - Return
undefined .
- Perform
- Let onRejected be
CreateBuiltinFunction (rejectedClosure, 0,"" , « »). - Perform
PerformPromiseThen (capability.[[Promise]], onFulfilled, onRejected). - Perform ! module.ExecuteModule(capability).
- Return
unused .
16.2.1.6.3.3 GatherAvailableAncestors ( module, execList )
The abstract operation GatherAvailableAncestors takes arguments module (a
- For each
Cyclic Module Record m of module.[[AsyncParentModules]], do- If execList does not contain m and m.[[CycleRoot]].[[EvaluationError]] is
empty , thenAssert : m.[[Status]] isevaluating-async .Assert : m.[[EvaluationError]] isempty .Assert : m.[[AsyncEvaluationOrder]] is aninteger .Assert : m.[[PendingAsyncDependencies]] > 0.- Set m.[[PendingAsyncDependencies]] to m.[[PendingAsyncDependencies]] - 1.
- If m.[[PendingAsyncDependencies]] = 0, then
- Append m to execList.
- If m.[[HasTLA]] is
false , performGatherAvailableAncestors (m, execList).
- If execList does not contain m and m.[[CycleRoot]].[[EvaluationError]] is
- Return
unused .
When an asynchronous execution for a root module is fulfilled, this function determines the list of modules which are able to synchronously execute together on this completion, populating them in execList.
16.2.1.6.3.4 AsyncModuleExecutionFulfilled ( module )
The abstract operation AsyncModuleExecutionFulfilled takes argument module (a
- If module.[[Status]] is
evaluated , thenAssert : module.[[EvaluationError]] is notempty .- Return
unused .
Assert : module.[[Status]] isevaluating-async .Assert : module.[[AsyncEvaluationOrder]] is aninteger .Assert : module.[[EvaluationError]] isempty .- Set module.[[AsyncEvaluationOrder]] to
done . - Set module.[[Status]] to
evaluated . - If module.[[TopLevelCapability]] is not
empty , thenAssert : module.[[CycleRoot]] and module are the sameModule Record .- Perform !
Call (module.[[TopLevelCapability]].[[Resolve]],undefined , «undefined »).
- Let execList be a new empty
List . - Perform
GatherAvailableAncestors (module, execList). Assert : All elements of execList have their [[AsyncEvaluationOrder]] field set to aninteger , [[PendingAsyncDependencies]] field set to 0, and [[EvaluationError]] field set toempty .- Let sortedExecList be a
List whose elements are the elements of execList, sorted by their [[AsyncEvaluationOrder]] field in ascending order. - For each
Cyclic Module Record m of sortedExecList, do- If m.[[Status]] is
evaluated , thenAssert : m.[[EvaluationError]] is notempty .
- Else if m.[[HasTLA]] is
true , then- Perform
ExecuteAsyncModule (m).
- Perform
- Else,
- Let result be m.ExecuteModule().
- If result is an
abrupt completion , then- Perform
AsyncModuleExecutionRejected (m, result.[[Value]]).
- Perform
- Else,
- Set m.[[AsyncEvaluationOrder]] to
done . - Set m.[[Status]] to
evaluated . - If m.[[TopLevelCapability]] is not
empty , thenAssert : m.[[CycleRoot]] and m are the sameModule Record .- Perform !
Call (m.[[TopLevelCapability]].[[Resolve]],undefined , «undefined »).
- Set m.[[AsyncEvaluationOrder]] to
- If m.[[Status]] is
- Return
unused .
16.2.1.6.3.5 AsyncModuleExecutionRejected ( module, error )
The abstract operation AsyncModuleExecutionRejected takes arguments module (a
- If module.[[Status]] is
evaluated , thenAssert : module.[[EvaluationError]] is notempty .- Return
unused .
Assert : module.[[Status]] isevaluating-async .Assert : module.[[AsyncEvaluationOrder]] is aninteger .Assert : module.[[EvaluationError]] isempty .- Set module.[[EvaluationError]] to
ThrowCompletion (error). - Set module.[[Status]] to
evaluated . - Set module.[[AsyncEvaluationOrder]] to
done . - NOTE: module.[[AsyncEvaluationOrder]] is set to
done for symmetry withAsyncModuleExecutionFulfilled . InInnerModuleEvaluation , the value of a module's [[AsyncEvaluationOrder]] internal slot is unused when its [[EvaluationError]] internal slot is notempty . - For each
Cyclic Module Record m of module.[[AsyncParentModules]], do- Perform
AsyncModuleExecutionRejected (m, error).
- Perform
- If module.[[TopLevelCapability]] is not
empty , thenAssert : module.[[CycleRoot]] and module are the sameModule Record .- Perform !
Call (module.[[TopLevelCapability]].[[Reject]],undefined , « error »).
- Return
unused .
16.2.1.6.4 Example Cyclic Module Record Graphs
This non-normative section gives a series of examples of the linking and evaluation of a few common module graphs, with a specific focus on how errors can occur.
First consider the following simple module graph:
Let's first assume that there are no error conditions. When a
Consider then cases involving linking errors, after a successful call to A.LoadRequestedModules(). If
Finally, consider a case involving evaluation errors after a successful call to Link(). If
Now consider a different type of error condition:
In this scenario, module A declares a dependency on some other module, but no
The difference here between loading, linking and evaluation errors is due to the following characteristic:
Evaluation must be only performed once, as it can cause side effects; it is thus important to remember whether evaluation has already been performed, even if unsuccessfully. (In the error case, it makes sense to also remember the exception because otherwise subsequent Evaluate() calls would have to synthesize a new one.)- Linking, on the other hand, is side-effect-free, and thus even if it fails, it can be retried at a later time with no issues.
- Loading closely interacts with the
host , and it may be desirable for some of them to allow users to retry failed loads (for example, if the failure is caused by temporarily bad network conditions).
Now, consider a module graph with a cycle:
Here we assume that the entry point is module A, so that the
Then the
An analogous story occurs for the evaluation phase of a cyclic module graph, in the success case.
Now consider a case where A has a linking error; for example, it tries to import a binding from C that does not exist. In that case, the above steps still occur, including the early return from the second call to
Alternatively, consider a case where A has an evaluation error; for example, its source code throws an exception. In that case, the evaluation-time analogue of the above steps still occurs, including the early return from the second call to await through the whole dependency graph through the
Lastly, consider a module graph with a cycle, where all modules complete asynchronously:
Loading and linking happen as before, and all modules end up with [[Status]] set to
Calling A.Evaluate() calls
|
Field
|
A | B | C | D | E |
|---|---|---|---|---|---|
| [[DFSIndex]] | 0 | 1 | 3 | 2 | 4 |
| [[DFSAncestorIndex]] | 0 | 0 | 0 | 0 | 4 |
| [[Status]] | |||||
| [[AsyncEvaluationOrder]] | 4 | 1 | 3 | 0 | 2* |
| [[AsyncParentModules]] | « » | « A » | « A » | « B, C » | « C » |
| [[PendingAsyncDependencies]] | 2 (B and C) | 1 (D) | 2 (D and E) | 0 | 0 |
Let us assume that E finishes executing first. When that happens,
| Fields / Modules | C | E |
|---|---|---|
| [[DFSIndex]] | 3 | 4 |
| [[DFSAncestorIndex]] | 0 | 4 |
| [[Status]] | ||
| [[AsyncEvaluationOrder]] | 3 | 2 |
| [[AsyncParentModules]] | « A » | « C » |
| [[PendingAsyncDependencies]] | 1 (D) | 0 |
D is next to finish (as it was the only module that was still executing). When that happens, await). The fields of the updated modules are as given in
| Fields / Module | B | C | D |
|---|---|---|---|
| [[DFSIndex]] | 1 | 3 | 2 |
| [[DFSAncestorIndex]] | 0 | 0 | 0 |
| [[Status]] | |||
| [[AsyncEvaluationOrder]] | 1 | 3 | 0 |
| [[AsyncParentModules]] | « A » | « A » | « B, C » |
| [[PendingAsyncDependencies]] | 0 | 0 | 0 |
Let us assume that C finishes executing next. When that happens,
| Fields / Modules | A | C |
|---|---|---|
| [[DFSIndex]] | 0 | 3 |
| [[DFSAncestorIndex]] | 0 | 0 |
| [[Status]] | ||
| [[AsyncEvaluationOrder]] | 4 | 3 |
| [[AsyncParentModules]] | « » | « A » |
| [[PendingAsyncDependencies]] | 1 (B) | 0 |
Then, B finishes executing. When that happens,
| Fields / Modules | A | B |
|---|---|---|
| [[DFSIndex]] | 0 | 1 |
| [[DFSAncestorIndex]] | 0 | 0 |
| [[Status]] | ||
| [[AsyncEvaluationOrder]] | 4 | 1 |
| [[AsyncParentModules]] | « » | « A » |
| [[PendingAsyncDependencies]] | 0 | 0 |
Finally, A finishes executing. When that happens,
| Fields / Modules | A |
|---|---|
| [[DFSIndex]] | 0 |
| [[DFSAncestorIndex]] | 0 |
| [[Status]] | |
| [[AsyncEvaluationOrder]] | 4 |
| [[AsyncParentModules]] | « » |
| [[PendingAsyncDependencies]] | 0 |
Alternatively, consider a failure case where C fails execution and returns an error before B has finished executing. When that happens,
| Fields / Modules | A | C |
|---|---|---|
| [[DFSIndex]] | 0 | 3 |
| [[DFSAncestorIndex]] | 0 | 0 |
| [[Status]] | ||
| [[AsyncEvaluationOrder]] | 4 | 3 |
| [[AsyncParentModules]] | « » | « A » |
| [[PendingAsyncDependencies]] | 1 (B) | 0 |
| [[EvaluationError]] | C's evaluation error |
A will be rejected with the same error as C since C will call
| Fields / Modules | A |
|---|---|
| [[DFSIndex]] | 0 |
| [[DFSAncestorIndex]] | 0 |
| [[Status]] | |
| [[AsyncEvaluationOrder]] | 4 |
| [[AsyncParentModules]] | « » |
| [[PendingAsyncDependencies]] | 0 |
| [[EvaluationError]] | C's |
Then, B finishes executing without an error. When that happens,
| Fields / Modules | A | B |
|---|---|---|
| [[DFSIndex]] | 0 | 1 |
| [[DFSAncestorIndex]] | 0 | 0 |
| [[Status]] | ||
| [[AsyncEvaluationOrder]] | 4 | 1 |
| [[AsyncParentModules]] | « » | « A » |
| [[PendingAsyncDependencies]] | 0 | 0 |
| [[EvaluationError]] | C's |
16.2.1.7 Source Text Module Records
A Source Text Module Record is used to represent information about a module that was defined from
A
In addition to the fields defined in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[ECMAScriptCode]] |
a |
The result of parsing the source text of this module using |
| [[Context]] |
an |
The |
| [[ImportMeta]] |
an Object or |
An object exposed through the import.meta meta property. It is |
| [[ImportEntries]] |
a |
A |
| [[LocalExportEntries]] |
a |
A |
| [[IndirectExportEntries]] |
a |
A export * as namespace declarations.
|
| [[StarExportEntries]] |
a |
A export * declarations that occur within the module, not including export * as namespace declarations.
|
An ImportEntry Record is a
| Field Name | Value Type | Meaning |
|---|---|---|
| [[ModuleRequest]] |
a |
|
| [[ImportName]] |
a String or |
The name under which the desired binding is exported by the module identified by [[ModuleRequest]]. The value |
| [[LocalName]] | a String | The name that is used to locally access the imported value from within the importing module. |
| Import Statement Form | [[ModuleRequest]] | [[ImportName]] | [[LocalName]] |
|---|---|---|---|
import v from "mod";
|
|
|
|
import * as ns from "mod";
|
|
|
|
import {x} from "mod";
|
|
|
|
import {x as v} from "mod";
|
|
|
|
import "mod";
|
An |
||
An ExportEntry Record is a
| Field Name | Value Type | Meaning |
|---|---|---|
| [[ExportName]] |
a String or |
The name used to export this binding by this module. |
| [[ModuleRequest]] |
a |
The |
| [[ImportName]] |
a String, |
The name under which the desired binding is exported by the module identified by [[ModuleRequest]]. export * as ns from "mod" declarations. export * from "mod" declarations.
|
| [[LocalName]] |
a String or |
The name that is used to locally access the exported value from within the importing module. |
| Export Statement Form | [[ExportName]] | [[ModuleRequest]] | [[ImportName]] | [[LocalName]] |
|---|---|---|---|---|
export var v;
|
|
|
|
|
export default function f() {}
|
|
|
|
|
export default function () {}
|
|
|
|
|
export default 42;
|
|
|
|
|
export {x};
|
|
|
|
|
export {v as x};
|
|
|
|
|
export {x} from "mod";
|
|
|
|
|
export {v as x} from "mod";
|
|
|
|
|
export * from "mod";
|
|
|
|
|
export * as ns from "mod";
|
|
|
|
|
The following definitions specify the required concrete methods and other
16.2.1.7.1 ParseModule ( sourceText, realm, hostDefined )
The abstract operation ParseModule takes arguments sourceText (
- Let body be
ParseText (sourceText,Module ). - If body is a
List of errors, return body. - Let requestedModules be the
ModuleRequests of body. - Let importEntries be the
ImportEntries of body. - Let importedBoundNames be
ImportedLocalNames (importEntries). - Let indirectExportEntries be a new empty
List . - Let localExportEntries be a new empty
List . - Let starExportEntries be a new empty
List . - Let exportEntries be the
ExportEntries of body. - For each
ExportEntry Record ee of exportEntries, do- If ee.[[ModuleRequest]] is
null , then- If importedBoundNames does not contain ee.[[LocalName]], then
- Append ee to localExportEntries.
- Else,
- Let ie be the element of importEntries whose [[LocalName]] is ee.[[LocalName]].
- If ie.[[ImportName]] is
namespace-object , then- NOTE: This is a re-export of an imported module namespace object.
- Append ee to localExportEntries.
- Else,
- NOTE: This is a re-export of a single name.
- Append the
ExportEntry Record { [[ModuleRequest]]: ie.[[ModuleRequest]], [[ImportName]]: ie.[[ImportName]], [[LocalName]]:null , [[ExportName]]: ee.[[ExportName]] } to indirectExportEntries.
- If importedBoundNames does not contain ee.[[LocalName]], then
- Else if ee.[[ImportName]] is
all-but-default , thenAssert : ee.[[ExportName]] isnull .- Append ee to starExportEntries.
- Else,
- Append ee to indirectExportEntries.
- If ee.[[ModuleRequest]] is
- Let async be body
Contains await. - Return
Source Text Module Record { [[Realm]]: realm, [[Environment]]:empty , [[Namespace]]:empty , [[CycleRoot]]:empty , [[HasTLA]]: async, [[AsyncEvaluationOrder]]:unset , [[TopLevelCapability]]:empty , [[AsyncParentModules]]: « », [[PendingAsyncDependencies]]:empty , [[Status]]:new , [[EvaluationError]]:empty , [[HostDefined]]: hostDefined, [[ECMAScriptCode]]: body, [[Context]]:empty , [[ImportMeta]]:empty , [[RequestedModules]]: requestedModules, [[LoadedModules]]: « », [[ImportEntries]]: importEntries, [[LocalExportEntries]]: localExportEntries, [[IndirectExportEntries]]: indirectExportEntries, [[StarExportEntries]]: starExportEntries, [[DFSIndex]]:empty , [[DFSAncestorIndex]]:empty }.
An implementation may parse module source text and analyse it for Early Error conditions prior to the evaluation of ParseModule for that module source text. However, the reporting of any errors must be deferred until the point where this specification actually performs ParseModule upon that source text.
16.2.1.7.2 GetExportedNames ( [ exportStarSet ] )
The GetExportedNames concrete method of a
Assert : module.[[Status]] is notnew .- If exportStarSet is not present, set exportStarSet to a new empty
List . - If exportStarSet contains module, then
- Append module to exportStarSet.
- Let exportedNames be a new empty
List . - For each
ExportEntry Record e of module.[[LocalExportEntries]], do - For each
ExportEntry Record e of module.[[IndirectExportEntries]], do - For each
ExportEntry Record e of module.[[StarExportEntries]], doAssert : e.[[ModuleRequest]] is notnull .- Let requestedModule be
GetImportedModule (module, e.[[ModuleRequest]]). - Let starNames be requestedModule.GetExportedNames(exportStarSet).
- For each element n of starNames, do
- If n is not
"default" , then- If exportedNames does not contain n, then
- Append n to exportedNames.
- If exportedNames does not contain n, then
- If n is not
- Return exportedNames.
GetExportedNames does not filter out or throw an exception for names that have ambiguous star export bindings.
16.2.1.7.3 ResolveExport ( exportName [ , resolveSet ] )
The ResolveExport concrete method of a
ResolveExport attempts to resolve an imported binding to the actual defining module and local binding name. The defining module may be the module represented by the
If a defining module is found, a
It performs the following steps when called:
Assert : module.[[Status]] is notnew .- If resolveSet is not present, set resolveSet to a new empty
List . - For each
Record { [[Module]], [[ExportName]] } r of resolveSet, do- If module and r.[[Module]] are the same
Module Record and exportName is r.[[ExportName]], thenAssert : This is a circular import request.- Return
null .
- If module and r.[[Module]] are the same
- Append the
Record { [[Module]]: module, [[ExportName]]: exportName } to resolveSet. - For each
ExportEntry Record e of module.[[LocalExportEntries]], do- If e.[[ExportName]] is exportName, then
Assert : module provides the direct binding for this export.- Return
ResolvedBinding Record { [[Module]]: module, [[BindingName]]: e.[[LocalName]] }.
- If e.[[ExportName]] is exportName, then
- For each
ExportEntry Record e of module.[[IndirectExportEntries]], do- If e.[[ExportName]] is exportName, then
Assert : e.[[ModuleRequest]] is notnull .- Let importedModule be
GetImportedModule (module, e.[[ModuleRequest]]). - If e.[[ImportName]] is
all , thenAssert : module does not provide the direct binding for this export.- Return
ResolvedBinding Record { [[Module]]: importedModule, [[BindingName]]:namespace }.
- Else,
Assert : module imports a specific binding for this export.Assert : e.[[ImportName]]is a String .- Return importedModule.ResolveExport(e.[[ImportName]], resolveSet).
- If e.[[ExportName]] is exportName, then
- If exportName is
"default" , thenAssert : Adefaultexport was not explicitly defined by this module.- Return
null . - NOTE: A
defaultexport cannot be provided by anexport * from "mod"declaration.
- Let starResolution be
null . - For each
ExportEntry Record e of module.[[StarExportEntries]], doAssert : e.[[ModuleRequest]] is notnull .- Let importedModule be
GetImportedModule (module, e.[[ModuleRequest]]). - Let resolution be importedModule.ResolveExport(exportName, resolveSet).
- If resolution is
ambiguous , returnambiguous . - If resolution is not
null , thenAssert : resolution is aResolvedBinding Record .- If starResolution is
null , then- Set starResolution to resolution.
- Else,
Assert : There is more than one*import that includes the requested name.- If resolution.[[Module]] and starResolution.[[Module]] are not the same
Module Record , returnambiguous . - If resolution.[[BindingName]] is not starResolution.[[BindingName]] and either resolution.[[BindingName]] or starResolution.[[BindingName]] is
namespace , returnambiguous . - If resolution.[[BindingName]]
is a String , starResolution.[[BindingName]]is a String , and resolution.[[BindingName]] is not starResolution.[[BindingName]], returnambiguous .
- Return starResolution.
16.2.1.7.4 InitializeEnvironment ( )
The InitializeEnvironment concrete method of a
- For each
ExportEntry Record e of module.[[IndirectExportEntries]], doAssert : e.[[ExportName]] is notnull .- Let resolution be module.ResolveExport(e.[[ExportName]]).
- If resolution is either
null orambiguous , throw aSyntaxError exception. Assert : resolution is aResolvedBinding Record .
Assert : All named exports from module are resolvable.- Let realm be module.[[Realm]].
Assert : realm is notundefined .- Let env be
NewModuleEnvironment (realm.[[GlobalEnv]]). - Set module.[[Environment]] to env.
- For each
ImportEntry Record in of module.[[ImportEntries]], do- Let importedModule be
GetImportedModule (module, in.[[ModuleRequest]]). - If in.[[ImportName]] is
namespace-object , then- Let namespace be
GetModuleNamespace (importedModule). - Perform ! env.CreateImmutableBinding(in.[[LocalName]],
true ). - Perform ! env.InitializeBinding(in.[[LocalName]], namespace).
- Let namespace be
- Else,
- Let resolution be importedModule.ResolveExport(in.[[ImportName]]).
- If resolution is either
null orambiguous , throw aSyntaxError exception. - If resolution.[[BindingName]] is
namespace , then- Let namespace be
GetModuleNamespace (resolution.[[Module]]). - Perform ! env.CreateImmutableBinding(in.[[LocalName]],
true ). - Perform ! env.InitializeBinding(in.[[LocalName]], namespace).
- Let namespace be
- Else,
- Perform
CreateImportBinding (env, in.[[LocalName]], resolution.[[Module]], resolution.[[BindingName]]).
- Perform
- Let importedModule be
- Let moduleContext be a new
ECMAScript code execution context . - Set the Function of moduleContext to
null . Assert : module.[[Realm]] is notundefined .- Set the
Realm of moduleContext to module.[[Realm]]. - Set the ScriptOrModule of moduleContext to module.
- Set the VariableEnvironment of moduleContext to module.[[Environment]].
- Set the LexicalEnvironment of moduleContext to module.[[Environment]].
- Set the PrivateEnvironment of moduleContext to
null . - Set module.[[Context]] to moduleContext.
- Push moduleContext onto the
execution context stack ; moduleContext is now therunning execution context . - Let code be module.[[ECMAScriptCode]].
- Let varDeclarations be the
VarScopedDeclarations of code. - Let declaredVarNames be a new empty
List . - For each element d of varDeclarations, do
- For each element dn of the
BoundNames of d, do- If declaredVarNames does not contain dn, then
- Perform ! env.CreateMutableBinding(dn,
false ). - Perform ! env.InitializeBinding(dn,
undefined ). - Append dn to declaredVarNames.
- Perform ! env.CreateMutableBinding(dn,
- If declaredVarNames does not contain dn, then
- For each element dn of the
- Let lexDeclarations be the
LexicallyScopedDeclarations of code. - Let privateEnv be
null . - For each element d of lexDeclarations, do
- For each element dn of the
BoundNames of d, do- If
IsConstantDeclaration of d istrue , then- Perform ! env.CreateImmutableBinding(dn,
true ).
- Perform ! env.CreateImmutableBinding(dn,
- Else,
- Perform ! env.CreateMutableBinding(dn,
false ).
- Perform ! env.CreateMutableBinding(dn,
- If d is either a
FunctionDeclaration , aGeneratorDeclaration , anAsyncFunctionDeclaration , or anAsyncGeneratorDeclaration , then- Let fo be
InstantiateFunctionObject of d with arguments env and privateEnv. - Perform ! env.InitializeBinding(dn, fo).
- Let fo be
- If
- For each element dn of the
- Remove moduleContext from the
execution context stack . - Return
unused .
16.2.1.7.5 ExecuteModule ( [ capability ] )
The ExecuteModule concrete method of a
- Let moduleContext be a new
ECMAScript code execution context . - Set the Function of moduleContext to
null . - Set the
Realm of moduleContext to module.[[Realm]]. - Set the ScriptOrModule of moduleContext to module.
Assert : module has been linked and declarations in its module environment have been instantiated.- Set the VariableEnvironment of moduleContext to module.[[Environment]].
- Set the LexicalEnvironment of moduleContext to module.[[Environment]].
- Suspend the
running execution context . - If module.[[HasTLA]] is
false , thenAssert : capability is not present.- Push moduleContext onto the
execution context stack ; moduleContext is now therunning execution context . - Let result be
Completion (Evaluation of module.[[ECMAScriptCode]]). - Suspend moduleContext and remove it from the
execution context stack . - Resume the context that is now on the top of the
execution context stack as therunning execution context . - If result is an
abrupt completion , then- Return ? result.
- Else,
Assert : capability is aPromiseCapability Record .- Perform
AsyncBlockStart (capability, module.[[ECMAScriptCode]], moduleContext).
- Return
unused .
16.2.1.8 Synthetic Module Records
A Synthetic Module Record is used to represent information about a module that is defined by specifications. Its exported names are statically defined at creation, while their corresponding values can change over time using
In addition to the fields defined in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[ExportNames]] | a |
The names of the exports of the module. This list does not contain duplicates. |
| [[EvaluationSteps]] | an |
The initialization logic to perform upon evaluation of the module, taking the |
16.2.1.8.1 CreateDefaultExportSyntheticModule ( defaultExport )
The abstract operation CreateDefaultExportSyntheticModule takes argument defaultExport (an
- Let realm be
the current Realm Record . - Let setDefaultExport be a new
Abstract Closure with parameters (module) that captures defaultExport and performs the following steps when called:- Perform
SetSyntheticModuleExport (module,"default" , defaultExport). - Return
NormalCompletion (unused ).
- Perform
- Return the
Synthetic Module Record { [[Realm]]: realm, [[Environment]]:empty , [[Namespace]]:empty , [[HostDefined]]:undefined , [[ExportNames]]: «"default" », [[EvaluationSteps]]: setDefaultExport }.
16.2.1.8.2 ParseJSONModule ( source )
The abstract operation ParseJSONModule takes argument source (a String) and returns either a
- Let json be ?
ParseJSON (source). - Return
CreateDefaultExportSyntheticModule (json).
16.2.1.8.3 SetSyntheticModuleExport ( module, exportName, exportValue )
The abstract operation SetSyntheticModuleExport takes arguments module (a
16.2.1.8.4 Implementation of Module Record Abstract Methods
The following are the concrete methods for
16.2.1.8.4.1 LoadRequestedModules ( )
The LoadRequestedModules concrete method of a
- Return !
PromiseResolve (%Promise% ,undefined ).
16.2.1.8.4.2 GetExportedNames ( )
The GetExportedNames concrete method of a
- Return module.[[ExportNames]].
16.2.1.8.4.3 ResolveExport ( exportName )
The ResolveExport concrete method of a
- If module.[[ExportNames]] does not contain exportName, return
null . - Return
ResolvedBinding Record { [[Module]]: module, [[BindingName]]: exportName }.
16.2.1.8.4.4 Link ( )
The Link concrete method of a
- Let realm be module.[[Realm]].
- Let env be
NewModuleEnvironment (realm.[[GlobalEnv]]). - Set module.[[Environment]] to env.
- For each String exportName of module.[[ExportNames]], do
- Perform ! env.CreateMutableBinding(exportName,
false ). - Perform ! env.InitializeBinding(exportName,
undefined ).
- Perform ! env.CreateMutableBinding(exportName,
- Return
NormalCompletion (unused ).
16.2.1.8.4.5 Evaluate ( )
The Evaluate concrete method of a
- Let moduleContext be a new
ECMAScript code execution context . - Set the Function of moduleContext to
null . - Set the
Realm of moduleContext to module.[[Realm]]. - Set the ScriptOrModule of moduleContext to module.
- Set the VariableEnvironment of moduleContext to module.[[Environment]].
- Set the LexicalEnvironment of moduleContext to module.[[Environment]].
- Suspend the
running execution context . - Push moduleContext onto the
execution context stack ; moduleContext is now therunning execution context . - Let steps be module.[[EvaluationSteps]].
- Let result be
Completion (steps(module)). - Suspend moduleContext and remove it from the
execution context stack . - Resume the context that is now on the top of the
execution context stack as therunning execution context . - Let pc be !
NewPromiseCapability (%Promise% ). IfAbruptRejectPromise (result, pc).- Perform !
Call (pc.[[Resolve]],undefined , «undefined »). - Return pc.[[Promise]].
16.2.1.9 GetImportedModule ( referrer, request )
The abstract operation GetImportedModule takes arguments referrer (a
- Let records be a
List consisting of eachLoadedModuleRequest Record r of referrer.[[LoadedModules]] such thatModuleRequestsEqual (r, request) istrue . Assert : records has exactly one element, since LoadRequestedModules has completed successfully on referrer prior to invoking this abstract operation.- Let record be the sole element of records.
- Return record.[[Module]].
16.2.1.10 HostLoadImportedModule ( referrer, moduleRequest, hostDefined, payload )
The
An example of when referrer can be a
<button type="button" onclick="import('./foo.mjs')">Click me</button>there will be no import()
An implementation of HostLoadImportedModule must conform to the following requirements:
-
The
host environment must performFinishLoadingImportedModule (referrer, moduleRequest, payload, result), where result is either anormal completion containing the loadedModule Record or athrow completion , either synchronously or asynchronously. -
If this operation is called multiple times with two (referrer, moduleRequest) pairs such that:
- the first referrer is the same as the second referrer;
ModuleRequestsEqual (the first moduleRequest, the second moduleRequest) istrue ;
and it performs
FinishLoadingImportedModule (referrer, moduleRequest, payload, result) where result is anormal completion , then it must performFinishLoadingImportedModule (referrer, moduleRequest, payload, result) with the same result each time. -
If moduleRequest.[[Attributes]] has an entry entry such that entry.[[Key]] is
"type" and entry.[[Value]] is"json" , when thehost environment performsFinishLoadingImportedModule (referrer, moduleRequest, payload, result), result must either be theCompletion Record returned by an invocation ofParseJSONModule or athrow completion . -
The operation must treat payload as an opaque value to be passed through to
FinishLoadingImportedModule .
The actual process performed is
16.2.1.11 FinishLoadingImportedModule ( referrer, moduleRequest, payload, result )
The abstract operation FinishLoadingImportedModule takes arguments referrer (a
- If result is a
normal completion , then- If referrer.[[LoadedModules]] contains a
LoadedModuleRequest Record record such thatModuleRequestsEqual (record, moduleRequest) istrue , thenAssert : record.[[Module]] and result.[[Value]] are the sameModule Record .
- Else,
- Append the
LoadedModuleRequest Record { [[Specifier]]: moduleRequest.[[Specifier]], [[Attributes]]: moduleRequest.[[Attributes]], [[Module]]: result.[[Value]] } to referrer.[[LoadedModules]].
- Append the
- If referrer.[[LoadedModules]] contains a
- If payload is a
GraphLoadingState Record , then- Perform
ContinueModuleLoading (payload, result).
- Perform
- Else,
- Perform
ContinueDynamicImport (payload, result).
- Perform
- Return
unused .
16.2.1.12 AllImportAttributesSupported ( attributes )
The abstract operation AllImportAttributesSupported takes argument attributes (a
- Let supported be
HostGetSupportedImportAttributes (). - For each
ImportAttribute Record attribute of attributes, do- If supported does not contain attribute.[[Key]], return
false .
- If supported does not contain attribute.[[Key]], return
- Return
true .
16.2.1.12.1 HostGetSupportedImportAttributes ( )
The
An implementation of HostGetSupportedImportAttributes must conform to the following requrements:
- It must return a
List of Strings, each indicating a supported attribute. - Each time this operation is called, it must return the same
List with the same contents in the same order.
The default implementation of HostGetSupportedImportAttributes is to return a new empty
16.2.1.13 GetModuleNamespace ( module )
The abstract operation GetModuleNamespace takes argument module (an instance of a concrete subclass of
Assert : If module is aCyclic Module Record , then module.[[Status]] is notnew orunlinked .- Let namespace be module.[[Namespace]].
- If namespace is
empty , then- Let exportedNames be module.GetExportedNames().
- Let unambiguousNames be a new empty
List . - For each element name of exportedNames, do
- Let resolution be module.ResolveExport(name).
- If resolution is a
ResolvedBinding Record , append name to unambiguousNames.
- Set namespace to
ModuleNamespaceCreate (module, unambiguousNames).
- Return namespace.
GetModuleNamespace never throws. Instead, unresolvable names are simply excluded from the namespace at this point. They will lead to a real linking error later unless they are all ambiguous star exports that are not explicitly requested anywhere.
16.2.1.14 Runtime Semantics: Evaluation
- Return
undefined .
- Let result be
Completion (Evaluation ofModuleItemList ). - If result is a
normal completion and result.[[Value]] isempty , then- Return
undefined .
- Return
- Return ? result.
- Let sl be ?
Evaluation ofModuleItemList . - Let s be
Completion (Evaluation ofModuleItem ). - Return ?
UpdateEmpty (s, sl).
The value of a
- Return
empty .
16.2.2 Imports
Syntax
16.2.2.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
BoundNames ofImportDeclaration contains any duplicate entries.
-
It is a Syntax Error if
WithClauseToAttributes ofWithClause has two different entries a and b such that a.[[Key]] is b.[[Key]].
16.2.2.2 Static Semantics: ImportEntries
The
- Return a new empty
List .
- Let entries1 be the
ImportEntries ofModuleItemList . - Let entries2 be the
ImportEntries ofModuleItem . - Return the
list-concatenation of entries1 and entries2.
- Return a new empty
List .
- Let module be the sole element of the
ModuleRequests ofImportDeclaration . - Return the
ImportEntriesForModule ofImportClause with argument module.
- Return a new empty
List .
16.2.2.3 Static Semantics: ImportEntriesForModule
The
- Let entries1 be the
ImportEntriesForModule ofImportedDefaultBinding with argument module. - Let entries2 be the
ImportEntriesForModule ofNameSpaceImport with argument module. - Return the
list-concatenation of entries1 and entries2.
- Let entries1 be the
ImportEntriesForModule ofImportedDefaultBinding with argument module. - Let entries2 be the
ImportEntriesForModule ofNamedImports with argument module. - Return the
list-concatenation of entries1 and entries2.
- Let localName be the sole element of the
BoundNames ofImportedBinding . - Let defaultEntry be the
ImportEntry Record { [[ModuleRequest]]: module, [[ImportName]]:"default" , [[LocalName]]: localName }. - Return « defaultEntry ».
- Let localName be the
StringValue ofImportedBinding . - Let entry be the
ImportEntry Record { [[ModuleRequest]]: module, [[ImportName]]:namespace-object , [[LocalName]]: localName }. - Return « entry ».
- Return a new empty
List .
- Let specs1 be the
ImportEntriesForModule ofImportsList with argument module. - Let specs2 be the
ImportEntriesForModule ofImportSpecifier with argument module. - Return the
list-concatenation of specs1 and specs2.
- Let localName be the sole element of the
BoundNames ofImportedBinding . - Let entry be the
ImportEntry Record { [[ModuleRequest]]: module, [[ImportName]]: localName, [[LocalName]]: localName }. - Return « entry ».
- Let importName be the
StringValue ofModuleExportName . - Let localName be the
StringValue ofImportedBinding . - Let entry be the
ImportEntry Record { [[ModuleRequest]]: module, [[ImportName]]: importName, [[LocalName]]: localName }. - Return « entry ».
16.2.2.4 Static Semantics: WithClauseToAttributes
The
- Return a new empty
List .
- Let attributes be
WithClauseToAttributes ofWithEntries . - Sort attributes according to the lexicographic order of their [[Key]] field, treating the value of each such field as a sequence of UTF-16 code unit values. NOTE: This sorting is observable only in that
hosts are prohibited from changing behaviour based on the order in which attributes are enumerated. - Return attributes.
- Let key be the
PropName ofAttributeKey . - Let entry be the
ImportAttribute Record { [[Key]]: key, [[Value]]: theSV ofStringLiteral }. - Return « entry ».
- Let key be the
PropName ofAttributeKey . - Let entry be the
ImportAttribute Record { [[Key]]: key, [[Value]]: theSV ofStringLiteral }. - Let rest be
WithClauseToAttributes ofWithEntries . - Return the
list-concatenation of « entry » and rest.
16.2.3 Exports
Syntax
16.2.3.1 Static Semantics: Early Errors
-
It is a Syntax Error if the
ReferencedBindings ofNamedExports contains anyStringLiteral s. -
For each
IdentifierName n in theReferencedBindings ofNamedExports : It is a Syntax Error if theStringValue of n is aReservedWord or theStringValue of n is one of"implements" ,"interface" ,"let" ,"package" ,"private" ,"protected" ,"public" , or"static" .
The above rule means that each
16.2.3.2 Static Semantics: ExportedBindings
The
ExportedBindings are the locally bound names that are explicitly associated with a
It is defined piecewise over the following productions:
- Let names1 be the
ExportedBindings ofModuleItemList . - Let names2 be the
ExportedBindings ofModuleItem . - Return the
list-concatenation of names1 and names2.
- Return a new empty
List .
- Return a new empty
List .
- Return the
ExportedBindings ofNamedExports .
- Return the
BoundNames ofVariableStatement .
- Return the
BoundNames ofDeclaration .
- Return the
BoundNames of thisExportDeclaration .
- Return a new empty
List .
- Let names1 be the
ExportedBindings ofExportsList . - Let names2 be the
ExportedBindings ofExportSpecifier . - Return the
list-concatenation of names1 and names2.
- Return a
List whose sole element is theStringValue ofModuleExportName .
- Return a
List whose sole element is theStringValue of the firstModuleExportName .
16.2.3.3 Static Semantics: ExportedNames
The
ExportedNames are the externally visible names that a
It is defined piecewise over the following productions:
- Let names1 be the
ExportedNames ofModuleItemList . - Let names2 be the
ExportedNames ofModuleItem . - Return the
list-concatenation of names1 and names2.
- Return the
ExportedNames ofExportDeclaration .
- Return a new empty
List .
- Return the
ExportedNames ofExportFromClause .
- Return a new empty
List .
- Return a
List whose sole element is theStringValue ofModuleExportName .
- Return the
ExportedNames ofNamedExports .
- Return the
BoundNames ofVariableStatement .
- Return the
BoundNames ofDeclaration .
- Return «
"default" ».
- Return a new empty
List .
- Let names1 be the
ExportedNames ofExportsList . - Let names2 be the
ExportedNames ofExportSpecifier . - Return the
list-concatenation of names1 and names2.
- Return a
List whose sole element is theStringValue ofModuleExportName .
- Return a
List whose sole element is theStringValue of the secondModuleExportName .
16.2.3.4 Static Semantics: ExportEntries
The
- Return a new empty
List .
- Let entries1 be the
ExportEntries ofModuleItemList . - Let entries2 be the
ExportEntries ofModuleItem . - Return the
list-concatenation of entries1 and entries2.
- Return a new empty
List .
- Let module be the sole element of the
ModuleRequests ofExportDeclaration . - Return the
ExportEntriesForModule ofExportFromClause with argument module.
- Return the
ExportEntriesForModule ofNamedExports with argumentnull .
- Let entries be a new empty
List . - Let names be the
BoundNames ofVariableStatement . - For each element name of names, do
- Append the
ExportEntry Record { [[ModuleRequest]]:null , [[ImportName]]:null , [[LocalName]]: name, [[ExportName]]: name } to entries.
- Append the
- Return entries.
- Let entries be a new empty
List . - Let names be the
BoundNames ofDeclaration . - For each element name of names, do
- Append the
ExportEntry Record { [[ModuleRequest]]:null , [[ImportName]]:null , [[LocalName]]: name, [[ExportName]]: name } to entries.
- Append the
- Return entries.
- Let names be the
BoundNames ofHoistableDeclaration . - Let localName be the sole element of names.
- Return a
List whose sole element is a newExportEntry Record { [[ModuleRequest]]:null , [[ImportName]]:null , [[LocalName]]: localName, [[ExportName]]:"default" }.
- Let names be the
BoundNames ofClassDeclaration . - Let localName be the sole element of names.
- Return a
List whose sole element is a newExportEntry Record { [[ModuleRequest]]:null , [[ImportName]]:null , [[LocalName]]: localName, [[ExportName]]:"default" }.
- Let entry be the
ExportEntry Record { [[ModuleRequest]]:null , [[ImportName]]:null , [[LocalName]]:"*default*" , [[ExportName]]:"default" }. - Return « entry ».
16.2.3.5 Static Semantics: ExportEntriesForModule
The
- Let entry be the
ExportEntry Record { [[ModuleRequest]]: module, [[ImportName]]:all-but-default , [[LocalName]]:null , [[ExportName]]:null }. - Return « entry ».
- Let exportName be the
StringValue ofModuleExportName . - Let entry be the
ExportEntry Record { [[ModuleRequest]]: module, [[ImportName]]:all , [[LocalName]]:null , [[ExportName]]: exportName }. - Return « entry ».
- Return a new empty
List .
- Let specs1 be the
ExportEntriesForModule ofExportsList with argument module. - Let specs2 be the
ExportEntriesForModule ofExportSpecifier with argument module. - Return the
list-concatenation of specs1 and specs2.
- Let sourceName be the
StringValue ofModuleExportName . - If module is
null , then- Let localName be sourceName.
- Let importName be
null .
- Else,
- Let localName be
null . - Let importName be sourceName.
- Let localName be
- Return a
List whose sole element is a newExportEntry Record { [[ModuleRequest]]: module, [[ImportName]]: importName, [[LocalName]]: localName, [[ExportName]]: sourceName }.
- Let sourceName be the
StringValue of the firstModuleExportName . - Let exportName be the
StringValue of the secondModuleExportName . - If module is
null , then- Let localName be sourceName.
- Let importName be
null .
- Else,
- Let localName be
null . - Let importName be sourceName.
- Let localName be
- Return a
List whose sole element is a newExportEntry Record { [[ModuleRequest]]: module, [[ImportName]]: importName, [[LocalName]]: localName, [[ExportName]]: exportName }.
16.2.3.6 Static Semantics: ReferencedBindings
The
- Return a new empty
List .
- Let names1 be the
ReferencedBindings ofExportsList . - Let names2 be the
ReferencedBindings ofExportSpecifier . - Return the
list-concatenation of names1 and names2.
- Return the
ReferencedBindings of the firstModuleExportName .
- Return a
List whose sole element is theIdentifierName .
- Return a
List whose sole element is theStringLiteral .
16.2.3.7 Runtime Semantics: Evaluation
- Return
empty .
- Return ?
Evaluation ofVariableStatement .
- Return ?
Evaluation ofDeclaration .
- Return ?
Evaluation ofHoistableDeclaration .
- Let value be ?
BindingClassDeclarationEvaluation ofClassDeclaration . - Let className be the sole element of the
BoundNames ofClassDeclaration . - If className is
"*default*" , then- Let env be the
running execution context 's LexicalEnvironment. - Perform ?
InitializeBoundName ("*default*" , value, env).
- Let env be the
- Return
empty .
- If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue , then- Let value be ?
NamedEvaluation ofAssignmentExpression with argument"default" .
- Let value be ?
- Else,
- Let rhs be ?
Evaluation ofAssignmentExpression . - Let value be ?
GetValue (rhs).
- Let rhs be ?
- Let env be the
running execution context 's LexicalEnvironment. - Perform ?
InitializeBoundName ("*default*" , value, env). - Return
empty .
17 Error Handling and Language Extensions
An implementation must report most errors at the time the relevant ECMAScript language construct is evaluated. An early error is an error that can be detected and reported prior to the evaluation of any construct in the eval is called and prevent evaluation of the eval code. All errors that are not
An implementation must report as an
An implementation shall not treat other kinds of errors as
An implementation shall report all errors as specified, except for the following:
-
Except as restricted in
17.1 , ahost or implementation may extendScript syntax,Module syntax, and regular expression pattern or flag syntax. To permit this, all operations (such as callingeval, using a regular expression literal, or using the Function or RegExpconstructor ) that are allowed to throwSyntaxError are permitted to exhibithost-defined behaviour instead of throwingSyntaxError when they encounter ahost-defined extension to the script syntax or regular expression pattern or flag syntax. -
Except as restricted in
17.1 , ahost or implementation may provide additional types, values, objects, properties, and functions beyond those described in this specification. This may cause constructs (such as looking up a variable in the global scope) to havehost-defined behaviour instead of throwing an error (such asReferenceError ).
17.1 Forbidden Extensions
An implementation must not extend this specification in the following ways:
-
ECMAScript
function objects defined using syntacticconstructors instrict mode code must not be created with own properties named"caller" or"arguments" . Such own properties also must not be created forfunction objects defined using anArrowFunction ,MethodDefinition ,GeneratorDeclaration ,GeneratorExpression ,AsyncGeneratorDeclaration ,AsyncGeneratorExpression ,ClassDeclaration ,ClassExpression ,AsyncFunctionDeclaration ,AsyncFunctionExpression , orAsyncArrowFunction regardless of whether the definition is contained instrict mode code . Built-in functions,strict functions created using the Functionconstructor , generator functions created using the Generatorconstructor , async functions created using the AsyncFunctionconstructor , and functions created using thebindmethod also must not be created with such own properties. -
If an implementation extends any
function object with an own property named"caller" the value of that property, as observed using [[Get]] or [[GetOwnProperty]], must not be astrict function object. If it is anaccessor property , the function that is the value of the property's [[Get]] attribute must never return astrict function when called. -
Neither mapped nor unmapped arguments objects may be created with an own property named
"caller" . -
The behaviour of built-in methods which are specified in ECMA-402, such as those named
toLocaleString, must not be extended except as specified in ECMA-402. -
The RegExp pattern grammars in
22.2.1 andB.1.2 must not be extended to recognize any of the source characters A-Z or a-z asIdentityEscape when the [UnicodeMode] grammar parameter is present.[+UnicodeMode] -
The Syntactic Grammar must not be extended in any manner that allows the token
:to immediately follow source text that is matched by theBindingIdentifier nonterminal symbol. -
When processing
strict mode code , an implementation must not relax theearly error rules of12.9.3.1 . -
TemplateEscapeSequence must not be extended to includeLegacyOctalEscapeSequence orNonOctalDecimalEscapeSequence as defined in12.9.4 . -
When processing
strict mode code , the extensions defined inB.3.1 ,B.3.2 ,B.3.3 , andB.3.5 must not be supported. -
When parsing for the
Module goal symbol , the lexical grammar extensions defined inB.1.1 must not be supported. -
ImportCall must not be extended.
18 ECMAScript Standard Built-in Objects
There are certain built-in objects available whenever an ECMAScript
Unless specified otherwise, a built-in object that is callable as a function is a built-in
Many built-in objects are functions: they can be invoked with arguments. Some of them furthermore are new operator. For each built-in function, this specification describes the arguments required by that function and the properties of that new expression that invokes that
Unless otherwise specified in the description of a particular function, if a built-in function or
Unless otherwise specified in the description of a particular function, if a built-in function or
Implementations that add additional capabilities to the set of built-in functions are encouraged to do so by adding new functions rather than adding new parameters to existing functions.
Unless otherwise specified every built-in function and every built-in Function.prototype (
Unless otherwise specified every built-in prototype object has the Object.prototype (
If this specification defines a built-in
Built-in
Built-in
Each built-in function defined in this specification is created by calling the
Every built-in
For example, the
Unless otherwise specified, the
Every built-in
The value of the
Unless otherwise specified, the
Every other
Every
19 The Global Object
The global object:
- is created before control enters any
execution context . - does not have a [[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a [[Call]] internal method; it cannot be invoked as a function.
- has a [[Prototype]] internal slot whose value is
host-defined . - may have
host-defined properties in addition to the properties defined in this specification. This may include a property whose value is the global object itself.
19.1 Value Properties of the Global Object
19.1.1 globalThis
The initial value of the
This property has the attributes { [[Writable]]:
19.1.2 Infinity
The value of Infinity is
19.1.3 NaN
The value of NaN is
19.1.4 undefined
The value of undefined is
19.2 Function Properties of the Global Object
19.2.1 eval ( x )
This function is the %eval% intrinsic object.
It performs the following steps when called:
- Return ?
PerformEval (x,false ,false ).
19.2.1.1 PerformEval ( x, strictCaller, direct )
The abstract operation PerformEval takes arguments x (an
Assert : If direct isfalse , then strictCaller is alsofalse .- If x
is not a String , return x. - Let evalRealm be
the current Realm Record . - NOTE: In the case of a
direct eval , evalRealm is therealm of both the caller ofevaland of theevalfunction itself. - Perform ?
HostEnsureCanCompileStrings (evalRealm, « », x, direct). - Let inFunction be
false . - Let inMethod be
false . - Let inDerivedConstructor be
false . - Let inClassFieldInitializer be
false . - If direct is
true , then- Let thisEnvRec be
GetThisEnvironment (). - If thisEnvRec is a
Function Environment Record , then- Let F be thisEnvRec.[[FunctionObject]].
- Set inFunction to
true . - Set inMethod to thisEnvRec.HasSuperBinding().
- If F.[[ConstructorKind]] is
derived , set inDerivedConstructor totrue . - Let classFieldInitializerName be F.[[ClassFieldInitializerName]].
- If classFieldInitializerName is not
empty , set inClassFieldInitializer totrue .
- Let thisEnvRec be
- Perform the following substeps in an
implementation-defined order, possibly interleaving parsing and error detection:- Let script be
ParseText (x,Script ). - If script is a
List of errors, throw aSyntaxError exception. - If script
Contains ScriptBody isfalse , returnundefined . - Let body be the
ScriptBody of script. - If inFunction is
false and bodyContains NewTarget , throw aSyntaxError exception. - If inMethod is
false and bodyContains SuperProperty , throw aSyntaxError exception. - If inDerivedConstructor is
false and bodyContains SuperCall , throw aSyntaxError exception. - If inClassFieldInitializer is
true andContainsArguments of body istrue , throw aSyntaxError exception.
- Let script be
- If strictCaller is
true , let strictEval betrue . - Else, let strictEval be
ScriptIsStrict of script. - Let runningContext be the
running execution context . - NOTE: If direct is
true , runningContext will be theexecution context that performed thedirect eval . If direct isfalse , runningContext will be theexecution context for the invocation of theevalfunction. - If direct is
true , then- Let lexEnv be
NewDeclarativeEnvironment (runningContext's LexicalEnvironment). - Let varEnv be runningContext's VariableEnvironment.
- Let privateEnv be runningContext's PrivateEnvironment.
- Let lexEnv be
- Else,
- Let lexEnv be
NewDeclarativeEnvironment (evalRealm.[[GlobalEnv]]). - Let varEnv be evalRealm.[[GlobalEnv]].
- Let privateEnv be
null .
- Let lexEnv be
- If strictEval is
true , set varEnv to lexEnv. - If runningContext is not already suspended, suspend runningContext.
- Let evalContext be a new
ECMAScript code execution context . - Set evalContext's Function to
null . - Set evalContext's
Realm to evalRealm. - Set evalContext's ScriptOrModule to runningContext's ScriptOrModule.
- Set evalContext's VariableEnvironment to varEnv.
- Set evalContext's LexicalEnvironment to lexEnv.
- Set evalContext's PrivateEnvironment to privateEnv.
- Push evalContext onto the
execution context stack ; evalContext is now therunning execution context . - Let result be
Completion (EvalDeclarationInstantiation (body, varEnv, lexEnv, privateEnv, strictEval)). - If result is a
normal completion , then- Set result to
Completion (Evaluation of body).
- Set result to
- If result is a
normal completion and result.[[Value]] isempty , then- Set result to
NormalCompletion (undefined ).
- Set result to
- Suspend evalContext and remove it from the
execution context stack . - Resume the context that is now on the top of the
execution context stack as therunning execution context . - Return ? result.
The eval code cannot instantiate variable or function bindings in the variable environment of the calling context that invoked the eval if either the code of the calling context or the eval code is let, const, or class declarations are always instantiated in a new LexicalEnvironment.
19.2.1.2 HostEnsureCanCompileStrings ( calleeRealm, parameterStrings, bodyString, direct )
The
parameterStrings represents the strings that, when using one of the function eval call.
direct signifies whether the evaluation is a
The default implementation of HostEnsureCanCompileStrings is to return
19.2.1.3 EvalDeclarationInstantiation ( body, varEnv, lexEnv, privateEnv, strict )
The abstract operation EvalDeclarationInstantiation takes arguments body (a
- Let varNames be the
VarDeclaredNames of body. - Let varDeclarations be the
VarScopedDeclarations of body. - If strict is
false , then- If varEnv is a
Global Environment Record , then- For each element name of varNames, do
- If
HasLexicalDeclaration (varEnv, name) istrue , throw aSyntaxError exception. - NOTE:
evalwill not create a global var declaration that would be shadowed by a global lexical declaration.
- If
- For each element name of varNames, do
- Let thisEnv be lexEnv.
Assert : The following loop will terminate.- Repeat, while thisEnv and varEnv are not the same
Environment Record ,- If thisEnv
is not an Object Environment Record , then- NOTE: The environment of with statements cannot contain any lexical declaration so it doesn't need to be checked for var/let hoisting conflicts.
- For each element name of varNames, do
- If ! thisEnv.HasBinding(name) is
true , then- Throw a
SyntaxError exception. - NOTE: Annex
B.3.4 defines alternate semantics for the above step.
- Throw a
- NOTE: A
direct eval will not hoist var declaration over a like-named lexical declaration.
- If ! thisEnv.HasBinding(name) is
- Set thisEnv to thisEnv.[[OuterEnv]].
- If thisEnv
- If varEnv is a
- Let privateIdentifiers be a new empty
List . - Let pointer be privateEnv.
- Repeat, while pointer is not
null ,- For each
Private Name binding of pointer.[[Names]], do- If privateIdentifiers does not contain binding.[[Description]], append binding.[[Description]] to privateIdentifiers.
- Set pointer to pointer.[[OuterPrivateEnvironment]].
- For each
- If
AllPrivateIdentifiersValid of body with argument privateIdentifiers isfalse , throw aSyntaxError exception. - Let functionsToInitialize be a new empty
List . - Let declaredFunctionNames be a new empty
List . - For each element d of varDeclarations, in reverse
List order, do- If d is not either a
VariableDeclaration , aForBinding , or aBindingIdentifier , thenAssert : d is either aFunctionDeclaration , aGeneratorDeclaration , anAsyncFunctionDeclaration , or anAsyncGeneratorDeclaration .- NOTE: If there are multiple function declarations for the same name, the last declaration is used.
- Let fn be the sole element of the
BoundNames of d. - If declaredFunctionNames does not contain fn, then
- If varEnv is a
Global Environment Record , then- Let fnDefinable be ?
CanDeclareGlobalFunction (varEnv, fn). - If fnDefinable is
false , throw aTypeError exception.
- Let fnDefinable be ?
- Append fn to declaredFunctionNames.
- Insert d as the first element of functionsToInitialize.
- If varEnv is a
- If d is not either a
- Let declaredVarNames be a new empty
List . - For each element d of varDeclarations, do
- If d is either a
VariableDeclaration , aForBinding , or aBindingIdentifier , then- For each String vn of the
BoundNames of d, do- If declaredFunctionNames does not contain vn, then
- If varEnv is a
Global Environment Record , then- Let vnDefinable be ?
CanDeclareGlobalVar (varEnv, vn). - If vnDefinable is
false , throw aTypeError exception.
- Let vnDefinable be ?
- If declaredVarNames does not contain vn, then
- Append vn to declaredVarNames.
- If varEnv is a
- If declaredFunctionNames does not contain vn, then
- For each String vn of the
- If d is either a
- NOTE: Annex
B.3.2.3 adds additional steps at this point. - NOTE: No abnormal terminations occur after this algorithm step unless varEnv is a
Global Environment Record and theglobal object is aProxy exotic object . - Let lexDeclarations be the
LexicallyScopedDeclarations of body. - For each element d of lexDeclarations, do
- NOTE: Lexically declared names are only instantiated here but not initialized.
- For each element dn of the
BoundNames of d, do- If
IsConstantDeclaration of d istrue , then- Perform ? lexEnv.CreateImmutableBinding(dn,
true ).
- Perform ? lexEnv.CreateImmutableBinding(dn,
- Else,
- Perform ? lexEnv.CreateMutableBinding(dn,
false ).
- Perform ? lexEnv.CreateMutableBinding(dn,
- If
- For each
Parse Node f of functionsToInitialize, do- Let fn be the sole element of the
BoundNames of f. - Let fo be
InstantiateFunctionObject of f with arguments lexEnv and privateEnv. - If varEnv is a
Global Environment Record , then- Perform ?
CreateGlobalFunctionBinding (varEnv, fn, fo,true ).
- Perform ?
- Else,
- Let bindingExists be ! varEnv.HasBinding(fn).
- If bindingExists is
false , then- NOTE: The following invocation cannot return an
abrupt completion because of the validation preceding step14 . - Perform ! varEnv.CreateMutableBinding(fn,
true ). - Perform ! varEnv.InitializeBinding(fn, fo).
- NOTE: The following invocation cannot return an
- Else,
- Perform ! varEnv.SetMutableBinding(fn, fo,
false ).
- Perform ! varEnv.SetMutableBinding(fn, fo,
- Let fn be the sole element of the
- For each String vn of declaredVarNames, do
- If varEnv is a
Global Environment Record , then- Perform ?
CreateGlobalVarBinding (varEnv, vn,true ).
- Perform ?
- Else,
- Let bindingExists be ! varEnv.HasBinding(vn).
- If bindingExists is
false , then- NOTE: The following invocation cannot return an
abrupt completion because of the validation preceding step14 . - Perform ! varEnv.CreateMutableBinding(vn,
true ). - Perform ! varEnv.InitializeBinding(vn,
undefined ).
- NOTE: The following invocation cannot return an
- If varEnv is a
- Return
unused .
An alternative version of this algorithm is described in
19.2.2 isFinite ( number )
This function is the %isFinite% intrinsic object.
It performs the following steps when called:
19.2.3 isNaN ( number )
This function is the %isNaN% intrinsic object.
It performs the following steps when called:
- Let num be ?
ToNumber (number). - If num is
NaN , returntrue . - Otherwise, return
false .
A reliable way for ECMAScript code to test if a value X is X !== X. The result will be X is
19.2.4 parseFloat ( string )
This function produces a Number value dictated by interpretation of the contents of the string argument as a decimal literal.
It is the %parseFloat% intrinsic object.
It performs the following steps when called:
- Let inputString be ?
ToString (string). - Let trimmedString be !
TrimString (inputString,start ). - Let trimmed be
StringToCodePoints (trimmedString). - Let trimmedPrefix be the longest prefix of trimmed that satisfies the syntax of a
StrDecimalLiteral , which might be trimmed itself. If there is no such prefix, returnNaN . - Let parsedNumber be
ParseText (trimmedPrefix,StrDecimalLiteral ). Assert : parsedNumber is aParse Node .- Return the
StringNumericValue of parsedNumber.
This function may interpret only a leading portion of string as a Number value; it ignores any code units that cannot be interpreted as part of the notation of a decimal literal, and no indication is given that any such code units were ignored.
19.2.5 parseInt ( string, radix )
This function produces an
It is the %parseInt% intrinsic object.
It performs the following steps when called:
- Let inputString be ?
ToString (string). - Let S be !
TrimString (inputString,start ). - Let sign be 1.
- If S is not empty and the first code unit of S is the code unit 0x002D (HYPHEN-MINUS), set sign to -1.
- If S is not empty and the first code unit of S is either the code unit 0x002B (PLUS SIGN) or the code unit 0x002D (HYPHEN-MINUS), set S to the
substring of S from index 1. - Let R be
ℝ (?ToInt32 (radix)). - Let stripPrefix be
true . - If R ≠ 0, then
- If R < 2 or R > 36, return
NaN . - If R ≠ 16, set stripPrefix to
false .
- If R < 2 or R > 36, return
- Else,
- Set R to 10.
- If stripPrefix is
true , then- If the length of S is at least 2 and the first two code units of S are either
"0x" or"0X" , then- Set S to the
substring of S from index 2. - Set R to 16.
- Set S to the
- If the length of S is at least 2 and the first two code units of S are either
- If S contains a code unit that is not a radix-R digit, let end be the index within S of the first such code unit; otherwise, let end be the length of S.
- Let Z be the
substring of S from 0 to end. - If Z is empty, return
NaN . - Let mathInt be the
integer value that is represented by Z in radix-R notation, using the letters A through Z and a through z for digits with values 10 through 35. (However, if R = 10 and Z contains more than 20 significant digits, every significant digit after the 20th may be replaced by a 0 digit, at the option of the implementation; and if R is not one of 2, 4, 8, 10, 16, or 32, then mathInt may be animplementation-approximated integer representing theinteger value denoted by Z in radix-R notation.) - If mathInt = 0, then
- If sign = -1, return
-0 𝔽. - Return
+0 𝔽.
- If sign = -1, return
- Return
𝔽 (sign × mathInt).
19.2.6 URI Handling Functions
Uniform Resource Identifiers, or URIs, are Strings that identify resources (e.g. web pages or files) and transport protocols by which to access them (e.g. HTTP or FTP) on the Internet. The ECMAScript language itself does not provide any support for using URIs except for functions that encode and decode URIs as described in this section. encodeURI and decodeURI are intended to work with complete URIs; they assume that any reserved characters are intended to have special meaning (e.g., as delimiters) and so are not encoded. encodeURIComponent and decodeURIComponent are intended to work with the individual components of a URI; they assume that any reserved characters represent text and must be encoded to avoid special meaning when the component is part of a complete URI.
The set of reserved characters is based upon RFC 2396 and does not reflect changes introduced by the more recent RFC 3986.
Many implementations of ECMAScript provide additional functions and methods that manipulate web pages; these functions are beyond the scope of this standard.
19.2.6.1 decodeURI ( encodedURI )
This function computes a new version of a URI in which each escape sequence and UTF-8 encoding of the sort that might be introduced by the encodeURI function is replaced with the UTF-16 encoding of the code point that it represents. Escape sequences that could not have been introduced by encodeURI are not replaced.
It is the %decodeURI% intrinsic object.
It performs the following steps when called:
19.2.6.2 decodeURIComponent ( encodedURIComponent )
This function computes a new version of a URI in which each escape sequence and UTF-8 encoding of the sort that might be introduced by the encodeURIComponent function is replaced with the UTF-16 encoding of the code point that it represents.
It is the %decodeURIComponent% intrinsic object.
It performs the following steps when called:
19.2.6.3 encodeURI ( uri )
This function computes a new version of a UTF-16 encoded (
It is the %encodeURI% intrinsic object.
It performs the following steps when called:
19.2.6.4 encodeURIComponent ( uriComponent )
This function computes a new version of a UTF-16 encoded (
It is the %encodeURIComponent% intrinsic object.
It performs the following steps when called:
19.2.6.5 Encode ( string, extraUnescaped )
The abstract operation Encode takes arguments string (a String) and extraUnescaped (a String) and returns either a
- Let len be the length of string.
- Let R be the empty String.
- Let alwaysUnescaped be the
string-concatenation ofthe ASCII word characters and"-.!~*'()" . - Let unescapedSet be the
string-concatenation of alwaysUnescaped and extraUnescaped. - Let k be 0.
- Repeat, while k < len,
- Let C be the code unit at index k within string.
- If unescapedSet contains C, then
- Set k to k + 1.
- Set R to the
string-concatenation of R and C.
- Else,
- Let cp be
CodePointAt (string, k). - If cp.[[IsUnpairedSurrogate]] is
true , throw aURIError exception. - Set k to k + cp.[[CodeUnitCount]].
- Let Octets be the
List of octets resulting by applying the UTF-8 transformation to cp.[[CodePoint]]. - For each element octet of Octets, do
- Let hex be the String representation of octet, formatted as an uppercase hexadecimal number.
- Set R to the
string-concatenation of R,"%" , andStringPad (hex, 2,"0" ,start ).
- Let cp be
- Return R.
Because percent-encoding is used to represent individual octets, a single code point may be expressed as multiple consecutive escape sequences (one for each of its 8-bit UTF-8 code units).
19.2.6.6 Decode ( string, preserveEscapeSet )
The abstract operation Decode takes arguments string (a String) and preserveEscapeSet (a String) and returns either a
- Let len be the length of string.
- Let R be the empty String.
- Let k be 0.
- Repeat, while k < len,
- Let C be the code unit at index k within string.
- Let S be C.
- If C is the code unit 0x0025 (PERCENT SIGN), then
- If k + 3 > len, throw a
URIError exception. - Let escape be the
substring of string from k to k + 3. - Let B be
ParseHexOctet (string, k + 1). - If B is not an
integer , throw aURIError exception. - Set k to k + 2.
- Let n be the number of leading 1 bits in B.
- If n = 0, then
- Let asciiChar be the code unit whose numeric value is B.
- If preserveEscapeSet contains asciiChar, set S to escape. Otherwise, set S to asciiChar.
- Else,
- If n = 1 or n > 4, throw a
URIError exception. - Let Octets be « B ».
- Let j be 1.
- Repeat, while j < n,
- Set k to k + 1.
- If k + 3 > len, throw a
URIError exception. - If the code unit at index k within string is not the code unit 0x0025 (PERCENT SIGN), throw a
URIError exception. - Let continuationByte be
ParseHexOctet (string, k + 1). - If continuationByte is not an
integer , throw aURIError exception. - Append continuationByte to Octets.
- Set k to k + 2.
- Set j to j + 1.
Assert : The length of Octets is n.- If Octets does not contain a valid UTF-8 encoding of a Unicode code point, throw a
URIError exception. - Let V be the code point obtained by applying the UTF-8 transformation to Octets, that is, from a
List of octets into a 21-bit value. - Set S to
UTF16EncodeCodePoint (V).
- If n = 1 or n > 4, throw a
- If k + 3 > len, throw a
- Set R to the
string-concatenation of R and S. - Set k to k + 1.
- Return R.
RFC 3629 prohibits the decoding of invalid UTF-8 octet sequences. For example, the invalid sequence 0xC0 0x80 must not decode into the code unit 0x0000. Implementations of the Decode algorithm are required to throw a
19.2.6.7 ParseHexOctet ( string, position )
The abstract operation ParseHexOctet takes arguments string (a String) and position (a non-negative
- Let len be the length of string.
Assert : position + 2 ≤ len.- Let hexDigits be the
substring of string from position to position + 2. - Let parseResult be
ParseText (hexDigits,HexDigits ).[~Sep] - If parseResult is not a
Parse Node , return parseResult. - Let n be the MV of parseResult.
Assert : n is in theinclusive interval from 0 to 255.- Return n.
19.3 Constructor Properties of the Global Object
19.3.1 AggregateError ( . . . )
See
19.3.2 Array ( . . . )
See
19.3.3 ArrayBuffer ( . . . )
See
19.3.4 BigInt ( . . . )
See
19.3.5 BigInt64Array ( . . . )
See
19.3.6 BigUint64Array ( . . . )
See
19.3.7 Boolean ( . . . )
See
19.3.8 DataView ( . . . )
See
19.3.9 Date ( . . . )
See
19.3.10 Error ( . . . )
See
19.3.11 EvalError ( . . . )
See
19.3.12 FinalizationRegistry ( . . . )
See
19.3.13 Float16Array ( . . . )
See
19.3.14 Float32Array ( . . . )
See
19.3.15 Float64Array ( . . . )
See
19.3.16 Function ( . . . )
See
19.3.17 Int8Array ( . . . )
See
19.3.18 Int16Array ( . . . )
See
19.3.19 Int32Array ( . . . )
See
19.3.20 Iterator ( . . . )
See
19.3.21 Map ( . . . )
See
19.3.22 Number ( . . . )
See
19.3.23 Object ( . . . )
See
19.3.24 Promise ( . . . )
See
19.3.25 Proxy ( . . . )
See
19.3.26 RangeError ( . . . )
See
19.3.27 ReferenceError ( . . . )
See
19.3.28 RegExp ( . . . )
See
19.3.29 Set ( . . . )
See
19.3.30 SharedArrayBuffer ( . . . )
See
19.3.31 String ( . . . )
See
19.3.32 Symbol ( . . . )
See
19.3.33 SyntaxError ( . . . )
See
19.3.34 TypeError ( . . . )
See
19.3.35 Uint8Array ( . . . )
See
19.3.36 Uint8ClampedArray ( . . . )
See
19.3.37 Uint16Array ( . . . )
See
19.3.38 Uint32Array ( . . . )
See
19.3.39 URIError ( . . . )
See
19.3.40 WeakMap ( . . . )
See
19.3.41 WeakRef ( . . . )
See
19.3.42 WeakSet ( . . . )
See
19.4 Other Properties of the Global Object
19.4.1 Atomics
See
19.4.2 JSON
See
19.4.3 Math
See
19.4.4 Reflect
See
20 Fundamental Objects
20.1 Object Objects
20.1.1 The Object Constructor
The Object
- is %Object%.
- is the initial value of the
"Object" property of theglobal object . - creates a new
ordinary object when called as aconstructor . - performs a type conversion when called as a function rather than as a
constructor . - may be used as the value of an
extendsclause of a class definition.
20.1.1.1 Object ( [ value ] )
This function performs the following steps when called:
- If NewTarget is neither
undefined nor theactive function object , then- Return ?
OrdinaryCreateFromConstructor (NewTarget,"%Object.prototype%" ).
- Return ?
- If value is either
undefined ornull , returnOrdinaryObjectCreate (%Object.prototype% ). - Return !
ToObject (value).
20.1.2 Properties of the Object Constructor
The Object
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"length" property whose value is1 𝔽. - has the following additional properties:
20.1.2.1 Object.assign ( target, ...sources )
This function copies the values of all of the enumerable own properties from one or more source objects to a target object.
It performs the following steps when called:
The
20.1.2.2 Object.create ( O, Properties )
This function creates a new object with a specified prototype.
It performs the following steps when called:
- If O
is not an Object and O is notnull , throw aTypeError exception. - Let obj be
OrdinaryObjectCreate (O). - If Properties is not
undefined , then- Return ?
ObjectDefineProperties (obj, Properties).
- Return ?
- Return obj.
20.1.2.3 Object.defineProperties ( O, Properties )
This function adds own properties and/or updates the attributes of existing own properties of an object.
It performs the following steps when called:
- If O
is not an Object , throw aTypeError exception. - Return ?
ObjectDefineProperties (O, Properties).
20.1.2.3.1 ObjectDefineProperties ( O, Properties )
The abstract operation ObjectDefineProperties takes arguments O (an Object) and Properties (an
- Let props be ?
ToObject (Properties). - Let keys be ? props.[[OwnPropertyKeys]]().
- Let descriptors be a new empty
List . - For each element nextKey of keys, do
- Let propDesc be ? props.[[GetOwnProperty]](nextKey).
- If propDesc is not
undefined and propDesc.[[Enumerable]] istrue , then- Let descObj be ?
Get (props, nextKey). - Let desc be ?
ToPropertyDescriptor (descObj). - Append the
Record { [[Key]]: nextKey, [[Descriptor]]: desc } to descriptors.
- Let descObj be ?
- For each element property of descriptors, do
- Perform ?
DefinePropertyOrThrow (O, property.[[Key]], property.[[Descriptor]]).
- Perform ?
- Return O.
20.1.2.4 Object.defineProperty ( O, P, Attributes )
This function adds an own property and/or updates the attributes of an existing own property of an object.
It performs the following steps when called:
- If O
is not an Object , throw aTypeError exception. - Let key be ?
ToPropertyKey (P). - Let desc be ?
ToPropertyDescriptor (Attributes). - Perform ?
DefinePropertyOrThrow (O, key, desc). - Return O.
20.1.2.5 Object.entries ( O )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let entryList be ?
EnumerableOwnProperties (obj,key+value ). - Return
CreateArrayFromList (entryList).
20.1.2.6 Object.freeze ( O )
This function performs the following steps when called:
- If O
is not an Object , return O. - Let status be ?
SetIntegrityLevel (O,frozen ). - If status is
false , throw aTypeError exception. - Return O.
20.1.2.7 Object.fromEntries ( iterable )
This function performs the following steps when called:
- Perform ?
RequireObjectCoercible (iterable). - Let obj be
OrdinaryObjectCreate (%Object.prototype% ). Assert : obj is an extensibleordinary object with no own properties.- Let closure be a new
Abstract Closure with parameters (key, value) that captures obj and performs the following steps when called:- Let propertyKey be ?
ToPropertyKey (key). - Perform !
CreateDataPropertyOrThrow (obj, propertyKey, value). - Return
undefined .
- Let propertyKey be ?
- Let adder be
CreateBuiltinFunction (closure, 2,"" , « »). - Return ?
AddEntriesFromIterable (obj, iterable, adder).
20.1.2.8 Object.getOwnPropertyDescriptor ( O, P )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let key be ?
ToPropertyKey (P). - Let desc be ? obj.[[GetOwnProperty]](key).
- Return
FromPropertyDescriptor (desc).
20.1.2.9 Object.getOwnPropertyDescriptors ( O )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let ownKeys be ? obj.[[OwnPropertyKeys]]().
- Let descriptors be
OrdinaryObjectCreate (%Object.prototype% ). - For each element key of ownKeys, do
- Let desc be ? obj.[[GetOwnProperty]](key).
- Let descriptor be
FromPropertyDescriptor (desc). - If descriptor is not
undefined , perform !CreateDataPropertyOrThrow (descriptors, key, descriptor).
- Return descriptors.
20.1.2.10 Object.getOwnPropertyNames ( O )
This function performs the following steps when called:
- Return
CreateArrayFromList (?GetOwnPropertyKeys (O,string )).
20.1.2.11 Object.getOwnPropertySymbols ( O )
This function performs the following steps when called:
- Return
CreateArrayFromList (?GetOwnPropertyKeys (O,symbol )).
20.1.2.11.1 GetOwnPropertyKeys ( O, type )
The abstract operation GetOwnPropertyKeys takes arguments O (an
- Let obj be ?
ToObject (O). - Let keys be ? obj.[[OwnPropertyKeys]]().
- Let nameList be a new empty
List . - For each element nextKey of keys, do
- If nextKey
is a Symbol and type issymbol , or if nextKeyis a String and type isstring , then- Append nextKey to nameList.
- If nextKey
- Return nameList.
20.1.2.12 Object.getPrototypeOf ( O )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Return ? obj.[[GetPrototypeOf]]().
20.1.2.13 Object.groupBy ( items, callback )
callback should be a function that accepts two arguments. groupBy calls callback once for each element in items, in ascending order, and constructs a new object. Each value returned by callback is coerced to a
callback is called with two arguments: the value of the element and the index of the element.
The return value of groupBy is an object that does not inherit from
This function performs the following steps when called:
- Let groups be ?
GroupBy (items, callback,property ). - Let obj be
OrdinaryObjectCreate (null ). - For each
Record { [[Key]], [[Elements]] } g of groups, do- Let elements be
CreateArrayFromList (g.[[Elements]]). - Perform !
CreateDataPropertyOrThrow (obj, g.[[Key]], elements).
- Let elements be
- Return obj.
20.1.2.14 Object.hasOwn ( O, P )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let key be ?
ToPropertyKey (P). - Return ?
HasOwnProperty (obj, key).
20.1.2.15 Object.is ( value1, value2 )
This function performs the following steps when called:
- Return
SameValue (value1, value2).
20.1.2.16 Object.isExtensible ( O )
This function performs the following steps when called:
- If O
is not an Object , returnfalse . - Return ?
IsExtensible (O).
20.1.2.17 Object.isFrozen ( O )
This function performs the following steps when called:
- If O
is not an Object , returntrue . - Return ?
TestIntegrityLevel (O,frozen ).
20.1.2.18 Object.isSealed ( O )
This function performs the following steps when called:
- If O
is not an Object , returntrue . - Return ?
TestIntegrityLevel (O,sealed ).
20.1.2.19 Object.keys ( O )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let keyList be ?
EnumerableOwnProperties (obj,key ). - Return
CreateArrayFromList (keyList).
20.1.2.20 Object.preventExtensions ( O )
This function performs the following steps when called:
- If O
is not an Object , return O. - Let status be ? O.[[PreventExtensions]]().
- If status is
false , throw aTypeError exception. - Return O.
20.1.2.21 Object.prototype
The initial value of Object.prototype is the
This property has the attributes { [[Writable]]:
20.1.2.22 Object.seal ( O )
This function performs the following steps when called:
- If O
is not an Object , return O. - Let status be ?
SetIntegrityLevel (O,sealed ). - If status is
false , throw aTypeError exception. - Return O.
20.1.2.23 Object.setPrototypeOf ( O, proto )
This function performs the following steps when called:
- Set O to ?
RequireObjectCoercible (O). - If proto
is not an Object and proto is notnull , throw aTypeError exception. - If O
is not an Object , return O. - Let status be ? O.[[SetPrototypeOf]](proto).
- If status is
false , throw aTypeError exception. - Return O.
20.1.2.24 Object.values ( O )
This function performs the following steps when called:
- Let obj be ?
ToObject (O). - Let valueList be ?
EnumerableOwnProperties (obj,value ). - Return
CreateArrayFromList (valueList).
20.1.3 Properties of the Object Prototype Object
The Object prototype object:
- is %Object.prototype%.
- has an [[Extensible]] internal slot whose value is
true . - has the internal methods defined for
ordinary objects , except for the [[SetPrototypeOf]] method, which is as defined in10.4.7.1 . (Thus, it is animmutable prototype exotic object .) - has a [[Prototype]] internal slot whose value is
null .
20.1.3.1 Object.prototype.constructor
The initial value of Object.prototype.constructor is
20.1.3.2 Object.prototype.hasOwnProperty ( V )
This method performs the following steps when called:
- Let P be ?
ToPropertyKey (V). - Let O be ?
ToObject (this value). - Return ?
HasOwnProperty (O, P).
20.1.3.3 Object.prototype.isPrototypeOf ( V )
This method performs the following steps when called:
- If V
is not an Object , returnfalse . - Let O be ?
ToObject (this value). - Repeat,
- Set V to ? V.[[GetPrototypeOf]]().
- If V is
null , returnfalse . - If
SameValue (O, V) istrue , returntrue .
20.1.3.4 Object.prototype.propertyIsEnumerable ( V )
This method performs the following steps when called:
- Let P be ?
ToPropertyKey (V). - Let O be ?
ToObject (this value). - Let desc be ? O.[[GetOwnProperty]](P).
- If desc is
undefined , returnfalse . - Return desc.[[Enumerable]].
This method does not consider objects in the prototype chain.
20.1.3.5 Object.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )
This method performs the following steps when called:
- Let O be the
this value. - Return ?
Invoke (O,"toString" ).
The optional parameters to this method are not used but are intended to correspond to the parameter pattern used by ECMA-402 toLocaleString methods. Implementations that do not include ECMA-402 support must not use those parameter positions for other purposes.
This method provides a generic toLocaleString implementation for objects that have no locale-sensitive toString behaviour. Array, Number, Date, and toLocaleString methods.
ECMA-402 intentionally does not provide an alternative to this default implementation.
20.1.3.6 Object.prototype.toString ( )
This method performs the following steps when called:
- If the
this value isundefined , return"[object Undefined]" . - If the
this value isnull , return"[object Null]" . - Let O be !
ToObject (this value). - Let isArray be ?
IsArray (O). - If isArray is
true , let builtinTag be"Array" . - Else if O has a [[ParameterMap]] internal slot, let builtinTag be
"Arguments" . - Else if O has a [[Call]] internal method, let builtinTag be
"Function" . - Else if O has an [[ErrorData]] internal slot, let builtinTag be
"Error" . - Else if O has a [[BooleanData]] internal slot, let builtinTag be
"Boolean" . - Else if O has a [[NumberData]] internal slot, let builtinTag be
"Number" . - Else if O has a [[StringData]] internal slot, let builtinTag be
"String" . - Else if O has a [[DateValue]] internal slot, let builtinTag be
"Date" . - Else if O has a [[RegExpMatcher]] internal slot, let builtinTag be
"RegExp" . - Else, let builtinTag be
"Object" . - Let tag be ?
Get (O,%Symbol.toStringTag% ). - If tag
is not a String , set tag to builtinTag. - Return the
string-concatenation of"[object " , tag, and"]" .
Historically, this method was occasionally used to access the String value of the [[Class]] internal slot that was used in previous editions of this specification as a nominal type tag for various built-in objects. The above definition of toString preserves compatibility for legacy code that uses toString as a test for those specific kinds of built-in objects. It does not provide a reliable type testing mechanism for other kinds of built-in or program defined objects. In addition, programs can use
20.1.3.7 Object.prototype.valueOf ( )
This method performs the following steps when called:
- Return ?
ToObject (this value).
20.1.3.8 Object.prototype.__proto__
Object.prototype.__proto__ is an
20.1.3.8.1 get Object.prototype.__proto__
The value of the [[Get]] attribute is a built-in function that requires no arguments. It performs the following steps when called:
- Let O be ?
ToObject (this value). - Return ? O.[[GetPrototypeOf]]().
20.1.3.8.2 set Object.prototype.__proto__
The value of the [[Set]] attribute is a built-in function that takes an argument proto. It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If proto
is not an Object and proto is notnull , returnundefined . - If O
is not an Object , returnundefined . - Let status be ? O.[[SetPrototypeOf]](proto).
- If status is
false , throw aTypeError exception. - Return
undefined .
20.1.3.9 Legacy Object.prototype Accessor Methods
20.1.3.9.1 Object.prototype.__defineGetter__ ( P, getter )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - If
IsCallable (getter) isfalse , throw aTypeError exception. - Let desc be PropertyDescriptor { [[Get]]: getter, [[Enumerable]]:
true , [[Configurable]]:true }. - Let key be ?
ToPropertyKey (P). - Perform ?
DefinePropertyOrThrow (O, key, desc). - Return
undefined .
20.1.3.9.2 Object.prototype.__defineSetter__ ( P, setter )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - If
IsCallable (setter) isfalse , throw aTypeError exception. - Let desc be PropertyDescriptor { [[Set]]: setter, [[Enumerable]]:
true , [[Configurable]]:true }. - Let key be ?
ToPropertyKey (P). - Perform ?
DefinePropertyOrThrow (O, key, desc). - Return
undefined .
20.1.3.9.3 Object.prototype.__lookupGetter__ ( P )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let key be ?
ToPropertyKey (P). - Repeat,
- Let desc be ? O.[[GetOwnProperty]](key).
- If desc is not
undefined , then- If
IsAccessorDescriptor (desc) istrue , return desc.[[Get]]. - Return
undefined .
- If
- Set O to ? O.[[GetPrototypeOf]]().
- If O is
null , returnundefined .
20.1.3.9.4 Object.prototype.__lookupSetter__ ( P )
This method performs the following steps when called:
- Let O be ?
ToObject (this value). - Let key be ?
ToPropertyKey (P). - Repeat,
- Let desc be ? O.[[GetOwnProperty]](key).
- If desc is not
undefined , then- If
IsAccessorDescriptor (desc) istrue , return desc.[[Set]]. - Return
undefined .
- If
- Set O to ? O.[[GetPrototypeOf]]().
- If O is
null , returnundefined .
20.1.4 Properties of Object Instances
Object instances have no special properties beyond those inherited from the
20.2 Function Objects
20.2.1 The Function Constructor
The Function
- is %Function%.
- is the initial value of the
"Function" property of theglobal object . - creates and initializes a new
function object when called as a function rather than as aconstructor . Thus the function callFunction(…)is equivalent to the object creation expressionnew Function(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Function behaviour must include asupercall to the Functionconstructor to create and initialize a subclass instance with the internal slots necessary for built-in function behaviour. All ECMAScript syntactic forms for definingfunction objects create instances of Function. There is no syntactic means to create instances of Function subclasses except for the built-in GeneratorFunction, AsyncFunction, and AsyncGeneratorFunction subclasses.
20.2.1.1 Function ( ...parameterArgs, bodyArg )
The last argument (if any) specifies the body (executable code) of a function; any preceding arguments specify formal parameters.
This function performs the following steps when called:
- Let C be the
active function object . - If bodyArg is not present, set bodyArg to the empty String.
- Return ?
CreateDynamicFunction (C, NewTarget,normal , parameterArgs, bodyArg).
It is permissible but not necessary to have one argument for each formal parameter to be specified. For example, all three of the following expressions produce the same result:
new Function("a", "b", "c", "return a+b+c")
new Function("a, b, c", "return a+b+c")
new Function("a,b", "c", "return a+b+c")20.2.1.1.1 CreateDynamicFunction ( constructor, newTarget, kind, parameterArgs, bodyArg )
The abstract operation CreateDynamicFunction takes arguments constructor (a new was initially applied to. parameterArgs and bodyArg reflect the argument values that were passed to constructor. It performs the following steps when called:
- If newTarget is
undefined , set newTarget to constructor. - If kind is
normal , then- Let prefix be
"function" . - Let exprSym be the grammar symbol
FunctionExpression . - Let bodySym be the grammar symbol
FunctionBody .[~Yield, ~Await] - Let parameterSym be the grammar symbol
FormalParameters .[~Yield, ~Await] - Let fallbackProto be
"%Function.prototype%" .
- Let prefix be
- Else if kind is
generator , then- Let prefix be
"function*" . - Let exprSym be the grammar symbol
GeneratorExpression . - Let bodySym be the grammar symbol
GeneratorBody . - Let parameterSym be the grammar symbol
FormalParameters .[+Yield, ~Await] - Let fallbackProto be
"%GeneratorFunction.prototype%" .
- Let prefix be
- Else if kind is
async , then- Let prefix be
"async function" . - Let exprSym be the grammar symbol
AsyncFunctionExpression . - Let bodySym be the grammar symbol
AsyncFunctionBody . - Let parameterSym be the grammar symbol
FormalParameters .[~Yield, +Await] - Let fallbackProto be
"%AsyncFunction.prototype%" .
- Let prefix be
- Else,
Assert : kind isasync-generator .- Let prefix be
"async function*" . - Let exprSym be the grammar symbol
AsyncGeneratorExpression . - Let bodySym be the grammar symbol
AsyncGeneratorBody . - Let parameterSym be the grammar symbol
FormalParameters .[+Yield, +Await] - Let fallbackProto be
"%AsyncGeneratorFunction.prototype%" .
- Let argCount be the number of elements in parameterArgs.
- Let parameterStrings be a new empty
List . - For each element arg of parameterArgs, do
- Append ?
ToString (arg) to parameterStrings.
- Append ?
- Let bodyString be ?
ToString (bodyArg). - Let currentRealm be
the current Realm Record . - Perform ?
HostEnsureCanCompileStrings (currentRealm, parameterStrings, bodyString,false ). - Let P be the empty String.
- If argCount > 0, then
- Set P to parameterStrings[0].
- Let k be 1.
- Repeat, while k < argCount,
- Let nextArgString be parameterStrings[k].
- Set P to the
string-concatenation of P,"," (a comma), and nextArgString. - Set k to k + 1.
- Let bodyParseString be the
string-concatenation of 0x000A (LINE FEED), bodyString, and 0x000A (LINE FEED). - Let sourceString be the
string-concatenation of prefix," anonymous(" , P, 0x000A (LINE FEED),") {" , bodyParseString, and"}" . - Let sourceText be
StringToCodePoints (sourceString). - Let parameters be
ParseText (P, parameterSym). - If parameters is a
List of errors, throw aSyntaxError exception. - Let body be
ParseText (bodyParseString, bodySym). - If body is a
List of errors, throw aSyntaxError exception. - NOTE: The parameters and body are parsed separately to ensure that each is valid alone. For example,
new Function("/*", "*/ ) {")does not evaluate to a function. - NOTE: If this step is reached, sourceText must have the syntax of exprSym (although the reverse implication does not hold). The purpose of the next two steps is to enforce any Early Error rules which apply to exprSym directly.
- Let expr be
ParseText (sourceText, exprSym). - If expr is a
List of errors, throw aSyntaxError exception. - Let proto be ?
GetPrototypeFromConstructor (newTarget, fallbackProto). - Let env be currentRealm.[[GlobalEnv]].
- Let privateEnv be
null . - Let F be
OrdinaryFunctionCreate (proto, sourceText, parameters, body,non-lexical-this , env, privateEnv). - Perform
SetFunctionName (F,"anonymous" ). - If kind is
generator , then- Let prototype be
OrdinaryObjectCreate (%GeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }).
- Let prototype be
- Else if kind is
async-generator , then- Let prototype be
OrdinaryObjectCreate (%AsyncGeneratorPrototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor { [[Value]]: prototype, [[Writable]]:true , [[Enumerable]]:false , [[Configurable]]:false }).
- Let prototype be
- Else if kind is
normal , then- Perform
MakeConstructor (F).
- Perform
- NOTE: Functions whose kind is
async are not constructable and do not have a [[Construct]] internal method or a"prototype" property. - Return F.
CreateDynamicFunction defines a
20.2.2 Properties of the Function Constructor
The Function
- is itself a built-in
function object . - has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"length" property whose value is1 𝔽. - has the following properties:
20.2.2.1 Function.prototype
The value of Function.prototype is the
This property has the attributes { [[Writable]]:
20.2.3 Properties of the Function Prototype Object
The Function prototype object:
- is %Function.prototype%.
- is itself a built-in
function object . - accepts any arguments and returns
undefined when invoked. - does not have a [[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - has a [[Prototype]] internal slot whose value is
%Object.prototype% . - does not have a
"prototype" property. - has a
"length" property whose value is+0 𝔽. - has a
"name" property whose value is the empty String.
The Function prototype object is specified to be a
20.2.3.1 Function.prototype.apply ( thisArg, argArray )
This method performs the following steps when called:
- Let func be the
this value. - If
IsCallable (func) isfalse , throw aTypeError exception. - If argArray is either
undefined ornull , then- Perform
PrepareForTailCall (). - Return ?
Call (func, thisArg).
- Perform
- Let argList be ?
CreateListFromArrayLike (argArray). - Perform
PrepareForTailCall (). - Return ?
Call (func, thisArg, argList).
The thisArg value is passed without modification as the
If func is either an arrow function or a
20.2.3.2 Function.prototype.bind ( thisArg, ...args )
This method performs the following steps when called:
- Let Target be the
this value. - If
IsCallable (Target) isfalse , throw aTypeError exception. - Let F be ?
BoundFunctionCreate (Target, thisArg, args). - Let L be 0.
- Let targetHasLength be ?
HasOwnProperty (Target,"length" ). - If targetHasLength is
true , then- Let targetLen be ?
Get (Target,"length" ). - If targetLen
is a Number , then- If targetLen is
+∞ 𝔽, then- Set L to +∞.
- Else if targetLen is
-∞ 𝔽, then- Set L to 0.
- Else,
- Let targetLenAsInt be !
ToIntegerOrInfinity (targetLen). Assert : targetLenAsInt isfinite .- Let argCount be the number of elements in args.
- Set L to
max (targetLenAsInt - argCount, 0).
- Let targetLenAsInt be !
- If targetLen is
- Let targetLen be ?
- Perform
SetFunctionLength (F, L). - Let targetName be ?
Get (Target,"name" ). - If targetName
is not a String , set targetName to the empty String. - Perform
SetFunctionName (F, targetName,"bound" ). - Return F.
Function.prototype.bind are
If Target is either an arrow function or a
20.2.3.3 Function.prototype.call ( thisArg, ...args )
This method performs the following steps when called:
- Let func be the
this value. - If
IsCallable (func) isfalse , throw aTypeError exception. - Perform
PrepareForTailCall (). - Return ?
Call (func, thisArg, args).
The thisArg value is passed without modification as the
If func is either an arrow function or a
20.2.3.4 Function.prototype.constructor
The initial value of Function.prototype.constructor is
20.2.3.5 Function.prototype.toString ( )
This method performs the following steps when called:
- Let func be the
this value. - If func
is an Object , func has a [[SourceText]] internal slot, func.[[SourceText]] is a sequence of Unicode code points, andHostHasSourceTextAvailable (func) istrue , then- Return
CodePointsToString (func.[[SourceText]]).
- Return
- If func is a
built-in function object , return animplementation-defined String source code representation of func. The representation must have the syntax of aNativeFunction . Additionally, if func has an [[InitialName]] internal slot and func.[[InitialName]]is a String , the portion of the returned String that would be matched byNativeFunctionAccessor opt PropertyName must be the value of func.[[InitialName]]. - If func
is an Object andIsCallable (func) istrue , return animplementation-defined String source code representation of func. The representation must have the syntax of aNativeFunction . - Throw a
TypeError exception.
20.2.3.6 Function.prototype [ %Symbol.hasInstance% ] ( V )
This method performs the following steps when called:
- Let F be the
this value. - Return ?
OrdinaryHasInstance (F, V).
This property has the attributes { [[Writable]]:
This is the default implementation of %Symbol.hasInstance% that most functions inherit. %Symbol.hasInstance% is called by the instanceof operator to determine whether a value is an instance of a specific
v instanceof Fevaluates as
F[%Symbol.hasInstance%](v)A instanceof by exposing a different %Symbol.hasInstance% method on the function.
This property is non-writable and non-configurable to prevent tampering that could be used to globally expose the target function of a bound function.
The value of the
20.2.4 Function Instances
Every Function instance is an ECMAScript Function.prototype.bind method (
Function instances have the following properties:
20.2.4.1 length
The value of the
20.2.4.2 name
The value of the
Anonymous functions objects that do not have a contextual name associated with them by this specification use the empty String as the value of the
20.2.4.3 prototype
Function instances that can be used as a
This property has the attributes { [[Writable]]:
Function.prototype.bind, or by evaluating a
20.2.5 HostHasSourceTextAvailable ( func )
The
An implementation of HostHasSourceTextAvailable must conform to the following requirements:
- It must be deterministic with respect to its parameters. Each time it is called with a specific func as its argument, it must return the same result.
The default implementation of HostHasSourceTextAvailable is to return
20.3 Boolean Objects
20.3.1 The Boolean Constructor
The Boolean
- is %Boolean%.
- is the initial value of the
"Boolean" property of theglobal object . - creates and initializes a new Boolean object when called as a
constructor . - performs a type conversion when called as a function rather than as a
constructor . - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Boolean behaviour must include asupercall to the Booleanconstructor to create and initialize the subclass instance with a [[BooleanData]] internal slot.
20.3.1.1 Boolean ( value )
This function performs the following steps when called:
- Let b be
ToBoolean (value). - If NewTarget is
undefined , return b. - Let O be ?
OrdinaryCreateFromConstructor (NewTarget,"%Boolean.prototype%" , « [[BooleanData]] »). - Set O.[[BooleanData]] to b.
- Return O.
20.3.2 Properties of the Boolean Constructor
The Boolean
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
20.3.2.1 Boolean.prototype
The initial value of Boolean.prototype is the
This property has the attributes { [[Writable]]:
20.3.3 Properties of the Boolean Prototype Object
The Boolean prototype object:
- is %Boolean.prototype%.
- is an
ordinary object . - is itself a Boolean object; it has a [[BooleanData]] internal slot with the value
false . - has a [[Prototype]] internal slot whose value is
%Object.prototype% .
20.3.3.1 Boolean.prototype.constructor
The initial value of Boolean.prototype.constructor is
20.3.3.2 Boolean.prototype.toString ( )
This method performs the following steps when called:
- Let b be ?
ThisBooleanValue (this value). - If b is
true , return"true" ; else return"false" .
20.3.3.3 Boolean.prototype.valueOf ( )
This method performs the following steps when called:
- Return ?
ThisBooleanValue (this value).
20.3.3.3.1 ThisBooleanValue ( value )
The abstract operation ThisBooleanValue takes argument value (an
- If value
is a Boolean , return value. - If value
is an Object and value has a [[BooleanData]] internal slot, then- Let b be value.[[BooleanData]].
Assert : bis a Boolean .- Return b.
- Throw a
TypeError exception.
20.3.4 Properties of Boolean Instances
Boolean instances are
20.4 Symbol Objects
20.4.1 The Symbol Constructor
The Symbol
- is %Symbol%.
- is the initial value of the
"Symbol" property of theglobal object . - returns a new Symbol value when called as a function.
- is not intended to be used with the
newoperator. - is not intended to be subclassed.
- may be used as the value of an
extendsclause of a class definition but asupercall to it will cause an exception.
20.4.1.1 Symbol ( [ description ] )
This function performs the following steps when called:
- If NewTarget is not
undefined , throw aTypeError exception. - If description is
undefined , let descString beundefined . - Else, let descString be ?
ToString (description). - Return a new Symbol whose [[Description]] is descString.
20.4.2 Properties of the Symbol Constructor
The Symbol
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
20.4.2.1 Symbol.asyncIterator
The initial value of Symbol.asyncIterator is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.2 Symbol.for ( key )
This function performs the following steps when called:
- Let stringKey be ?
ToString (key). - For each element e of the
GlobalSymbolRegistry List , do- If e.[[Key]] is stringKey, return e.[[Symbol]].
Assert : TheGlobalSymbolRegistry List does not currently contain an entry for stringKey.- Let newSymbol be a new Symbol whose [[Description]] is stringKey.
- Append the GlobalSymbolRegistry
Record { [[Key]]: stringKey, [[Symbol]]: newSymbol } to theGlobalSymbolRegistry List . - Return newSymbol.
The GlobalSymbolRegistry List is an append-only
20.4.2.3 Symbol.hasInstance
The initial value of Symbol.hasInstance is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.4 Symbol.isConcatSpreadable
The initial value of Symbol.isConcatSpreadable is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.5 Symbol.iterator
The initial value of Symbol.iterator is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.6 Symbol.keyFor ( sym )
This function performs the following steps when called:
- If sym
is not a Symbol , throw aTypeError exception. - Return
KeyForSymbol (sym).
20.4.2.7 Symbol.match
The initial value of Symbol.match is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.8 Symbol.matchAll
The initial value of Symbol.matchAll is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.9 Symbol.prototype
The initial value of Symbol.prototype is the
This property has the attributes { [[Writable]]:
20.4.2.10 Symbol.replace
The initial value of Symbol.replace is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.11 Symbol.search
The initial value of Symbol.search is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.12 Symbol.species
The initial value of Symbol.species is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.13 Symbol.split
The initial value of Symbol.split is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.14 Symbol.toPrimitive
The initial value of Symbol.toPrimitive is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.15 Symbol.toStringTag
The initial value of Symbol.toStringTag is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.2.16 Symbol.unscopables
The initial value of Symbol.unscopables is the well-known symbol
This property has the attributes { [[Writable]]:
20.4.3 Properties of the Symbol Prototype Object
The Symbol prototype object:
- is %Symbol.prototype%.
- is an
ordinary object . is not a Symbol instance and does not have a [[SymbolData]] internal slot.- has a [[Prototype]] internal slot whose value is
%Object.prototype% .
20.4.3.1 Symbol.prototype.constructor
The initial value of Symbol.prototype.constructor is
20.4.3.2 get Symbol.prototype.description
Symbol.prototype.description is an
- Let s be the
this value. - Let sym be ?
ThisSymbolValue (s). - Return sym.[[Description]].
20.4.3.3 Symbol.prototype.toString ( )
This method performs the following steps when called:
- Let sym be ?
ThisSymbolValue (this value). - Return
SymbolDescriptiveString (sym).
20.4.3.3.1 SymbolDescriptiveString ( sym )
The abstract operation SymbolDescriptiveString takes argument sym (a Symbol) and returns a String. It performs the following steps when called:
- Let desc be sym's [[Description]] value.
- If desc is
undefined , set desc to the empty String. Assert : descis a String .- Return the
string-concatenation of"Symbol(" , desc, and")" .
20.4.3.4 Symbol.prototype.valueOf ( )
This method performs the following steps when called:
- Return ?
ThisSymbolValue (this value).
20.4.3.4.1 ThisSymbolValue ( value )
The abstract operation ThisSymbolValue takes argument value (an
- If value
is a Symbol , return value. - If value
is an Object and value has a [[SymbolData]] internal slot, then- Let s be value.[[SymbolData]].
Assert : sis a Symbol .- Return s.
- Throw a
TypeError exception.
20.4.3.5 Symbol.prototype [ %Symbol.toPrimitive% ] ( hint )
This method is called by ECMAScript language operators to convert a Symbol object to a primitive value.
It performs the following steps when called:
- Return ?
ThisSymbolValue (this value).
The argument is ignored.
This property has the attributes { [[Writable]]:
The value of the
20.4.3.6 Symbol.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
20.4.4 Properties of Symbol Instances
Symbol instances are
20.4.5 Abstract Operations for Symbols
20.4.5.1 KeyForSymbol ( sym )
The abstract operation KeyForSymbol takes argument sym (a Symbol) and returns a String or
- For each element e of the
GlobalSymbolRegistry List , do- If
SameValue (e.[[Symbol]], sym) istrue , return e.[[Key]].
- If
Assert : TheGlobalSymbolRegistry List does not currently contain an entry for sym.- Return
undefined .
20.5 Error Objects
Instances of Error objects are thrown as exceptions when runtime errors occur. The Error objects may also serve as base objects for user-defined exception classes.
When an ECMAScript implementation detects a runtime error, it throws a new instance of one of the NativeError objects defined in
20.5.1 The Error Constructor
The Error
- is %Error%.
- is the initial value of the
"Error" property of theglobal object . - creates and initializes a new Error object when called as a function rather than as a
constructor . Thus the function callError(…)is equivalent to the object creation expressionnew Error(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Error behaviour must include asupercall to the Errorconstructor to create and initialize subclass instances with an [[ErrorData]] internal slot.
20.5.1.1 Error ( message [ , options ] )
This function performs the following steps when called:
- If NewTarget is
undefined , let newTarget be theactive function object ; else let newTarget be NewTarget. - Let O be ?
OrdinaryCreateFromConstructor (newTarget,"%Error.prototype%" , « [[ErrorData]] »). - If message is not
undefined , then- Let msg be ?
ToString (message). - Perform
CreateNonEnumerableDataPropertyOrThrow (O,"message" , msg).
- Let msg be ?
- Perform ?
InstallErrorCause (O, options). - Return O.
20.5.2 Properties of the Error Constructor
The Error
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
20.5.2.1 Error.prototype
The initial value of Error.prototype is the
This property has the attributes { [[Writable]]:
20.5.3 Properties of the Error Prototype Object
The Error prototype object:
- is %Error.prototype%.
- is an
ordinary object . - is not an Error instance and does not have an [[ErrorData]] internal slot.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% .
20.5.3.1 Error.prototype.constructor
The initial value of Error.prototype.constructor is
20.5.3.2 Error.prototype.message
The initial value of Error.prototype.message is the empty String.
20.5.3.3 Error.prototype.name
The initial value of Error.prototype.name is
20.5.3.4 Error.prototype.toString ( )
This method performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - Let name be ?
Get (O,"name" ). - If name is
undefined , set name to"Error" ; otherwise set name to ?ToString (name). - Let msg be ?
Get (O,"message" ). - If msg is
undefined , set msg to the empty String; otherwise set msg to ?ToString (msg). - If name is the empty String, return msg.
- If msg is the empty String, return name.
- Return the
string-concatenation of name, the code unit 0x003A (COLON), the code unit 0x0020 (SPACE), and msg.
20.5.4 Properties of Error Instances
Error instances are Object.prototype.toString.
20.5.5 Native Error Types Used in This Standard
A new instance of one of the NativeError objects below or of the AggregateError object is thrown when a runtime error is detected. All NativeError objects share the same structure, as described in
20.5.5.1 EvalError
The EvalError
This exception is not currently used within this specification. This object remains for compatibility with previous editions of this specification.
20.5.5.2 RangeError
The RangeError
Indicates a value that is not in the set or range of allowable values.
20.5.5.3 ReferenceError
The ReferenceError
Indicate that an invalid reference has been detected.
20.5.5.4 SyntaxError
The SyntaxError
Indicates that a parsing error has occurred.
20.5.5.5 TypeError
The TypeError
TypeError is used to indicate an unsuccessful operation when none of the other NativeError objects are an appropriate indication of the failure cause.
20.5.5.6 URIError
The URIError
Indicates that one of the global URI handling functions was used in a way that is incompatible with its definition.
20.5.6 NativeError Object Structure
Each of these objects has the structure described below, differing only in the name used as the
For each error object, references to NativeError in the definition should be replaced with the appropriate error object name from
20.5.6.1 The NativeError Constructors
Each NativeError
- creates and initializes a new NativeError object when called as a function rather than as a
constructor . A call of the object as a function is equivalent to calling it as aconstructor with the same arguments. Thus the function callNativeError(…)is equivalent to the object creation expressionnew NativeError(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified NativeError behaviour must include asupercall to the NativeErrorconstructor to create and initialize subclass instances with an [[ErrorData]] internal slot.
20.5.6.1.1 NativeError ( message [ , options ] )
Each NativeError function performs the following steps when called:
- If NewTarget is
undefined , let newTarget be theactive function object ; else let newTarget be NewTarget. - Let O be ?
OrdinaryCreateFromConstructor (newTarget,"%NativeError.prototype%", « [[ErrorData]] »). - If message is not
undefined , then- Let msg be ?
ToString (message). - Perform
CreateNonEnumerableDataPropertyOrThrow (O,"message" , msg).
- Let msg be ?
- Perform ?
InstallErrorCause (O, options). - Return O.
The actual value of the string passed in step
20.5.6.2 Properties of the NativeError Constructors
Each NativeError
- has a [[Prototype]] internal slot whose value is
%Error% . - has a
"name" property whose value is the String value"NativeError" . - has the following properties:
20.5.6.2.1 NativeError.prototype
The initial value of NativeError.prototype is a NativeError prototype object (
This property has the attributes { [[Writable]]:
20.5.6.3 Properties of the NativeError Prototype Objects
Each NativeError prototype object:
- is an
ordinary object . - is not an Error instance and does not have an [[ErrorData]] internal slot.
- has a [[Prototype]] internal slot whose value is
%Error.prototype% .
20.5.6.3.1 NativeError.prototype.constructor
The initial value of the
20.5.6.3.2 NativeError.prototype.message
The initial value of the
20.5.6.3.3 NativeError.prototype.name
The initial value of the
20.5.6.4 Properties of NativeError Instances
NativeError instances are Object.prototype.toString (
20.5.7 AggregateError Objects
20.5.7.1 The AggregateError Constructor
The AggregateError
- is %AggregateError%.
- is the initial value of the
"AggregateError" property of theglobal object . - creates and initializes a new AggregateError object when called as a function rather than as a
constructor . Thus the function callAggregateError(…)is equivalent to the object creation expressionnew AggregateError(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified AggregateError behaviour must include asupercall to the AggregateErrorconstructor to create and initialize subclass instances with an [[ErrorData]] internal slot.
20.5.7.1.1 AggregateError ( errors, message [ , options ] )
This function performs the following steps when called:
- If NewTarget is
undefined , let newTarget be theactive function object ; else let newTarget be NewTarget. - Let O be ?
OrdinaryCreateFromConstructor (newTarget,"%AggregateError.prototype%" , « [[ErrorData]] »). - If message is not
undefined , then- Let msg be ?
ToString (message). - Perform
CreateNonEnumerableDataPropertyOrThrow (O,"message" , msg).
- Let msg be ?
- Perform ?
InstallErrorCause (O, options). - Let errorsList be ?
IteratorToList (?GetIterator (errors,sync )). - Perform !
DefinePropertyOrThrow (O,"errors" , PropertyDescriptor { [[Configurable]]:true , [[Enumerable]]:false , [[Writable]]:true , [[Value]]:CreateArrayFromList (errorsList) }). - Return O.
20.5.7.2 Properties of the AggregateError Constructor
The AggregateError
- has a [[Prototype]] internal slot whose value is
%Error% . - has the following properties:
20.5.7.2.1 AggregateError.prototype
The initial value of AggregateError.prototype is
This property has the attributes { [[Writable]]:
20.5.7.3 Properties of the AggregateError Prototype Object
The AggregateError prototype object:
- is %AggregateError.prototype%.
- is an
ordinary object . - is not an Error instance or an AggregateError instance and does not have an [[ErrorData]] internal slot.
- has a [[Prototype]] internal slot whose value is
%Error.prototype% .
20.5.7.3.1 AggregateError.prototype.constructor
The initial value of AggregateError.prototype.constructor is
20.5.7.3.2 AggregateError.prototype.message
The initial value of AggregateError.prototype.message is the empty String.
20.5.7.3.3 AggregateError.prototype.name
The initial value of AggregateError.prototype.name is
20.5.7.4 Properties of AggregateError Instances
AggregateError instances are Object.prototype.toString (
20.5.8 Abstract Operations for Error Objects
20.5.8.1 InstallErrorCause ( O, options )
The abstract operation InstallErrorCause takes arguments O (an Object) and options (an
- If options
is an Object and ?HasProperty (options,"cause" ) istrue , then- Let cause be ?
Get (options,"cause" ). - Perform
CreateNonEnumerableDataPropertyOrThrow (O,"cause" , cause).
- Let cause be ?
- Return
unused .
21 Numbers and Dates
21.1 Number Objects
21.1.1 The Number Constructor
The Number
- is %Number%.
- is the initial value of the
"Number" property of theglobal object . - creates and initializes a new Number object when called as a
constructor . - performs a type conversion when called as a function rather than as a
constructor . - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Number behaviour must include asupercall to the Numberconstructor to create and initialize the subclass instance with a [[NumberData]] internal slot.
21.1.1.1 Number ( value )
This function performs the following steps when called:
- If value is present, then
- Let prim be ?
ToNumeric (value). - If prim
is a BigInt , let n be𝔽 (ℝ (prim)). - Otherwise, let n be prim.
- Let prim be ?
- Else,
- Let n be
+0 𝔽.
- Let n be
- If NewTarget is
undefined , return n. - Let O be ?
OrdinaryCreateFromConstructor (NewTarget,"%Number.prototype%" , « [[NumberData]] »). - Set O.[[NumberData]] to n.
- Return O.
21.1.2 Properties of the Number Constructor
The Number
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
21.1.2.1 Number.EPSILON
The value of Number.EPSILON is the
This property has the attributes { [[Writable]]:
21.1.2.2 Number.isFinite ( number )
This function performs the following steps when called:
- If number
is not a Number , returnfalse . - If number is not
finite , returnfalse . - Otherwise, return
true .
21.1.2.3 Number.isInteger ( number )
This function performs the following steps when called:
- If number is an
integral Number , returntrue . - Return
false .
21.1.2.4 Number.isNaN ( number )
This function performs the following steps when called:
- If number
is not a Number , returnfalse . - If number is
NaN , returntrue . - Otherwise, return
false .
This function differs from the global isNaN function (
21.1.2.5 Number.isSafeInteger ( number )
An
This function performs the following steps when called:
- If number is an
integral Number , then - Return
false .
21.1.2.6 Number.MAX_SAFE_INTEGER
Due to rounding behaviour necessitated by precision limitations of Number.MAX_SAFE_INTEGER is shared with at least one other 9007199254740992 and 9007199254740993 evaluate to the Number value
The value of Number.MAX_SAFE_INTEGER is
This property has the attributes { [[Writable]]:
21.1.2.7 Number.MAX_VALUE
The value of Number.MAX_VALUE is the largest positive
This property has the attributes { [[Writable]]:
21.1.2.8 Number.MIN_SAFE_INTEGER
Due to rounding behaviour necessitated by precision limitations of Number.MIN_SAFE_INTEGER is shared with at least one other -9007199254740992 and -9007199254740993 evaluate to the Number value
The value of Number.MIN_SAFE_INTEGER is
This property has the attributes { [[Writable]]:
21.1.2.9 Number.MIN_VALUE
The value of Number.MIN_VALUE is the smallest positive value of the
In the Number.MIN_VALUE must be the smallest non-zero positive value that can actually be represented by the implementation.
This property has the attributes { [[Writable]]:
21.1.2.10 Number.NaN
The value of Number.NaN is
This property has the attributes { [[Writable]]:
21.1.2.11 Number.NEGATIVE_INFINITY
The value of Number.NEGATIVE_INFINITY is
This property has the attributes { [[Writable]]:
21.1.2.12 Number.parseFloat ( string )
The initial value of the
21.1.2.13 Number.parseInt ( string, radix )
The initial value of the
21.1.2.14 Number.POSITIVE_INFINITY
The value of Number.POSITIVE_INFINITY is
This property has the attributes { [[Writable]]:
21.1.2.15 Number.prototype
The initial value of Number.prototype is the
This property has the attributes { [[Writable]]:
21.1.3 Properties of the Number Prototype Object
The Number prototype object:
- is %Number.prototype%.
- is an
ordinary object . - is itself a Number object; it has a [[NumberData]] internal slot with the value
+0 𝔽. - has a [[Prototype]] internal slot whose value is
%Object.prototype% .
Unless explicitly stated otherwise, the methods of the Number prototype object defined below are not generic and the
The phrase “this Number value” within the specification of a method refers to the result returned by calling the abstract operation
21.1.3.1 Number.prototype.constructor
The initial value of Number.prototype.constructor is
21.1.3.2 Number.prototype.toExponential ( fractionDigits )
This method returns a String containing this Number value represented in decimal exponential notation with one digit before the significand's decimal point and fractionDigits digits after the significand's decimal point. If fractionDigits is
It performs the following steps when called:
- Let x be ?
ThisNumberValue (this value). - Let f be ?
ToIntegerOrInfinity (fractionDigits). Assert : If fractionDigits isundefined , then f is 0.- If x is not
finite , returnNumber::toString (x, 10). - If f < 0 or f > 100, throw a
RangeError exception. - Set x to
ℝ (x). - Let s be the empty String.
- If x < 0, then
- Set s to
"-" . - Set x to -x.
- Set s to
- If x = 0, then
- Let m be the String value consisting of f + 1 occurrences of the code unit 0x0030 (DIGIT ZERO).
- Let e be 0.
- Else,
- If fractionDigits is not
undefined , then- Let e and n be
integers such that 10f ≤ n < 10f + 1 and for which n × 10e - f - x is as close to zero as possible. If there are two such sets of e and n, pick the e and n for which n × 10e - f is larger.
- Let e and n be
- Else,
- Let e, n, and ff be
integers such that ff ≥ 0, 10ff ≤ n < 10ff + 1,𝔽 (n × 10e - ff) is𝔽 (x), and ff is as small as possible. Note that the decimal representation of n has ff + 1 digits, n is not divisible by 10, and the least significant digit of n is not necessarily uniquely determined by these criteria. - Set f to ff.
- Let e, n, and ff be
- Let m be the String value consisting of the digits of the decimal representation of n (in order, with no leading zeroes).
- If fractionDigits is not
- If f ≠ 0, then
- Let a be the first code unit of m.
- Let b be the other f code units of m.
- Set m to the
string-concatenation of a,"." , and b.
- If e = 0, then
- Let c be
"+" . - Let d be
"0" .
- Let c be
- Else,
- If e > 0, then
- Let c be
"+" .
- Let c be
- Else,
Assert : e < 0.- Let c be
"-" . - Set e to -e.
- Let d be the String value consisting of the digits of the decimal representation of e (in order, with no leading zeroes).
- If e > 0, then
- Set m to the
string-concatenation of m,"e" , c, and d. - Return the
string-concatenation of s and m.
For implementations that provide more accurate conversions than required by the rules above, it is recommended that the following alternative version of step
- Let e, n, and f be
integers such that f ≥ 0, 10f ≤ n < 10f + 1,𝔽 (n × 10e - f) is𝔽 (x), and f is as small as possible. If there are multiple possibilities for n, choose the value of n for which𝔽 (n × 10e - f) is closest in value to𝔽 (x). If there are two such possible values of n, choose the one that is even.
21.1.3.3 Number.prototype.toFixed ( fractionDigits )
This method returns a String containing this Number value represented in decimal fixed-point notation with fractionDigits digits after the decimal point. If fractionDigits is
It performs the following steps when called:
- Let x be ?
ThisNumberValue (this value). - Let f be ?
ToIntegerOrInfinity (fractionDigits). Assert : If fractionDigits isundefined , then f is 0.- If f is not
finite , throw aRangeError exception. - If f < 0 or f > 100, throw a
RangeError exception. - If x is not
finite , returnNumber::toString (x, 10). - Set x to
ℝ (x). - Let s be the empty String.
- If x < 0, then
- Set s to
"-" . - Set x to -x.
- Set s to
- If x ≥ 1021, then
- Else,
- Let n be an
integer for which n / 10f - x is as close to zero as possible. If there are two such n, pick the larger n. - If n = 0, let m be
"0" . Otherwise, let m be the String value consisting of the digits of the decimal representation of n (in order, with no leading zeroes). - If f ≠ 0, then
- Let k be the length of m.
- If k ≤ f, then
- Let z be the String value consisting of f + 1 - k occurrences of the code unit 0x0030 (DIGIT ZERO).
- Set m to the
string-concatenation of z and m. - Set k to f + 1.
- Let a be the first k - f code units of m.
- Let b be the other f code units of m.
- Set m to the
string-concatenation of a,"." , and b.
- Let n be an
- Return the
string-concatenation of s and m.
The output of toFixed may be more precise than toString for some values because toString only prints enough significant digits to distinguish the number from adjacent Number values. For example,
(1000000000000000128).toString() returns
(1000000000000000128).toFixed(0) returns
21.1.3.4 Number.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method produces a String value that represents this Number value formatted according to the conventions of the toString.
The meanings of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.1.3.5 Number.prototype.toPrecision ( precision )
This method returns a String containing this Number value represented either in decimal exponential notation with one digit before the significand's decimal point and
It performs the following steps when called:
- Let x be ?
ThisNumberValue (this value). - If precision is
undefined , return !ToString (x). - Let p be ?
ToIntegerOrInfinity (precision). - If x is not
finite , returnNumber::toString (x, 10). - If p < 1 or p > 100, throw a
RangeError exception. - Set x to
ℝ (x). - Let s be the empty String.
- If x < 0, then
- Set s to the code unit 0x002D (HYPHEN-MINUS).
- Set x to -x.
- If x = 0, then
- Let m be the String value consisting of p occurrences of the code unit 0x0030 (DIGIT ZERO).
- Let e be 0.
- Else,
- Let e and n be
integers such that 10p - 1 ≤ n < 10p and for which n × 10e - p + 1 - x is as close to zero as possible. If there are two such sets of e and n, pick the e and n for which n × 10e - p + 1 is larger. - Let m be the String value consisting of the digits of the decimal representation of n (in order, with no leading zeroes).
- If e < -6 or e ≥ p, then
Assert : e ≠ 0.- If p ≠ 1, then
- Let a be the first code unit of m.
- Let b be the other p - 1 code units of m.
- Set m to the
string-concatenation of a,"." , and b.
- If e > 0, then
- Let c be the code unit 0x002B (PLUS SIGN).
- Else,
Assert : e < 0.- Let c be the code unit 0x002D (HYPHEN-MINUS).
- Set e to -e.
- Let d be the String value consisting of the digits of the decimal representation of e (in order, with no leading zeroes).
- Return the
string-concatenation of s, m, the code unit 0x0065 (LATIN SMALL LETTER E), c, and d.
- Let e and n be
- If e = p - 1, return the
string-concatenation of s and m. - If e ≥ 0, then
- Set m to the
string-concatenation of the first e + 1 code units of m, the code unit 0x002E (FULL STOP), and the remaining p - (e + 1) code units of m.
- Set m to the
- Else,
- Set m to the
string-concatenation of the code unit 0x0030 (DIGIT ZERO), the code unit 0x002E (FULL STOP), -(e + 1) occurrences of the code unit 0x0030 (DIGIT ZERO), and the String m.
- Set m to the
- Return the
string-concatenation of s and m.
21.1.3.6 Number.prototype.toString ( [ radix ] )
The optional radix should be an
This method performs the following steps when called:
- Let x be ?
ThisNumberValue (this value). - If radix is
undefined , let radixMV be 10. - Else, let radixMV be ?
ToIntegerOrInfinity (radix). - If radixMV is not in the
inclusive interval from 2 to 36, throw aRangeError exception. - Return
Number::toString (x, radixMV).
This method is not generic; it throws a
The
21.1.3.7 Number.prototype.valueOf ( )
- Return ?
ThisNumberValue (this value).
21.1.3.7.1 ThisNumberValue ( value )
The abstract operation ThisNumberValue takes argument value (an
- If value
is a Number , return value. - If value
is an Object and value has a [[NumberData]] internal slot, then- Let n be value.[[NumberData]].
Assert : nis a Number .- Return n.
- Throw a
TypeError exception.
21.1.4 Properties of Number Instances
Number instances are
21.2 BigInt Objects
21.2.1 The BigInt Constructor
The BigInt
- is %BigInt%.
- is the initial value of the
"BigInt" property of theglobal object . - performs a type conversion when called as a function rather than as a
constructor . - is not intended to be used with the
newoperator or to be subclassed. It may be used as the value of anextendsclause of a class definition but asupercall to the BigIntconstructor will cause an exception.
21.2.1.1 BigInt ( value )
This function performs the following steps when called:
- If NewTarget is not
undefined , throw aTypeError exception. - Let prim be ?
ToPrimitive (value,number ). - If prim
is a Number , return ?NumberToBigInt (prim). - Otherwise, return ?
ToBigInt (prim).
21.2.1.1.1 NumberToBigInt ( number )
The abstract operation NumberToBigInt takes argument number (a Number) and returns either a
- If number is not an
integral Number , throw aRangeError exception. - Return
ℤ (ℝ (number)).
21.2.2 Properties of the BigInt Constructor
The BigInt
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
21.2.2.1 BigInt.asIntN ( bits, bigint )
This function performs the following steps when called:
21.2.2.2 BigInt.asUintN ( bits, bigint )
This function performs the following steps when called:
21.2.2.3 BigInt.prototype
The initial value of BigInt.prototype is the
This property has the attributes { [[Writable]]:
21.2.3 Properties of the BigInt Prototype Object
The BigInt prototype object:
- is %BigInt.prototype%.
- is an
ordinary object . is not a BigInt object; it does not have a [[BigIntData]] internal slot.- has a [[Prototype]] internal slot whose value is
%Object.prototype% .
The phrase “this BigInt value” within the specification of a method refers to the result returned by calling the abstract operation
21.2.3.1 BigInt.prototype.constructor
The initial value of BigInt.prototype.constructor is
21.2.3.2 BigInt.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method produces a String value that represents this BigInt value formatted according to the conventions of the toString.
The meanings of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.2.3.3 BigInt.prototype.toString ( [ radix ] )
The optional radix should be an
This method performs the following steps when called:
- Let x be ?
ThisBigIntValue (this value). - If radix is
undefined , let radixMV be 10. - Else, let radixMV be ?
ToIntegerOrInfinity (radix). - If radixMV is not in the
inclusive interval from 2 to 36, throw aRangeError exception. - Return
BigInt::toString (x, radixMV).
This method is not generic; it throws a
21.2.3.4 BigInt.prototype.valueOf ( )
- Return ?
ThisBigIntValue (this value).
21.2.3.4.1 ThisBigIntValue ( value )
The abstract operation ThisBigIntValue takes argument value (an
- If value
is a BigInt , return value. - If value
is an Object and value has a [[BigIntData]] internal slot, thenAssert : value.[[BigIntData]]is a BigInt .- Return value.[[BigIntData]].
- Throw a
TypeError exception.
21.2.3.5 BigInt.prototype [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
21.2.4 Properties of BigInt Instances
BigInt instances are
21.3 The Math Object
The Math object:
- is %Math%.
- is the initial value of the
"Math" property of theglobal object . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Object.prototype% . - is not a
function object . - does not have a [[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a [[Call]] internal method; it cannot be invoked as a function.
In this specification, the phrase “the
21.3.1 Value Properties of the Math Object
21.3.1.1 Math.E
The
This property has the attributes { [[Writable]]:
21.3.1.2 Math.LN10
The
This property has the attributes { [[Writable]]:
21.3.1.3 Math.LN2
The
This property has the attributes { [[Writable]]:
21.3.1.4 Math.LOG10E
The
This property has the attributes { [[Writable]]:
The value of Math.LOG10E is approximately the reciprocal of the value of Math.LN10.
21.3.1.5 Math.LOG2E
The
This property has the attributes { [[Writable]]:
The value of Math.LOG2E is approximately the reciprocal of the value of Math.LN2.
21.3.1.6 Math.PI
The
This property has the attributes { [[Writable]]:
21.3.1.7 Math.SQRT1_2
The
This property has the attributes { [[Writable]]:
The value of Math.SQRT1_2 is approximately the reciprocal of the value of Math.SQRT2.
21.3.1.8 Math.SQRT2
The
This property has the attributes { [[Writable]]:
21.3.1.9 Math [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
21.3.2 Function Properties of the Math Object
The behaviour of the functions acos, acosh, asin, asinh, atan, atanh, atan2, cbrt, cos, cosh, exp, expm1, hypot, log, log1p, log2, log10, pow, random, sin, sinh, tan, and tanh is not precisely specified here except to require specific results for certain argument values that represent boundary cases of interest. For other argument values, these functions are intended to compute approximations to the results of familiar mathematical functions, but some latitude is allowed in the choice of approximation algorithms. The general intent is that an implementer should be able to use the same mathematical library for ECMAScript on a given hardware platform that is available to C programmers on that platform.
Although the choice of algorithms is left to the implementation, it is recommended (but not specified by this standard) that implementations use the approximation algorithms for fdlibm, the freely distributable mathematical library from Sun Microsystems (http://www.netlib.org/fdlibm).
21.3.2.1 Math.abs ( x )
This function returns the absolute value of x; the result has the same magnitude as x but has positive sign.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is
NaN , returnNaN . - If n is
-0 𝔽, return+0 𝔽. - If n is
-∞ 𝔽, return+∞ 𝔽. - If n <
-0 𝔽, return -n. - Return n.
21.3.2.2 Math.acos ( x )
This function returns the inverse cosine of x. The result is expressed in radians and is in the
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is
NaN , n >1 𝔽, or n <-1 𝔽, returnNaN . - If n is
1 𝔽, return+0 𝔽. - Return an
implementation-approximated Number value representing the inverse cosine ofℝ (n).
21.3.2.3 Math.acosh ( x )
This function returns the inverse hyperbolic cosine of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is either
NaN or+∞ 𝔽, return n. - If n is
1 𝔽, return+0 𝔽. - If n <
1 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the inverse hyperbolic cosine ofℝ (n).
21.3.2.4 Math.asin ( x )
This function returns the inverse sine of x. The result is expressed in radians and is in the
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n >
1 𝔽 or n <-1 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the inverse sine ofℝ (n).
21.3.2.5 Math.asinh ( x )
This function returns the inverse hyperbolic sine of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - Return an
implementation-approximated Number value representing the inverse hyperbolic sine ofℝ (n).
21.3.2.6 Math.atan ( x )
This function returns the inverse tangent of x. The result is expressed in radians and is in the
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n is
+∞ 𝔽, return animplementation-approximated Number value representing π / 2. - If n is
-∞ 𝔽, return animplementation-approximated Number value representing -π / 2. - Return an
implementation-approximated Number value representing the inverse tangent ofℝ (n).
21.3.2.7 Math.atanh ( x )
This function returns the inverse hyperbolic tangent of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n >
1 𝔽 or n <-1 𝔽, returnNaN . - If n is
1 𝔽, return+∞ 𝔽. - If n is
-1 𝔽, return-∞ 𝔽. - Return an
implementation-approximated Number value representing the inverse hyperbolic tangent ofℝ (n).
21.3.2.8 Math.atan2 ( y, x )
This function returns the inverse tangent of the quotient
It performs the following steps when called:
- Let ny be ?
ToNumber (y). - Let nx be ?
ToNumber (x). - If ny is
NaN or nx isNaN , returnNaN . - If ny is
+∞ 𝔽, then- If nx is
+∞ 𝔽, return animplementation-approximated Number value representing π / 4. - If nx is
-∞ 𝔽, return animplementation-approximated Number value representing 3π / 4. - Return an
implementation-approximated Number value representing π / 2.
- If nx is
- If ny is
-∞ 𝔽, then- If nx is
+∞ 𝔽, return animplementation-approximated Number value representing -π / 4. - If nx is
-∞ 𝔽, return animplementation-approximated Number value representing -3π / 4. - Return an
implementation-approximated Number value representing -π / 2.
- If nx is
- If ny is
+0 𝔽, then- If nx >
+0 𝔽 or nx is+0 𝔽, return+0 𝔽. - Return an
implementation-approximated Number value representing π.
- If nx >
- If ny is
-0 𝔽, then- If nx >
+0 𝔽 or nx is+0 𝔽, return-0 𝔽. - Return an
implementation-approximated Number value representing -π.
- If nx >
Assert : ny isfinite and is neither+0 𝔽 nor-0 𝔽.- If ny >
+0 𝔽, then- If nx is
+∞ 𝔽, return+0 𝔽. - If nx is
-∞ 𝔽, return animplementation-approximated Number value representing π. - If nx is either
+0 𝔽 or-0 𝔽, return animplementation-approximated Number value representing π / 2.
- If nx is
- If ny <
-0 𝔽, then- If nx is
+∞ 𝔽, return-0 𝔽. - If nx is
-∞ 𝔽, return animplementation-approximated Number value representing -π. - If nx is either
+0 𝔽 or-0 𝔽, return animplementation-approximated Number value representing -π / 2.
- If nx is
Assert : nx isfinite and is neither+0 𝔽 nor-0 𝔽.- Let r be the inverse tangent of
abs (ℝ (ny) /ℝ (nx)). - If nx <
-0 𝔽, then- If ny >
+0 𝔽, set r to π - r. - Else, set r to -π + r.
- If ny >
- Else,
- If ny <
-0 𝔽, set r to -r.
- If ny <
- Return an
implementation-approximated Number value representing r.
21.3.2.9 Math.cbrt ( x )
This function returns the cube root of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - Return an
implementation-approximated Number value representing the cube root ofℝ (n).
21.3.2.10 Math.ceil ( x )
This function returns the smallest (closest to -∞)
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - If n <
-0 𝔽 and n >-1 𝔽, return-0 𝔽. - If n is an
integral Number , return n. - Return the smallest (closest to -∞)
integral Number value that is not less than n.
The value of Math.ceil(x) is the same as the value of -Math.floor(-x).
21.3.2.11 Math.clz32 ( x )
This function performs the following steps when called:
If n is either
21.3.2.12 Math.cos ( x )
This function returns the cosine of x. The argument is expressed in radians.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite , returnNaN . - If n is either
+0 𝔽 or-0 𝔽, return1 𝔽. - Return an
implementation-approximated Number value representing the cosine ofℝ (n).
21.3.2.13 Math.cosh ( x )
This function returns the hyperbolic cosine of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is
NaN , returnNaN . - If n is either
+∞ 𝔽 or-∞ 𝔽, return+∞ 𝔽. - If n is either
+0 𝔽 or-0 𝔽, return1 𝔽. - Return an
implementation-approximated Number value representing the hyperbolic cosine ofℝ (n).
The value of Math.cosh(x) is the same as the value of (Math.exp(x) + Math.exp(-x)) / 2.
21.3.2.14 Math.exp ( x )
This function returns the exponential function of x (e raised to the power of x, where e is the base of the natural logarithms).
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is either
NaN or+∞ 𝔽, return n. - If n is either
+0 𝔽 or-0 𝔽, return1 𝔽. - If n is
-∞ 𝔽, return+0 𝔽. - Return an
implementation-approximated Number value representing the exponential function ofℝ (n).
21.3.2.15 Math.expm1 ( x )
This function returns the result of subtracting 1 from the exponential function of x (e raised to the power of x, where e is the base of the natural logarithms). The result is computed in a way that is accurate even when the value of x is close to 0.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽,-0 𝔽, or+∞ 𝔽, return n. - If n is
-∞ 𝔽, return-1 𝔽. - Let exp be the exponential function of
ℝ (n). - Return an
implementation-approximated Number value representing exp - 1.
21.3.2.16 Math.floor ( x )
This function returns the greatest (closest to +∞)
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - If n <
1 𝔽 and n >+0 𝔽, return+0 𝔽. - If n is an
integral Number , return n. - Return the greatest (closest to +∞)
integral Number value that is not greater than n.
The value of Math.floor(x) is the same as the value of -Math.ceil(-x).
21.3.2.17 Math.fround ( x )
This function performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is
NaN , returnNaN . - If n is one of
+0 𝔽,-0 𝔽,+∞ 𝔽, or-∞ 𝔽, return n. - Let n32 be the result of converting n to
IEEE 754-2019 binary32 format using roundTiesToEven mode. - Let n64 be the result of converting n32 to
IEEE 754-2019 binary64 format. - Return the ECMAScript Number value corresponding to n64.
21.3.2.18 Math.f16round ( x )
This function performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is
NaN , returnNaN . - If n is one of
+0 𝔽,-0 𝔽,+∞ 𝔽, or-∞ 𝔽, return n. - Let n16 be the result of converting n to
IEEE 754-2019 binary16 format using roundTiesToEven mode. - Let n64 be the result of converting n16 to
IEEE 754-2019 binary64 format. - Return the ECMAScript Number value corresponding to n64.
This operation is not the same as casting to binary32 and then to binary16 because of the possibility of double-rounding: consider the number k =
Not all platforms provide native support for casting from binary64 to binary16. There are various libraries which can provide this, including the MIT-licensed half library. Alternatively, it is possible to first cast from binary64 to binary32 under roundTiesToEven and then check whether the result could lead to incorrect double-rounding. The cases which could can be handled explicitly by adjusting the mantissa of the binary32 value so that it is the value which would be produced by performing the initial cast under roundTiesToOdd. Casting the adjusted value to binary16 under roundTiesToEven then produces the correct value.
21.3.2.19 Math.hypot ( ...args )
Given zero or more arguments, this function returns the square root of the sum of squares of its arguments.
It performs the following steps when called:
- Let coerced be a new empty
List . - For each element arg of args, do
- Let n be ?
ToNumber (arg). - Append n to coerced.
- Let n be ?
- For each element number of coerced, do
- If number is either
+∞ 𝔽 or-∞ 𝔽, return+∞ 𝔽.
- If number is either
- Let onlyZero be
true . - For each element number of coerced, do
- If number is
NaN , returnNaN . - If number is neither
+0 𝔽 nor-0 𝔽, set onlyZero tofalse .
- If number is
- If onlyZero is
true , return+0 𝔽. - Return an
implementation-approximated Number value representing the square root of the sum of squares of themathematical values of the elements of coerced.
The
Implementations should take care to avoid the loss of precision from overflows and underflows that are prone to occur in naive implementations when this function is called with two or more arguments.
21.3.2.20 Math.imul ( x, y )
This function performs the following steps when called:
21.3.2.21 Math.log ( x )
This function returns the natural logarithm of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is either
NaN or+∞ 𝔽, return n. - If n is
1 𝔽, return+0 𝔽. - If n is either
+0 𝔽 or-0 𝔽, return-∞ 𝔽. - If n <
-0 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the natural logarithm ofℝ (n).
21.3.2.22 Math.log1p ( x )
This function returns the natural logarithm of 1 + x. The result is computed in a way that is accurate even when the value of x is close to zero.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽,-0 𝔽, or+∞ 𝔽, return n. - If n is
-1 𝔽, return-∞ 𝔽. - If n <
-1 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the natural logarithm of 1 +ℝ (n).
21.3.2.23 Math.log10 ( x )
This function returns the base 10 logarithm of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is either
NaN or+∞ 𝔽, return n. - If n is
1 𝔽, return+0 𝔽. - If n is either
+0 𝔽 or-0 𝔽, return-∞ 𝔽. - If n <
-0 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the base 10 logarithm ofℝ (n).
21.3.2.24 Math.log2 ( x )
This function returns the base 2 logarithm of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is either
NaN or+∞ 𝔽, return n. - If n is
1 𝔽, return+0 𝔽. - If n is either
+0 𝔽 or-0 𝔽, return-∞ 𝔽. - If n <
-0 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the base 2 logarithm ofℝ (n).
21.3.2.25 Math.max ( ...args )
Given zero or more arguments, this function calls
It performs the following steps when called:
- Let coerced be a new empty
List . - For each element arg of args, do
- Let n be ?
ToNumber (arg). - Append n to coerced.
- Let n be ?
- Let highest be
-∞ 𝔽. - For each element number of coerced, do
- If number is
NaN , returnNaN . - If number is
+0 𝔽 and highest is-0 𝔽, set highest to+0 𝔽. - If number > highest, set highest to number.
- If number is
- Return highest.
The comparison of values to determine the largest value is done using the
The
21.3.2.26 Math.min ( ...args )
Given zero or more arguments, this function calls
It performs the following steps when called:
- Let coerced be a new empty
List . - For each element arg of args, do
- Let n be ?
ToNumber (arg). - Append n to coerced.
- Let n be ?
- Let lowest be
+∞ 𝔽. - For each element number of coerced, do
- If number is
NaN , returnNaN . - If number is
-0 𝔽 and lowest is+0 𝔽, set lowest to-0 𝔽. - If number < lowest, set lowest to number.
- If number is
- Return lowest.
The comparison of values to determine the largest value is done using the
The
21.3.2.27 Math.pow ( base, exponent )
This function performs the following steps when called:
- Set base to ?
ToNumber (base). - Set exponent to ?
ToNumber (exponent). - Return
Number::exponentiate (base, exponent).
21.3.2.28 Math.random ( )
This function returns a Number value with positive sign, greater than or equal to
Each Math.random function created for distinct
21.3.2.29 Math.round ( x )
This function returns the Number value that is closest to x and is integral. If two
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is anintegral Number , return n. - If n <
0.5 𝔽 and n >+0 𝔽, return+0 𝔽. - If n <
-0 𝔽 and n ≥-0.5 𝔽, return-0 𝔽. - Return the
integral Number closest to n, preferring the Number closer to +∞ in the case of a tie.
Math.round(3.5) returns 4, but Math.round(-3.5) returns -3.
The value of Math.round(x) is not always the same as the value of Math.floor(x + 0.5). When x is x is less than Math.round(x) returns Math.floor(x + 0.5) returns Math.round(x) may also differ from the value of Math.floor(x + 0.5)because of internal rounding when computing x + 0.5.
21.3.2.30 Math.sign ( x )
This function returns the sign of x, indicating whether x is positive, negative, or zero.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n <
-0 𝔽, return-1 𝔽. - Return
1 𝔽.
21.3.2.31 Math.sin ( x )
This function returns the sine of x. The argument is expressed in radians.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n is either
+∞ 𝔽 or-∞ 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the sine ofℝ (n).
21.3.2.32 Math.sinh ( x )
This function returns the hyperbolic sine of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - Return an
implementation-approximated Number value representing the hyperbolic sine ofℝ (n).
The value of Math.sinh(x) is the same as the value of (Math.exp(x) - Math.exp(-x)) / 2.
21.3.2.33 Math.sqrt ( x )
This function returns the square root of x.
It performs the following steps when called:
21.3.2.34 Math.tan ( x )
This function returns the tangent of x. The argument is expressed in radians.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n is either
+∞ 𝔽 or-∞ 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the tangent ofℝ (n).
21.3.2.35 Math.tanh ( x )
This function returns the hyperbolic tangent of x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is one of
NaN ,+0 𝔽, or-0 𝔽, return n. - If n is
+∞ 𝔽, return1 𝔽. - If n is
-∞ 𝔽, return-1 𝔽. - Return an
implementation-approximated Number value representing the hyperbolic tangent ofℝ (n).
The value of Math.tanh(x) is the same as the value of (Math.exp(x) - Math.exp(-x)) / (Math.exp(x) + Math.exp(-x)).
21.3.2.36 Math.trunc ( x )
This function returns the integral part of the number x, removing any fractional digits. If x is already integral, the result is x.
It performs the following steps when called:
- Let n be ?
ToNumber (x). - If n is not
finite or n is either+0 𝔽 or-0 𝔽, return n. - If n <
1 𝔽 and n >+0 𝔽, return+0 𝔽. - If n <
-0 𝔽 and n >-1 𝔽, return-0 𝔽. - Return the
integral Number nearest n in the direction of+0 𝔽.
21.4 Date Objects
21.4.1 Overview of Date Objects and Definitions of Abstract Operations
The following
21.4.1.1 Time Values and Time Range
Time measurement in ECMAScript is analogous to time measurement in POSIX, in particular sharing definition in terms of the proleptic Gregorian calendar, an epoch of midnight at the beginning of 1 January 1970 UTC, and an accounting of every day as comprising exactly 86,400 seconds (each of which is 1000 milliseconds long).
An ECMAScript time value
Time values do not account for UTC leap seconds—there are no time values representing instants within positive leap seconds, and there are time values representing instants removed from the UTC timeline by negative leap seconds. However, the definition of time values nonetheless yields piecewise alignment with UTC, with discontinuities only at leap second boundaries and zero difference outside of leap seconds.
A Number can exactly represent all
The exact moment of midnight at the beginning of 1 January 1970 UTC is represented by the time value
In the proleptic Gregorian calendar, leap years are precisely those which are both divisible by 4 and either divisible by 400 or not divisible by 100.
The 400 year cycle of the proleptic Gregorian calendar contains 97 leap years. This yields an average of 365.2425 days per year, which is 31,556,952,000 milliseconds. Therefore, the maximum range a Number could represent exactly with millisecond precision is approximately -285,426 to 285,426 years relative to 1970. The smaller range supported by a time value as specified in this section is approximately -273,790 to 273,790 years relative to 1970.
21.4.1.2 Time-related Constants
These constants are referenced by algorithms in the following sections.
21.4.1.3 Day ( t )
The abstract operation Day takes argument t (a
21.4.1.4 TimeWithinDay ( t )
The abstract operation TimeWithinDay takes argument t (a
21.4.1.5 DaysInYear ( y )
The abstract operation DaysInYear takes argument y (an
21.4.1.6 DayFromYear ( y )
The abstract operation DayFromYear takes argument y (an
- Let ry be
ℝ (y). - NOTE: In the following steps, numYears1, numYears4, numYears100, and numYears400 represent the number of years divisible by 1, 4, 100, and 400, respectively, that occur between the
epoch and the start of year y. The number is negative if y is before theepoch . - Let numYears1 be (ry - 1970).
- Let numYears4 be
floor ((ry - 1969) / 4). - Let numYears100 be
floor ((ry - 1901) / 100). - Let numYears400 be
floor ((ry - 1601) / 400). - Return
𝔽 (365 × numYears1 + numYears4 - numYears100 + numYears400).
21.4.1.7 TimeFromYear ( y )
The abstract operation TimeFromYear takes argument y (an
- Return
msPerDay ×DayFromYear (y).
21.4.1.8 YearFromTime ( t )
The abstract operation YearFromTime takes argument t (a
- Return the largest
integral Number y (closest to +∞) such thatTimeFromYear (y) ≤ t.
21.4.1.9 DayWithinYear ( t )
The abstract operation DayWithinYear takes argument t (a
- Return
Day (t) -DayFromYear (YearFromTime (t)).
21.4.1.10 InLeapYear ( t )
The abstract operation InLeapYear takes argument t (a
- If
DaysInYear (YearFromTime (t)) is366 𝔽, return1 𝔽; else return+0 𝔽.
21.4.1.11 MonthFromTime ( t )
The abstract operation MonthFromTime takes argument t (a
- Let inLeapYear be
InLeapYear (t). - Let dayWithinYear be
DayWithinYear (t). - If dayWithinYear <
31 𝔽, return+0 𝔽. - If dayWithinYear <
59 𝔽 + inLeapYear, return1 𝔽. - If dayWithinYear <
90 𝔽 + inLeapYear, return2 𝔽. - If dayWithinYear <
120 𝔽 + inLeapYear, return3 𝔽. - If dayWithinYear <
151 𝔽 + inLeapYear, return4 𝔽. - If dayWithinYear <
181 𝔽 + inLeapYear, return5 𝔽. - If dayWithinYear <
212 𝔽 + inLeapYear, return6 𝔽. - If dayWithinYear <
243 𝔽 + inLeapYear, return7 𝔽. - If dayWithinYear <
273 𝔽 + inLeapYear, return8 𝔽. - If dayWithinYear <
304 𝔽 + inLeapYear, return9 𝔽. - If dayWithinYear <
334 𝔽 + inLeapYear, return10 𝔽. Assert : dayWithinYear <365 𝔽 + inLeapYear.- Return
11 𝔽.
21.4.1.12 DateFromTime ( t )
The abstract operation DateFromTime takes argument t (a
- Let inLeapYear be
InLeapYear (t). - Let dayWithinYear be
DayWithinYear (t). - Let month be
MonthFromTime (t). - If month is
+0 𝔽, return dayWithinYear +1 𝔽. - If month is
1 𝔽, return dayWithinYear -30 𝔽. - If month is
2 𝔽, return dayWithinYear -58 𝔽 - inLeapYear. - If month is
3 𝔽, return dayWithinYear -89 𝔽 - inLeapYear. - If month is
4 𝔽, return dayWithinYear -119 𝔽 - inLeapYear. - If month is
5 𝔽, return dayWithinYear -150 𝔽 - inLeapYear. - If month is
6 𝔽, return dayWithinYear -180 𝔽 - inLeapYear. - If month is
7 𝔽, return dayWithinYear -211 𝔽 - inLeapYear. - If month is
8 𝔽, return dayWithinYear -242 𝔽 - inLeapYear. - If month is
9 𝔽, return dayWithinYear -272 𝔽 - inLeapYear. - If month is
10 𝔽, return dayWithinYear -303 𝔽 - inLeapYear. Assert : month is11 𝔽.- Return dayWithinYear -
333 𝔽 - inLeapYear.
21.4.1.13 WeekDay ( t )
The abstract operation WeekDay takes argument t (a
21.4.1.14 HourFromTime ( t )
The abstract operation HourFromTime takes argument t (a
21.4.1.15 MinFromTime ( t )
The abstract operation MinFromTime takes argument t (a
- Return
𝔽 (floor (ℝ (t /msPerMinute ))modulo MinutesPerHour ).
21.4.1.16 SecFromTime ( t )
The abstract operation SecFromTime takes argument t (a
- Return
𝔽 (floor (ℝ (t /msPerSecond ))modulo SecondsPerMinute ).
21.4.1.17 msFromTime ( t )
The abstract operation msFromTime takes argument t (a
- Return
𝔽 (ℝ (t)modulo ℝ (msPerSecond )).
21.4.1.18 GetUTCEpochNanoseconds ( year, month, day, hour, minute, second, millisecond, microsecond, nanosecond )
The abstract operation GetUTCEpochNanoseconds takes arguments year (an
21.4.1.19 Time Zone Identifiers
Time zones in ECMAScript are represented by time zone identifiers, which are Strings composed entirely of code units in the
A primary time zone identifier is the preferred identifier for an available named time zone. A non-primary time zone identifier is an identifier for an available named time zone that is not a primary time zone identifier. An available named time zone identifier is either a primary time zone identifier or a non-primary time zone identifier. Each available named time zone identifier is associated with exactly one available named time zone. Each available named time zone is associated with exactly one primary time zone identifier and zero or more non-primary time zone identifiers.
ECMAScript implementations must support an available named time zone with the identifier
Implementations that follow the requirements for time zones as described in the ECMA-402 Internationalization API specification are called time zone aware.
Time zone aware implementations must support available named time zones corresponding to the Zone and Link names of the IANA Time Zone Database, and only such names.
In time zone aware implementations, a primary time zone identifier is a Zone name, and a non-primary time zone identifier is a Link name, respectively, in the IANA Time Zone Database except as specifically overridden by
21.4.1.20 GetNamedTimeZoneEpochNanoseconds ( timeZoneIdentifier, year, month, day, hour, minute, second, millisecond, microsecond, nanosecond )
The
When the input represents a local time occurring more than once because of a negative time zone transition (e.g. when daylight saving time ends or the time zone offset is decreased due to a time zone rule change), the returned
The default implementation of GetNamedTimeZoneEpochNanoseconds, to be used for ECMAScript implementations that do not include local political rules for any time zones, performs the following steps when called:
Assert : timeZoneIdentifier is"UTC" .- Let epochNanoseconds be
GetUTCEpochNanoseconds (year, month, day, hour, minute, second, millisecond, microsecond, nanosecond). - Return « epochNanoseconds ».
It is required for
1:30 AM on 5 November 2017 in America/New_York is repeated twice, so GetNamedTimeZoneEpochNanoseconds(
2:30 AM on 12 March 2017 in America/New_York does not exist, so GetNamedTimeZoneEpochNanoseconds(
21.4.1.21 GetNamedTimeZoneOffsetNanoseconds ( timeZoneIdentifier, epochNanoseconds )
The
The returned
The default implementation of GetNamedTimeZoneOffsetNanoseconds, to be used for ECMAScript implementations that do not include local political rules for any time zones, performs the following steps when called:
Assert : timeZoneIdentifier is"UTC" .- Return 0.
Time zone offset values may be positive or negative.
21.4.1.22 Time Zone Identifier Record
A Time Zone Identifier Record is a
Time Zone Identifier Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Identifier]] | a String | An |
| [[PrimaryIdentifier]] | a String | The |
If [[Identifier]] is a
21.4.1.23 AvailableNamedTimeZoneIdentifiers ( )
The
- If the implementation does not include local political rules for any time zones, then
- Return « the
Time Zone Identifier Record { [[Identifier]]:"UTC" , [[PrimaryIdentifier]]:"UTC" } ».
- Return « the
- Let identifiers be the
List of uniqueavailable named time zone identifiers , sorted according tolexicographic code unit order . - Let result be a new empty
List . - For each element identifier of identifiers, do
- Let primary be identifier.
- If identifier is a
non-primary time zone identifier in this implementation and identifier is not"UTC" , then- Set primary to the
primary time zone identifier associated with identifier. - NOTE: An implementation may need to resolve identifier iteratively to obtain the
primary time zone identifier .
- Set primary to the
- Let record be the
Time Zone Identifier Record { [[Identifier]]: identifier, [[PrimaryIdentifier]]: primary }. - Append record to result.
Assert : result contains aTime Zone Identifier Record r such that r.[[Identifier]] is"UTC" and r.[[PrimaryIdentifier]] is"UTC" .- Return result.
21.4.1.24 SystemTimeZoneIdentifier ( )
The
- If the implementation only supports the UTC time zone, return
"UTC" . - Let systemTimeZoneString be the String representing the
host environment 's current time zone, either aprimary time zone identifier or anoffset time zone identifier. - Return systemTimeZoneString.
To ensure the level of functionality that implementations commonly provide in the methods of the Date object, it is recommended that SystemTimeZoneIdentifier return an IANA time zone name corresponding to the
For example, if the
21.4.1.25 LocalTime ( t )
The abstract operation LocalTime takes argument t (a
- Let systemTimeZoneIdentifier be
SystemTimeZoneIdentifier (). - If
IsTimeZoneOffsetString (systemTimeZoneIdentifier) istrue , then- Let offsetNs be
ParseTimeZoneOffsetString (systemTimeZoneIdentifier).
- Let offsetNs be
- Else,
- Let offsetNs be
GetNamedTimeZoneOffsetNanoseconds (systemTimeZoneIdentifier,ℤ (ℝ (t) × 106)).
- Let offsetNs be
- Let offsetMs be
truncate (offsetNs / 106). - Return t +
𝔽 (offsetMs).
If political rules for the local time t are not available within the implementation, the result is t because
It is required for
Two different input
21.4.1.26 UTC ( t )
The abstract operation UTC takes argument t (a Number) and returns a
- If t is not
finite , returnNaN . - Let systemTimeZoneIdentifier be
SystemTimeZoneIdentifier (). - If
IsTimeZoneOffsetString (systemTimeZoneIdentifier) istrue , then- Let offsetNs be
ParseTimeZoneOffsetString (systemTimeZoneIdentifier).
- Let offsetNs be
- Else,
- Let possibleInstants be
GetNamedTimeZoneEpochNanoseconds (systemTimeZoneIdentifier,ℝ (YearFromTime (t)),ℝ (MonthFromTime (t)) + 1,ℝ (DateFromTime (t)),ℝ (HourFromTime (t)),ℝ (MinFromTime (t)),ℝ (SecFromTime (t)),ℝ (msFromTime (t)), 0, 0). - NOTE: The following steps ensure that when t represents local time repeating multiple times at a negative time zone transition (e.g. when the daylight saving time ends or the time zone offset is decreased due to a time zone rule change) or skipped local time at a positive time zone transition (e.g. when the daylight saving time starts or the time zone offset is increased due to a time zone rule change), t is interpreted using the time zone offset before the transition.
- If possibleInstants is not empty, then
- Let disambiguatedInstant be possibleInstants[0].
- Else,
- NOTE: t represents a local time skipped at a positive time zone transition (e.g. due to daylight saving time starting or a time zone rule change increasing the UTC offset).
- Let possibleInstantsBefore be
GetNamedTimeZoneEpochNanoseconds (systemTimeZoneIdentifier,ℝ (YearFromTime (tBefore)),ℝ (MonthFromTime (tBefore)) + 1,ℝ (DateFromTime (tBefore)),ℝ (HourFromTime (tBefore)),ℝ (MinFromTime (tBefore)),ℝ (SecFromTime (tBefore)),ℝ (msFromTime (tBefore)), 0, 0), where tBefore is the largestintegral Number < t for which possibleInstantsBefore is not empty (i.e., tBefore represents the last local time before the transition). - Let disambiguatedInstant be the last element of possibleInstantsBefore.
- Let offsetNs be
GetNamedTimeZoneOffsetNanoseconds (systemTimeZoneIdentifier, disambiguatedInstant).
- Let possibleInstants be
- Let offsetMs be
truncate (offsetNs / 106). - Return t -
𝔽 (offsetMs).
Input t is nominally a
If political rules for the local time t are not available within the implementation, the result is t because
It is required for
1:30 AM on 5 November 2017 in America/New_York is repeated twice (fall backward), but it must be interpreted as 1:30 AM UTC-04 instead of 1:30 AM UTC-05.
In UTC(
2:30 AM on 12 March 2017 in America/New_York does not exist, but it must be interpreted as 2:30 AM UTC-05 (equivalent to 3:30 AM UTC-04).
In UTC(
21.4.1.27 MakeTime ( hour, min, sec, ms )
The abstract operation MakeTime takes arguments hour (a Number), min (a Number), sec (a Number), and ms (a Number) and returns a Number. It calculates a number of milliseconds. It performs the following steps when called:
- If hour is not
finite , min is notfinite , sec is notfinite , or ms is notfinite , returnNaN . - Let h be
𝔽 (!ToIntegerOrInfinity (hour)). - Let m be
𝔽 (!ToIntegerOrInfinity (min)). - Let s be
𝔽 (!ToIntegerOrInfinity (sec)). - Let milli be
𝔽 (!ToIntegerOrInfinity (ms)). - Return ((h ×
msPerHour + m ×msPerMinute ) + s ×msPerSecond ) + milli.
The arithmetic in MakeTime is floating-point arithmetic, which is not associative, so the operations must be performed in the correct order.
21.4.1.28 MakeDay ( year, month, date )
The abstract operation MakeDay takes arguments year (a Number), month (a Number), and date (a Number) and returns a Number. It calculates a number of days. It performs the following steps when called:
- If year is not
finite , month is notfinite , or date is notfinite , returnNaN . - Let y be
𝔽 (!ToIntegerOrInfinity (year)). - Let m be
𝔽 (!ToIntegerOrInfinity (month)). - Let dt be
𝔽 (!ToIntegerOrInfinity (date)). - Let ym be y +
𝔽 (floor (ℝ (m) / 12)). - If ym is not
finite , returnNaN . - Let mn be
𝔽 (ℝ (m)modulo 12). - Find a
finite time value t such thatYearFromTime (t) is ym,MonthFromTime (t) is mn, andDateFromTime (t) is1 𝔽; but if this is not possible (because some argument is out of range), returnNaN . - Return
Day (t) + dt -1 𝔽.
21.4.1.29 MakeDate ( day, time )
The abstract operation MakeDate takes arguments day (a Number) and time (a Number) and returns a Number. It calculates a number of milliseconds. It performs the following steps when called:
21.4.1.30 MakeFullYear ( year )
The abstract operation MakeFullYear takes argument year (a Number) and returns an
- If year is
NaN , returnNaN . - Let truncated be !
ToIntegerOrInfinity (year). - If truncated is in the
inclusive interval from 0 to 99, return1900 𝔽 +𝔽 (truncated). - Return
𝔽 (truncated).
21.4.1.31 TimeClip ( time )
The abstract operation TimeClip takes argument time (a Number) and returns a Number. It calculates a number of milliseconds. It performs the following steps when called:
- If time is not
finite , returnNaN . - If
abs (ℝ (time)) > 8.64 × 1015, returnNaN . - Return
𝔽 (!ToIntegerOrInfinity (time)).
21.4.1.32 Date Time String Format
ECMAScript defines a string interchange format for date-times based upon a simplification of the ISO 8601 calendar date extended format. The format is as follows: YYYY-MM-DDTHH:mm:ss.sssZ
Where the elements are as follows:
YYYY
|
is the year in the proleptic Gregorian calendar as four decimal digits from 0000 to 9999, or as an |
-
|
|
MM
|
is the month of the year as two decimal digits from 01 (January) to 12 (December). |
DD
|
is the day of the month as two decimal digits from 01 to 31. |
T
|
|
HH
|
is the number of complete hours that have passed since midnight as two decimal digits from 00 to 24. |
:
|
|
mm
|
is the number of complete minutes since the start of the hour as two decimal digits from 00 to 59. |
ss
|
is the number of complete seconds since the start of the minute as two decimal digits from 00 to 59. |
.
|
|
sss
|
is the number of complete milliseconds since the start of the second as three decimal digits. |
Z
|
is the UTC offset representation specified as HH:mm (a subset of the |
This format includes date-only forms:
YYYY
YYYY-MM
YYYY-MM-DD
It also includes “date-time” forms that consist of one of the above date-only forms immediately followed by one of the following time forms with an optional UTC offset representation appended:
THH:mm
THH:mm:ss
THH:mm:ss.sss
A string containing out-of-bounds or nonconforming elements is not a valid instance of this format.
As every day both starts and ends with midnight, the two notations 00:00 and 24:00 are available to distinguish the two midnights that can be associated with one date. This means that the following two notations refer to exactly the same point in time: 1995-02-04T24:00 and 1995-02-05T00:00. This interpretation of the latter form as "end of a calendar day" is consistent with ISO 8601, even though that specification reserves it for describing time intervals and does not permit it within representations of single points in time.
There exists no international standard that specifies abbreviations for civil time zones like CET, EST, etc. and sometimes the same abbreviation is even used for two very different time zones. For this reason, both ISO 8601 and this format specify numeric representations of time zone offsets.
21.4.1.32.1 Expanded Years
Covering the full Date.parse
Examples of date-
| -271821-04-20T00:00:00Z | 271822 B.C. |
| -000001-01-01T00:00:00Z | 2 B.C. |
| +000000-01-01T00:00:00Z | 1 B.C. |
| +000001-01-01T00:00:00Z | 1 A.D. |
| +001970-01-01T00:00:00Z | 1970 A.D. |
| +002009-12-15T00:00:00Z | 2009 A.D. |
| +275760-09-13T00:00:00Z | 275760 A.D. |
21.4.1.33 Time Zone Offset String Format
ECMAScript defines a string interchange format for UTC offsets, derived from ISO 8601. The format is described by the following grammar.
Syntax
21.4.1.33.1 IsTimeZoneOffsetString ( offsetString )
The abstract operation IsTimeZoneOffsetString takes argument offsetString (a String) and returns a Boolean. The return value indicates whether offsetString conforms to the grammar given by
21.4.1.33.2 ParseTimeZoneOffsetString ( offsetString )
The abstract operation ParseTimeZoneOffsetString takes argument offsetString (a String) and returns an
- Let parseResult be
ParseText (offsetString,UTCOffset ). Assert : parseResult is not aList of errors.Assert : parseResult contains aASCIISign Parse Node .- Let parsedSign be the
source text matched by theASCIISign Parse Node contained within parseResult. - If parsedSign is the single code point U+002D (HYPHEN-MINUS), then
- Let sign be -1.
- Else,
- Let sign be 1.
- NOTE: Applications of
StringToNumber below do not lose precision, since each of the parsed values is guaranteed to be a sufficiently short string of decimal digits. Assert : parseResult contains anHour Parse Node .- Let parsedHours be the
source text matched by theHour Parse Node contained within parseResult. - Let hours be
ℝ (StringToNumber (CodePointsToString (parsedHours))). - If parseResult does not contain a
MinuteSecond Parse Node , then- Let minutes be 0.
- Else,
- Let parsedMinutes be the
source text matched by the firstMinuteSecond Parse Node contained within parseResult. - Let minutes be
ℝ (StringToNumber (CodePointsToString (parsedMinutes))).
- Let parsedMinutes be the
- If parseResult does not contain two
MinuteSecond Parse Nodes , then- Let seconds be 0.
- Else,
- Let parsedSeconds be the
source text matched by the secondMinuteSecond Parse Node contained within parseResult. - Let seconds be
ℝ (StringToNumber (CodePointsToString (parsedSeconds))).
- Let parsedSeconds be the
- If parseResult does not contain a
TemporalDecimalFraction Parse Node , then- Let nanoseconds be 0.
- Else,
- Let parsedFraction be the
source text matched by theTemporalDecimalFraction Parse Node contained within parseResult. - Let fraction be the
string-concatenation ofCodePointsToString (parsedFraction) and"000000000" . - Let nanosecondsString be the
substring of fraction from 1 to 10. - Let nanoseconds be
ℝ (StringToNumber (nanosecondsString)).
- Let parsedFraction be the
- Return sign × (((hours × 60 + minutes) × 60 + seconds) × 109 + nanoseconds).
21.4.2 The Date Constructor
The Date
- is %Date%.
- is the initial value of the
"Date" property of theglobal object . - creates and initializes a new Date when called as a
constructor . - returns a String representing the current time (UTC) when called as a function rather than as a
constructor . - is a function whose behaviour differs based upon the number and types of its arguments.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Date behaviour must include asupercall to the Dateconstructor to create and initialize the subclass instance with a [[DateValue]] internal slot.
21.4.2.1 Date ( ...values )
This function performs the following steps when called:
- If NewTarget is
undefined , then- Let now be the
time value (UTC) identifying the current time. - Return
ToDateString (now).
- Let now be the
- Let numberOfArgs be the number of elements in values.
- If numberOfArgs = 0, then
- Let dv be the
time value (UTC) identifying the current time.
- Let dv be the
- Else if numberOfArgs = 1, then
- Let value be values[0].
- If value
is an Object and value has a [[DateValue]] internal slot, then- Let tv be value.[[DateValue]].
- Else,
- Let v be ?
ToPrimitive (value). - If v
is a String , thenAssert : The next step never returns anabrupt completion because vis a String .- Let tv be the result of parsing v as a date, in exactly the same manner as for the
parsemethod (21.4.3.2 ).
- Else,
- Let tv be ?
ToNumber (v).
- Let tv be ?
- Let v be ?
- Let dv be
TimeClip (tv).
- Else,
Assert : numberOfArgs ≥ 2.- Let y be ?
ToNumber (values[0]). - Let m be ?
ToNumber (values[1]). - If numberOfArgs > 2, let dt be ?
ToNumber (values[2]); else let dt be1 𝔽. - If numberOfArgs > 3, let h be ?
ToNumber (values[3]); else let h be+0 𝔽. - If numberOfArgs > 4, let min be ?
ToNumber (values[4]); else let min be+0 𝔽. - If numberOfArgs > 5, let s be ?
ToNumber (values[5]); else let s be+0 𝔽. - If numberOfArgs > 6, let milli be ?
ToNumber (values[6]); else let milli be+0 𝔽. - Let yr be
MakeFullYear (y). - Let finalDate be
MakeDate (MakeDay (yr, m, dt),MakeTime (h, min, s, milli)). - Let dv be
TimeClip (UTC (finalDate)).
- Let O be ?
OrdinaryCreateFromConstructor (NewTarget,"%Date.prototype%" , « [[DateValue]] »). - Set O.[[DateValue]] to dv.
- Return O.
21.4.3 Properties of the Date Constructor
The Date
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"length" property whose value is7 𝔽. - has the following properties:
21.4.3.1 Date.now ( )
This function returns the
21.4.3.2 Date.parse ( string )
This function applies the
If the String conforms to the MM or DD elements are absent, HH, mm, or ss elements are absent, sss element is absent,
If x is any Date whose milliseconds amount is zero within a particular implementation of ECMAScript, then all of the following expressions should produce the same numeric value in that implementation, if all the properties referenced have their initial values:
x.valueOf()
Date.parse(x.toString())
Date.parse(x.toUTCString())
Date.parse(x.toISOString())However, the expression
Date.parse(x.toLocaleString())is not required to produce the same Number value as the preceding three expressions and, in general, the value produced by this function is toString or toUTCString method.
21.4.3.3 Date.prototype
The initial value of Date.prototype is the
This property has the attributes { [[Writable]]:
21.4.3.4 Date.UTC ( year [ , month [ , date [ , hours [ , minutes [ , seconds [ , ms ] ] ] ] ] ] )
This function performs the following steps when called:
- Let y be ?
ToNumber (year). - If month is present, let m be ?
ToNumber (month); else let m be+0 𝔽. - If date is present, let dt be ?
ToNumber (date); else let dt be1 𝔽. - If hours is present, let h be ?
ToNumber (hours); else let h be+0 𝔽. - If minutes is present, let min be ?
ToNumber (minutes); else let min be+0 𝔽. - If seconds is present, let s be ?
ToNumber (seconds); else let s be+0 𝔽. - If ms is present, let milli be ?
ToNumber (ms); else let milli be+0 𝔽. - Let yr be
MakeFullYear (y). - Return
TimeClip (MakeDate (MakeDay (yr, m, dt),MakeTime (h, min, s, milli))).
The
This function differs from the Date
21.4.4 Properties of the Date Prototype Object
The Date prototype object:
- is %Date.prototype%.
- is itself an
ordinary object . - is not a Date instance and does not have a [[DateValue]] internal slot.
- has a [[Prototype]] internal slot whose value is
%Object.prototype% .
Unless explicitly defined otherwise, the methods of the Date prototype object defined below are not generic and the
21.4.4.1 Date.prototype.constructor
The initial value of Date.prototype.constructor is
21.4.4.2 Date.prototype.getDate ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
DateFromTime (LocalTime (t)).
21.4.4.3 Date.prototype.getDay ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
WeekDay (LocalTime (t)).
21.4.4.4 Date.prototype.getFullYear ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
YearFromTime (LocalTime (t)).
21.4.4.5 Date.prototype.getHours ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
HourFromTime (LocalTime (t)).
21.4.4.6 Date.prototype.getMilliseconds ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
msFromTime (LocalTime (t)).
21.4.4.7 Date.prototype.getMinutes ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
MinFromTime (LocalTime (t)).
21.4.4.8 Date.prototype.getMonth ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
MonthFromTime (LocalTime (t)).
21.4.4.9 Date.prototype.getSeconds ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
SecFromTime (LocalTime (t)).
21.4.4.10 Date.prototype.getTime ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Return dateObject.[[DateValue]].
21.4.4.11 Date.prototype.getTimezoneOffset ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return (t -
LocalTime (t)) /msPerMinute .
21.4.4.12 Date.prototype.getUTCDate ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
DateFromTime (t).
21.4.4.13 Date.prototype.getUTCDay ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
WeekDay (t).
21.4.4.14 Date.prototype.getUTCFullYear ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
YearFromTime (t).
21.4.4.15 Date.prototype.getUTCHours ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
HourFromTime (t).
21.4.4.16 Date.prototype.getUTCMilliseconds ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
msFromTime (t).
21.4.4.17 Date.prototype.getUTCMinutes ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
MinFromTime (t).
21.4.4.18 Date.prototype.getUTCMonth ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
MonthFromTime (t).
21.4.4.19 Date.prototype.getUTCSeconds ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , returnNaN . - Return
SecFromTime (t).
21.4.4.20 Date.prototype.setDate ( date )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let dt be ?
ToNumber (date). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - Let newDate be
MakeDate (MakeDay (YearFromTime (t),MonthFromTime (t), dt),TimeWithinDay (t)). - Let u be
TimeClip (UTC (newDate)). - Set dateObject.[[DateValue]] to u.
- Return u.
21.4.4.21 Date.prototype.setFullYear ( year [ , month [ , date ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let y be ?
ToNumber (year). - If t is
NaN , set t to+0 𝔽; otherwise, set t toLocalTime (t). - If month is not present, let m be
MonthFromTime (t); otherwise, let m be ?ToNumber (month). - If date is not present, let dt be
DateFromTime (t); otherwise, let dt be ?ToNumber (date). - Let newDate be
MakeDate (MakeDay (y, m, dt),TimeWithinDay (t)). - Let u be
TimeClip (UTC (newDate)). - Set dateObject.[[DateValue]] to u.
- Return u.
The
If month is not present, this method behaves as if month was present with the value getMonth(). If date is not present, it behaves as if date was present with the value getDate().
21.4.4.22 Date.prototype.setHours ( hour [ , min [ , sec [ , ms ] ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let h be ?
ToNumber (hour). - If min is present, let m be ?
ToNumber (min). - If sec is present, let s be ?
ToNumber (sec). - If ms is present, let milli be ?
ToNumber (ms). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - If min is not present, let m be
MinFromTime (t). - If sec is not present, let s be
SecFromTime (t). - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (h, m, s, milli)). - Let u be
TimeClip (UTC (date)). - Set dateObject.[[DateValue]] to u.
- Return u.
The
If min is not present, this method behaves as if min was present with the value getMinutes(). If sec is not present, it behaves as if sec was present with the value getSeconds(). If ms is not present, it behaves as if ms was present with the value getMilliseconds().
21.4.4.23 Date.prototype.setMilliseconds ( ms )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Set ms to ?
ToNumber (ms). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - Let time be
MakeTime (HourFromTime (t),MinFromTime (t),SecFromTime (t), ms). - Let u be
TimeClip (UTC (MakeDate (Day (t), time))). - Set dateObject.[[DateValue]] to u.
- Return u.
21.4.4.24 Date.prototype.setMinutes ( min [ , sec [ , ms ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let m be ?
ToNumber (min). - If sec is present, let s be ?
ToNumber (sec). - If ms is present, let milli be ?
ToNumber (ms). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - If sec is not present, let s be
SecFromTime (t). - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (HourFromTime (t), m, s, milli)). - Let u be
TimeClip (UTC (date)). - Set dateObject.[[DateValue]] to u.
- Return u.
The
If sec is not present, this method behaves as if sec was present with the value getSeconds(). If ms is not present, this behaves as if ms was present with the value getMilliseconds().
21.4.4.25 Date.prototype.setMonth ( month [ , date ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let m be ?
ToNumber (month). - If date is present, let dt be ?
ToNumber (date). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - If date is not present, let dt be
DateFromTime (t). - Let newDate be
MakeDate (MakeDay (YearFromTime (t), m, dt),TimeWithinDay (t)). - Let u be
TimeClip (UTC (newDate)). - Set dateObject.[[DateValue]] to u.
- Return u.
The
If date is not present, this method behaves as if date was present with the value getDate().
21.4.4.26 Date.prototype.setSeconds ( sec [ , ms ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let s be ?
ToNumber (sec). - If ms is present, let milli be ?
ToNumber (ms). - If t is
NaN , returnNaN . - Set t to
LocalTime (t). - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (HourFromTime (t),MinFromTime (t), s, milli)). - Let u be
TimeClip (UTC (date)). - Set dateObject.[[DateValue]] to u.
- Return u.
The
If ms is not present, this method behaves as if ms was present with the value getMilliseconds().
21.4.4.27 Date.prototype.setTime ( time )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be ?
ToNumber (time). - Let v be
TimeClip (t). - Set dateObject.[[DateValue]] to v.
- Return v.
21.4.4.28 Date.prototype.setUTCDate ( date )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let dt be ?
ToNumber (date). - If t is
NaN , returnNaN . - Let newDate be
MakeDate (MakeDay (YearFromTime (t),MonthFromTime (t), dt),TimeWithinDay (t)). - Let v be
TimeClip (newDate). - Set dateObject.[[DateValue]] to v.
- Return v.
21.4.4.29 Date.prototype.setUTCFullYear ( year [ , month [ , date ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- If t is
NaN , set t to+0 𝔽. - Let y be ?
ToNumber (year). - If month is not present, let m be
MonthFromTime (t); otherwise, let m be ?ToNumber (month). - If date is not present, let dt be
DateFromTime (t); otherwise, let dt be ?ToNumber (date). - Let newDate be
MakeDate (MakeDay (y, m, dt),TimeWithinDay (t)). - Let v be
TimeClip (newDate). - Set dateObject.[[DateValue]] to v.
- Return v.
The
If month is not present, this method behaves as if month was present with the value getUTCMonth(). If date is not present, it behaves as if date was present with the value getUTCDate().
21.4.4.30 Date.prototype.setUTCHours ( hour [ , min [ , sec [ , ms ] ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let h be ?
ToNumber (hour). - If min is present, let m be ?
ToNumber (min). - If sec is present, let s be ?
ToNumber (sec). - If ms is present, let milli be ?
ToNumber (ms). - If t is
NaN , returnNaN . - If min is not present, let m be
MinFromTime (t). - If sec is not present, let s be
SecFromTime (t). - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (h, m, s, milli)). - Let v be
TimeClip (date). - Set dateObject.[[DateValue]] to v.
- Return v.
The
If min is not present, this method behaves as if min was present with the value getUTCMinutes(). If sec is not present, it behaves as if sec was present with the value getUTCSeconds(). If ms is not present, it behaves as if ms was present with the value getUTCMilliseconds().
21.4.4.31 Date.prototype.setUTCMilliseconds ( ms )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Set ms to ?
ToNumber (ms). - If t is
NaN , returnNaN . - Let time be
MakeTime (HourFromTime (t),MinFromTime (t),SecFromTime (t), ms). - Let v be
TimeClip (MakeDate (Day (t), time)). - Set dateObject.[[DateValue]] to v.
- Return v.
21.4.4.32 Date.prototype.setUTCMinutes ( min [ , sec [ , ms ] ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let m be ?
ToNumber (min). - If sec is present, let s be ?
ToNumber (sec). - If ms is present, let milli be ?
ToNumber (ms). - If t is
NaN , returnNaN . - If sec is not present, let s be
SecFromTime (t). - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (HourFromTime (t), m, s, milli)). - Let v be
TimeClip (date). - Set dateObject.[[DateValue]] to v.
- Return v.
The
If sec is not present, this method behaves as if sec was present with the value getUTCSeconds(). If ms is not present, it behaves as if ms was present with the value return by getUTCMilliseconds().
21.4.4.33 Date.prototype.setUTCMonth ( month [ , date ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let m be ?
ToNumber (month). - If date is present, let dt be ?
ToNumber (date). - If t is
NaN , returnNaN . - If date is not present, let dt be
DateFromTime (t). - Let newDate be
MakeDate (MakeDay (YearFromTime (t), m, dt),TimeWithinDay (t)). - Let v be
TimeClip (newDate). - Set dateObject.[[DateValue]] to v.
- Return v.
The
If date is not present, this method behaves as if date was present with the value getUTCDate().
21.4.4.34 Date.prototype.setUTCSeconds ( sec [ , ms ] )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let t be dateObject.[[DateValue]].
- Let s be ?
ToNumber (sec). - If ms is present, let milli be ?
ToNumber (ms). - If t is
NaN , returnNaN . - If ms is not present, let milli be
msFromTime (t). - Let date be
MakeDate (Day (t),MakeTime (HourFromTime (t),MinFromTime (t), s, milli)). - Let v be
TimeClip (date). - Set dateObject.[[DateValue]] to v.
- Return v.
The
If ms is not present, this method behaves as if ms was present with the value getUTCMilliseconds().
21.4.4.35 Date.prototype.toDateString ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let tv be dateObject.[[DateValue]].
- If tv is
NaN , return"Invalid Date" . - Let t be
LocalTime (tv). - Return
DateString (t).
21.4.4.36 Date.prototype.toISOString ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let tv be dateObject.[[DateValue]].
- If tv is
NaN , throw aRangeError exception. Assert : tv is anintegral Number .- If tv corresponds with a year that cannot be represented in the
Date Time String Format , throw aRangeError exception. - Return a String representation of tv in the
Date Time String Format on the UTC time scale, including all format elements and the UTC offset representation"Z" .
21.4.4.37 Date.prototype.toJSON ( key )
This method provides a String representation of a Date for use by JSON.stringify (
It performs the following steps when called:
- Let O be ?
ToObject (this value). - Let tv be ?
ToPrimitive (O,number ). - If tv
is a Number and tv is notfinite , returnnull . - Return ?
Invoke (O,"toISOString" ).
The argument is ignored.
This method is intentionally generic; it does not require that its toISOString method.
21.4.4.38 Date.prototype.toLocaleDateString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method returns a String value. The contents of the String are
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.4.4.39 Date.prototype.toLocaleString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method returns a String value. The contents of the String are
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.4.4.40 Date.prototype.toLocaleTimeString ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method returns a String value. The contents of the String are
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.4.4.41 Date.prototype.toString ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let tv be dateObject.[[DateValue]].
- Return
ToDateString (tv).
For any Date d such that d.[[DateValue]] is evenly divisible by 1000, the result of Date.parse(d.toString()) = d.valueOf(). See
This method is not generic; it throws a
21.4.4.41.1 TimeString ( tv )
The abstract operation TimeString takes argument tv (a Number, but not
- Let hour be
ToZeroPaddedDecimalString (ℝ (HourFromTime (tv)), 2). - Let minute be
ToZeroPaddedDecimalString (ℝ (MinFromTime (tv)), 2). - Let second be
ToZeroPaddedDecimalString (ℝ (SecFromTime (tv)), 2). - Return the
string-concatenation of hour,":" , minute,":" , second, the code unit 0x0020 (SPACE), and"GMT" .
21.4.4.41.2 DateString ( tv )
The abstract operation DateString takes argument tv (a Number, but not
- Let weekday be the Name of the entry in
Table 65 with the NumberWeekDay (tv). - Let month be the Name of the entry in
Table 66 with the NumberMonthFromTime (tv). - Let day be
ToZeroPaddedDecimalString (ℝ (DateFromTime (tv)), 2). - Let yv be
YearFromTime (tv). - If yv is
+0 𝔽 or yv >+0 𝔽, let yearSign be the empty String; otherwise, let yearSign be"-" . - Let paddedYear be
ToZeroPaddedDecimalString (abs (ℝ (yv)), 4). - Return the
string-concatenation of weekday, the code unit 0x0020 (SPACE), month, the code unit 0x0020 (SPACE), day, the code unit 0x0020 (SPACE), yearSign, and paddedYear.
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21.4.4.41.3 TimeZoneString ( tv )
The abstract operation TimeZoneString takes argument tv (an
- Let systemTimeZoneIdentifier be
SystemTimeZoneIdentifier (). - If
IsTimeZoneOffsetString (systemTimeZoneIdentifier) istrue , then- Let offsetNs be
ParseTimeZoneOffsetString (systemTimeZoneIdentifier).
- Let offsetNs be
- Else,
- Let offsetNs be
GetNamedTimeZoneOffsetNanoseconds (systemTimeZoneIdentifier,ℤ (ℝ (tv) × 106)).
- Let offsetNs be
- Let offset be
𝔽 (truncate (offsetNs / 106)). - If offset is
+0 𝔽 or offset >+0 𝔽, then- Let offsetSign be
"+" . - Let absOffset be offset.
- Let offsetSign be
- Else,
- Let offsetSign be
"-" . - Let absOffset be -offset.
- Let offsetSign be
- Let offsetMin be
ToZeroPaddedDecimalString (ℝ (MinFromTime (absOffset)), 2). - Let offsetHour be
ToZeroPaddedDecimalString (ℝ (HourFromTime (absOffset)), 2). - Let tzName be an
implementation-defined string that is either the empty String or thestring-concatenation of the code unit 0x0020 (SPACE), the code unit 0x0028 (LEFT PARENTHESIS), animplementation-defined timezone name, and the code unit 0x0029 (RIGHT PARENTHESIS). - Return the
string-concatenation of offsetSign, offsetHour, offsetMin, and tzName.
21.4.4.41.4 ToDateString ( tv )
The abstract operation ToDateString takes argument tv (an
- If tv is
NaN , return"Invalid Date" . - Let t be
LocalTime (tv). - Return the
string-concatenation ofDateString (t), the code unit 0x0020 (SPACE),TimeString (t), andTimeZoneString (tv).
21.4.4.42 Date.prototype.toTimeString ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let tv be dateObject.[[DateValue]].
- If tv is
NaN , return"Invalid Date" . - Let t be
LocalTime (tv). - Return the
string-concatenation ofTimeString (t) andTimeZoneString (tv).
21.4.4.43 Date.prototype.toUTCString ( )
This method returns a String value representing the instant in time corresponding to the
It performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Let tv be dateObject.[[DateValue]].
- If tv is
NaN , return"Invalid Date" . - Let weekday be the Name of the entry in
Table 65 with the NumberWeekDay (tv). - Let month be the Name of the entry in
Table 66 with the NumberMonthFromTime (tv). - Let day be
ToZeroPaddedDecimalString (ℝ (DateFromTime (tv)), 2). - Let yv be
YearFromTime (tv). - If yv is
+0 𝔽 or yv >+0 𝔽, let yearSign be the empty String; otherwise, let yearSign be"-" . - Let paddedYear be
ToZeroPaddedDecimalString (abs (ℝ (yv)), 4). - Return the
string-concatenation of weekday,"," , the code unit 0x0020 (SPACE), day, the code unit 0x0020 (SPACE), month, the code unit 0x0020 (SPACE), yearSign, paddedYear, the code unit 0x0020 (SPACE), andTimeString (tv).
21.4.4.44 Date.prototype.valueOf ( )
This method performs the following steps when called:
- Let dateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject, [[DateValue]]). - Return dateObject.[[DateValue]].
21.4.4.45 Date.prototype [ %Symbol.toPrimitive% ] ( hint )
This method is called by ECMAScript language operators to convert a Date to a primitive value. The allowed values for hint are
It performs the following steps when called:
- Let O be the
this value. - If O
is not an Object , throw aTypeError exception. - If hint is either
"string" or"default" , then- Let tryFirst be
string .
- Let tryFirst be
- Else if hint is
"number" , then- Let tryFirst be
number .
- Let tryFirst be
- Else,
- Throw a
TypeError exception.
- Throw a
- Return ?
OrdinaryToPrimitive (O, tryFirst).
This property has the attributes { [[Writable]]:
The value of the
21.4.5 Properties of Date Instances
Date instances are
22 Text Processing
22.1 String Objects
22.1.1 The String Constructor
The String
- is %String%.
- is the initial value of the
"String" property of theglobal object . - creates and initializes a new String object when called as a
constructor . - performs a type conversion when called as a function rather than as a
constructor . - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified String behaviour must include asupercall to the Stringconstructor to create and initialize the subclass instance with a [[StringData]] internal slot.
22.1.1.1 String ( value )
This function performs the following steps when called:
- If value is not present, then
- Let s be the empty String.
- Else,
- If NewTarget is
undefined and valueis a Symbol , returnSymbolDescriptiveString (value). - Let s be ?
ToString (value).
- If NewTarget is
- If NewTarget is
undefined , return s. - Return
StringCreate (s, ?GetPrototypeFromConstructor (NewTarget,"%String.prototype%" )).
22.1.2 Properties of the String Constructor
The String
- has a [[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
22.1.2.1 String.fromCharCode ( ...codeUnits )
This function may be called with any number of arguments which form the rest parameter codeUnits.
It performs the following steps when called:
- Let result be the empty String.
- For each element next of codeUnits, do
- Let nextCU be the code unit whose numeric value is
ℝ (?ToUint16 (next)). - Set result to the
string-concatenation of result and nextCU.
- Let nextCU be the code unit whose numeric value is
- Return result.
The
22.1.2.2 String.fromCodePoint ( ...codePoints )
This function may be called with any number of arguments which form the rest parameter codePoints.
It performs the following steps when called:
- Let result be the empty String.
- For each element next of codePoints, do
- Let nextCP be ?
ToNumber (next). - If nextCP is not an
integral Number , throw aRangeError exception. - If
ℝ (nextCP) < 0 orℝ (nextCP) > 0x10FFFF, throw aRangeError exception. - Set result to the
string-concatenation of result andUTF16EncodeCodePoint (ℝ (nextCP)).
- Let nextCP be ?
Assert : If codePoints is empty, then result is the empty String.- Return result.
The
22.1.2.3 String.prototype
The initial value of String.prototype is the
This property has the attributes { [[Writable]]:
22.1.2.4 String.raw ( template, ...substitutions )
This function may be called with a variable number of arguments. The first argument is template and the remainder of the arguments form the
It performs the following steps when called:
- Let substitutionCount be the number of elements in substitutions.
- Let cooked be ?
ToObject (template). - Let literals be ?
ToObject (?Get (cooked,"raw" )). - Let literalCount be ?
LengthOfArrayLike (literals). - If literalCount ≤ 0, return the empty String.
- Let R be the empty String.
- Let nextIndex be 0.
- Repeat,
- Let nextLiteralVal be ?
Get (literals, !ToString (𝔽 (nextIndex))). - Let nextLiteral be ?
ToString (nextLiteralVal). - Set R to the
string-concatenation of R and nextLiteral. - If nextIndex + 1 = literalCount, return R.
- If nextIndex < substitutionCount, then
- Let nextSubVal be substitutions[nextIndex].
- Let nextSub be ?
ToString (nextSubVal). - Set R to the
string-concatenation of R and nextSub.
- Set nextIndex to nextIndex + 1.
- Let nextLiteralVal be ?
This function is intended for use as a tag function of a Tagged Template (
22.1.3 Properties of the String Prototype Object
The String prototype object:
- is %String.prototype%.
is a String exotic object and has the internal methods specified for such objects.- has a [[StringData]] internal slot whose value is the empty String.
- has a
"length" property whose initial value is+0 𝔽 and whose attributes are { [[Writable]]:false , [[Enumerable]]:false , [[Configurable]]:false }. - has a [[Prototype]] internal slot whose value is
%Object.prototype% .
Unless explicitly stated otherwise, the methods of the String prototype object defined below are not generic and the
22.1.3.1 String.prototype.at ( index )
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let len be the length of S.
- Let relativeIndex be ?
ToIntegerOrInfinity (index). - If relativeIndex ≥ 0, then
- Let k be relativeIndex.
- Else,
- Let k be len + relativeIndex.
- If k < 0 or k ≥ len, return
undefined . - Return the
substring of S from k to k + 1.
22.1.3.2 String.prototype.charAt ( pos )
This method returns a single element String containing the code unit at index pos within the String value resulting from converting this object to a String. If there is no element at that index, the result is the empty String. The result
If pos is an x.charAt(pos) is equivalent to the result of x.substring(pos, pos + 1).
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let position be ?
ToIntegerOrInfinity (pos). - Let size be the length of S.
- If position < 0 or position ≥ size, return the empty String.
- Return the
substring of S from position to position + 1.
This method is intentionally generic; it does not require that its
22.1.3.3 String.prototype.charCodeAt ( pos )
This method returns a Number (a non-negative
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let position be ?
ToIntegerOrInfinity (pos). - Let size be the length of S.
- If position < 0 or position ≥ size, return
NaN . - Return the
Number value for the numeric value of the code unit at index position within the String S.
This method is intentionally generic; it does not require that its
22.1.3.4 String.prototype.codePointAt ( pos )
This method returns a non-negative
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let position be ?
ToIntegerOrInfinity (pos). - Let size be the length of S.
- If position < 0 or position ≥ size, return
undefined . - Let cp be
CodePointAt (S, position). - Return
𝔽 (cp.[[CodePoint]]).
This method is intentionally generic; it does not require that its
22.1.3.5 String.prototype.concat ( ...args )
When this method is called it returns the String value consisting of the code units of the
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let R be S.
- For each element next of args, do
- Let nextString be ?
ToString (next). - Set R to the
string-concatenation of R and nextString.
- Let nextString be ?
- Return R.
The
This method is intentionally generic; it does not require that its
22.1.3.6 String.prototype.constructor
The initial value of String.prototype.constructor is
22.1.3.7 String.prototype.endsWith ( searchString [ , endPosition ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let isRegExp be ?
IsRegExp (searchString). - If isRegExp is
true , throw aTypeError exception. - Let searchStr be ?
ToString (searchString). - Let len be the length of S.
- If endPosition is
undefined , let pos be len; else let pos be ?ToIntegerOrInfinity (endPosition). - Let end be the result of
clamping pos between 0 and len. - Let searchLength be the length of searchStr.
- If searchLength = 0, return
true . - Let start be end - searchLength.
- If start < 0, return
false . - Let substring be the
substring of S from start to end. - If substring is searchStr, return
true . - Return
false .
This method returns
Throwing an exception if the first argument is a RegExp is specified in order to allow future editions to define extensions that allow such argument values.
This method is intentionally generic; it does not require that its
22.1.3.8 String.prototype.includes ( searchString [ , position ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let isRegExp be ?
IsRegExp (searchString). - If isRegExp is
true , throw aTypeError exception. - Let searchStr be ?
ToString (searchString). - Let pos be ?
ToIntegerOrInfinity (position). Assert : If position isundefined , then pos is 0.- Let len be the length of S.
- Let start be the result of
clamping pos between 0 and len. - Let index be
StringIndexOf (S, searchStr, start). - If index is
not-found , returnfalse . - Return
true .
If searchString appears as a
Throwing an exception if the first argument is a RegExp is specified in order to allow future editions to define extensions that allow such argument values.
This method is intentionally generic; it does not require that its
22.1.3.9 String.prototype.indexOf ( searchString [ , position ] )
If searchString appears as a
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let searchStr be ?
ToString (searchString). - Let pos be ?
ToIntegerOrInfinity (position). Assert : If position isundefined , then pos is 0.- Let len be the length of S.
- Let start be the result of
clamping pos between 0 and len. - Let result be
StringIndexOf (S, searchStr, start). - If result is
not-found , return-1 𝔽. - Return
𝔽 (result).
This method is intentionally generic; it does not require that its
22.1.3.10 String.prototype.isWellFormed ( )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Return
IsStringWellFormedUnicode (S).
22.1.3.11 String.prototype.lastIndexOf ( searchString [ , position ] )
If searchString appears as a
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let searchStr be ?
ToString (searchString). - Let numPos be ?
ToNumber (position). Assert : If position isundefined , then numPos isNaN .- If numPos is
NaN , let pos be +∞; otherwise, let pos be !ToIntegerOrInfinity (numPos). - Let len be the length of S.
- Let searchLen be the length of searchStr.
- Let start be the result of
clamping pos between 0 and len - searchLen. - Let result be
StringLastIndexOf (S, searchStr, start). - If result is
not-found , return-1 𝔽. - Return
𝔽 (result).
This method is intentionally generic; it does not require that its
22.1.3.12 String.prototype.localeCompare ( that [ , reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method returns a Number other than
Before performing the comparisons, this method performs the following steps to prepare the Strings:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let thatValue be ?
ToString (that).
The meaning of the optional second and third parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not assign any other interpretation to those parameter positions.
The actual return values are
This method itself is not directly suitable as an argument to Array.prototype.sort because the latter requires a function of two arguments.
This method may rely on whatever language- and/or locale-sensitive comparison functionality is available to the ECMAScript environment from the
// Å ANGSTROM SIGN vs.
// Å LATIN CAPITAL LETTER A + COMBINING RING ABOVE
"\u212B".localeCompare("A\u030A")
// Ω OHM SIGN vs.
// Ω GREEK CAPITAL LETTER OMEGA
"\u2126".localeCompare("\u03A9")
// ṩ LATIN SMALL LETTER S WITH DOT BELOW AND DOT ABOVE vs.
// ṩ LATIN SMALL LETTER S + COMBINING DOT ABOVE + COMBINING DOT BELOW
"\u1E69".localeCompare("s\u0307\u0323")
// ḍ̇ LATIN SMALL LETTER D WITH DOT ABOVE + COMBINING DOT BELOW vs.
// ḍ̇ LATIN SMALL LETTER D WITH DOT BELOW + COMBINING DOT ABOVE
"\u1E0B\u0323".localeCompare("\u1E0D\u0307")
// 가 HANGUL CHOSEONG KIYEOK + HANGUL JUNGSEONG A vs.
// 가 HANGUL SYLLABLE GA
"\u1100\u1161".localeCompare("\uAC00")For a definition and discussion of canonical equivalence see the Unicode Standard, chapters 2 and 3, as well as Unicode Standard Annex #15, Unicode Normalization Forms and Unicode Technical Note #5, Canonical Equivalence in Applications. Also see Unicode Technical Standard #10, Unicode Collation Algorithm.
It is recommended that this method should not honour Unicode compatibility equivalents or compatibility decompositions as defined in the Unicode Standard, chapter 3, section 3.7.
This method is intentionally generic; it does not require that its
22.1.3.13 String.prototype.match ( regexp )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If regexp is neither
undefined nornull , then- Let matcher be ?
GetMethod (regexp,%Symbol.match% ). - If matcher is not
undefined , then- Return ?
Call (matcher, regexp, « O »).
- Return ?
- Let matcher be ?
- Let S be ?
ToString (O). - Let rx be ?
RegExpCreate (regexp,undefined ). - Return ?
Invoke (rx,%Symbol.match% , « S »).
This method is intentionally generic; it does not require that its
22.1.3.14 String.prototype.matchAll ( regexp )
This method performs a regular expression match of the String representing the
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If regexp is neither
undefined nornull , then- Let isRegExp be ?
IsRegExp (regexp). - If isRegExp is
true , then- Let flags be ?
Get (regexp,"flags" ). - Perform ?
RequireObjectCoercible (flags). - If ?
ToString (flags) does not contain"g" , throw aTypeError exception.
- Let flags be ?
- Let matcher be ?
GetMethod (regexp,%Symbol.matchAll% ). - If matcher is not
undefined , then- Return ?
Call (matcher, regexp, « O »).
- Return ?
- Let isRegExp be ?
- Let S be ?
ToString (O). - Let rx be ?
RegExpCreate (regexp,"g" ). - Return ?
Invoke (rx,%Symbol.matchAll% , « S »).
String.prototype.split, String.prototype.matchAll is designed to typically act without mutating its inputs.22.1.3.15 String.prototype.normalize ( [ form ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - If form is
undefined , let f be"NFC" . - Else, let f be ?
ToString (form). - If f is not one of
"NFC" ,"NFD" ,"NFKC" , or"NFKD" , throw aRangeError exception. - Let ns be the String value that is the result of normalizing S into the normalization form named by f as specified in the latest Unicode Standard, Normalization Forms.
- Return ns.
This method is intentionally generic; it does not require that its
22.1.3.16 String.prototype.padEnd ( maxLength [ , fillString ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Return ?
StringPaddingBuiltinsImpl (O, maxLength, fillString,end ).
22.1.3.17 String.prototype.padStart ( maxLength [ , fillString ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Return ?
StringPaddingBuiltinsImpl (O, maxLength, fillString,start ).
22.1.3.17.1 StringPaddingBuiltinsImpl ( O, maxLength, fillString, placement )
The abstract operation StringPaddingBuiltinsImpl takes arguments O (an
- Let S be ?
ToString (O). - Let intMaxLength be
ℝ (?ToLength (maxLength)). - Let stringLength be the length of S.
- If intMaxLength ≤ stringLength, return S.
- If fillString is
undefined , set fillString to the String value consisting solely of the code unit 0x0020 (SPACE). - Else, set fillString to ?
ToString (fillString). - Return
StringPad (S, intMaxLength, fillString, placement).
22.1.3.17.2 StringPad ( S, maxLength, fillString, placement )
The abstract operation StringPad takes arguments S (a String), maxLength (a non-negative
- Let stringLength be the length of S.
- If maxLength ≤ stringLength, return S.
- If fillString is the empty String, return S.
- Let fillLen be maxLength - stringLength.
- Let truncatedStringFiller be the String value consisting of repeated concatenations of fillString truncated to length fillLen.
- If placement is
start , return thestring-concatenation of truncatedStringFiller and S. - Else, return the
string-concatenation of S and truncatedStringFiller.
The argument maxLength will be clamped such that it can be no smaller than the length of S.
The argument fillString defaults to
22.1.3.17.3 ToZeroPaddedDecimalString ( n, minLength )
The abstract operation ToZeroPaddedDecimalString takes arguments n (a non-negative
- Let S be the String representation of n, formatted as a decimal number.
- Return
StringPad (S, minLength,"0" ,start ).
22.1.3.18 String.prototype.repeat ( count )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let n be ?
ToIntegerOrInfinity (count). - If n < 0 or n = +∞, throw a
RangeError exception. - If n = 0, return the empty String.
- Return the String value that is made from n copies of S appended together.
This method creates the String value consisting of the code units of the
This method is intentionally generic; it does not require that its
22.1.3.19 String.prototype.replace ( searchValue, replaceValue )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If searchValue is neither
undefined nornull , then- Let replacer be ?
GetMethod (searchValue,%Symbol.replace% ). - If replacer is not
undefined , then- Return ?
Call (replacer, searchValue, « O, replaceValue »).
- Return ?
- Let replacer be ?
- Let string be ?
ToString (O). - Let searchString be ?
ToString (searchValue). - Let functionalReplace be
IsCallable (replaceValue). - If functionalReplace is
false , then- Set replaceValue to ?
ToString (replaceValue).
- Set replaceValue to ?
- Let searchLength be the length of searchString.
- Let position be
StringIndexOf (string, searchString, 0). - If position is
not-found , return string. - Let preceding be the
substring of string from 0 to position. - Let following be the
substring of string from position + searchLength. - If functionalReplace is
true , then - Else,
Assert : replaceValueis a String .- Let captures be a new empty
List . - Let replacement be !
GetSubstitution (searchString, string, position, captures,undefined , replaceValue).
- Return the
string-concatenation of preceding, replacement, and following.
This method is intentionally generic; it does not require that its
22.1.3.19.1 GetSubstitution ( matched, str, position, captures, namedCaptures, replacementTemplate )
The abstract operation GetSubstitution takes arguments matched (a String), str (a String), position (a non-negative
- Let stringLength be the length of str.
Assert : position ≤ stringLength.- Let result be the empty String.
- Let templateRemainder be replacementTemplate.
- Repeat, while templateRemainder is not the empty String,
- NOTE: The following steps isolate ref (a prefix of templateRemainder), determine refReplacement (its replacement), and then append that replacement to result.
- If templateRemainder starts with
"$$" , then- Let ref be
"$$" . - Let refReplacement be
"$" .
- Let ref be
- Else if templateRemainder starts with
"$`" , then- Let ref be
"$`" . - Let refReplacement be the
substring of str from 0 to position.
- Let ref be
- Else if templateRemainder starts with
"$&" , then- Let ref be
"$&" . - Let refReplacement be matched.
- Let ref be
- Else if templateRemainder starts with
"$'" (0x0024 (DOLLAR SIGN) followed by 0x0027 (APOSTROPHE)), then- Let ref be
"$'" . - Let matchLength be the length of matched.
- Let tailPos be position + matchLength.
- Let refReplacement be the
substring of str frommin (tailPos, stringLength). - NOTE: tailPos can exceed stringLength only if this abstract operation was invoked by a call to the intrinsic
%Symbol.replace% method of%RegExp.prototype% on an object whose"exec" property is not the intrinsic %RegExp.prototype.exec%.
- Let ref be
- Else if templateRemainder starts with
"$" followed by 1 or more decimal digits, then- If templateRemainder starts with
"$" followed by 2 or more decimal digits, let digitCount be 2. Otherwise, let digitCount be 1. - Let digits be the
substring of templateRemainder from 1 to 1 + digitCount. - Let index be
ℝ (StringToNumber (digits)). Assert : 0 ≤ index ≤ 99.- Let captureLen be the number of elements in captures.
- If index > captureLen and digitCount = 2, then
- NOTE: When a two-digit replacement pattern specifies an index exceeding the count of capturing groups, it is treated as a one-digit replacement pattern followed by a literal digit.
- Set digitCount to 1.
- Set digits to the
substring of digits from 0 to 1. - Set index to
ℝ (StringToNumber (digits)).
- Let ref be the
substring of templateRemainder from 0 to 1 + digitCount. - If 1 ≤ index ≤ captureLen, then
- Let capture be captures[index - 1].
- If capture is
undefined , then- Let refReplacement be the empty String.
- Else,
- Let refReplacement be capture.
- Else,
- Let refReplacement be ref.
- If templateRemainder starts with
- Else if templateRemainder starts with
"$<" , then- Let gtPos be
StringIndexOf (templateRemainder,">" , 0). - If gtPos is
not-found or namedCaptures isundefined , then- Let ref be
"$<" . - Let refReplacement be ref.
- Let ref be
- Else,
- Let ref be the
substring of templateRemainder from 0 to gtPos + 1. - Let groupName be the
substring of templateRemainder from 2 to gtPos. Assert : namedCapturesis an Object .- Let capture be ?
Get (namedCaptures, groupName). - If capture is
undefined , then- Let refReplacement be the empty String.
- Else,
- Let refReplacement be ?
ToString (capture).
- Let refReplacement be ?
- Let ref be the
- Let gtPos be
- Else,
- Let ref be the
substring of templateRemainder from 0 to 1. - Let refReplacement be ref.
- Let ref be the
- Let refLength be the length of ref.
- Set templateRemainder to the
substring of templateRemainder from refLength. - Set result to the
string-concatenation of result and refReplacement.
- Return result.
22.1.3.20 String.prototype.replaceAll ( searchValue, replaceValue )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If searchValue is neither
undefined nornull , then- Let isRegExp be ?
IsRegExp (searchValue). - If isRegExp is
true , then- Let flags be ?
Get (searchValue,"flags" ). - Perform ?
RequireObjectCoercible (flags). - If ?
ToString (flags) does not contain"g" , throw aTypeError exception.
- Let flags be ?
- Let replacer be ?
GetMethod (searchValue,%Symbol.replace% ). - If replacer is not
undefined , then- Return ?
Call (replacer, searchValue, « O, replaceValue »).
- Return ?
- Let isRegExp be ?
- Let string be ?
ToString (O). - Let searchString be ?
ToString (searchValue). - Let functionalReplace be
IsCallable (replaceValue). - If functionalReplace is
false , then- Set replaceValue to ?
ToString (replaceValue).
- Set replaceValue to ?
- Let searchLength be the length of searchString.
- Let advanceBy be
max (1, searchLength). - Let matchPositions be a new empty
List . - Let position be
StringIndexOf (string, searchString, 0). - Repeat, while position is not
not-found ,- Append position to matchPositions.
- Set position to
StringIndexOf (string, searchString, position + advanceBy).
- Let endOfLastMatch be 0.
- Let result be the empty String.
- For each element p of matchPositions, do
- Let preserved be the
substring of string from endOfLastMatch to p. - If functionalReplace is
true , then - Else,
Assert : replaceValueis a String .- Let captures be a new empty
List . - Let replacement be !
GetSubstitution (searchString, string, p, captures,undefined , replaceValue).
- Set result to the
string-concatenation of result, preserved, and replacement. - Set endOfLastMatch to p + searchLength.
- Let preserved be the
- If endOfLastMatch < the length of string, then
- Set result to the
string-concatenation of result and thesubstring of string from endOfLastMatch.
- Set result to the
- Return result.
22.1.3.21 String.prototype.search ( regexp )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If regexp is neither
undefined nornull , then- Let searcher be ?
GetMethod (regexp,%Symbol.search% ). - If searcher is not
undefined , then- Return ?
Call (searcher, regexp, « O »).
- Return ?
- Let searcher be ?
- Let string be ?
ToString (O). - Let rx be ?
RegExpCreate (regexp,undefined ). - Return ?
Invoke (rx,%Symbol.search% , « string »).
This method is intentionally generic; it does not require that its
22.1.3.22 String.prototype.slice ( start, end )
This method returns a
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let len be the length of S.
- Let intStart be ?
ToIntegerOrInfinity (start). - If intStart = -∞, let from be 0.
- Else if intStart < 0, let from be
max (len + intStart, 0). - Else, let from be
min (intStart, len). - If end is
undefined , let intEnd be len; else let intEnd be ?ToIntegerOrInfinity (end). - If intEnd = -∞, let to be 0.
- Else if intEnd < 0, let to be
max (len + intEnd, 0). - Else, let to be
min (intEnd, len). - If from ≥ to, return the empty String.
- Return the
substring of S from from to to.
This method is intentionally generic; it does not require that its
22.1.3.23 String.prototype.split ( separator, limit )
This method returns an Array into which substrings of the result of converting this object to a String have been stored. The substrings are determined by searching from left to right for occurrences of separator; these occurrences are not part of any String in the returned array, but serve to divide up the String value. The value of separator may be a String of any length or it may be an object, such as a RegExp, that has a
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - If separator is neither
undefined nornull , then- Let splitter be ?
GetMethod (separator,%Symbol.split% ). - If splitter is not
undefined , then- Return ?
Call (splitter, separator, « O, limit »).
- Return ?
- Let splitter be ?
- Let S be ?
ToString (O). - If limit is
undefined , let lim be 232 - 1; else let lim beℝ (?ToUint32 (limit)). - Let R be ?
ToString (separator). - If lim = 0, then
- Return
CreateArrayFromList (« »).
- Return
- If separator is
undefined , then- Return
CreateArrayFromList (« S »).
- Return
- Let separatorLength be the length of R.
- If separatorLength = 0, then
- Let strLen be the length of S.
- Let outLen be the result of
clamping lim between 0 and strLen. - Let head be the
substring of S from 0 to outLen. - Let codeUnits be a
List consisting of the sequence of code units that are the elements of head. - Return
CreateArrayFromList (codeUnits).
- If S is the empty String, return
CreateArrayFromList (« S »). - Let substrings be a new empty
List . - Let i be 0.
- Let j be
StringIndexOf (S, R, 0). - Repeat, while j is not
not-found ,- Let T be the
substring of S from i to j. - Append T to substrings.
- If the number of elements in substrings is lim, return
CreateArrayFromList (substrings). - Set i to j + separatorLength.
- Set j to
StringIndexOf (S, R, i).
- Let T be the
- Let T be the
substring of S from i. - Append T to substrings.
- Return
CreateArrayFromList (substrings).
The value of separator may be an empty String. In this case, separator does not match the empty
If the
If separator is
This method is intentionally generic; it does not require that its
22.1.3.24 String.prototype.startsWith ( searchString [ , position ] )
This method performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let isRegExp be ?
IsRegExp (searchString). - If isRegExp is
true , throw aTypeError exception. - Let searchStr be ?
ToString (searchString). - Let len be the length of S.
- If position is
undefined , let pos be 0; else let pos be ?ToIntegerOrInfinity (position). - Let start be the result of
clamping pos between 0 and len. - Let searchLength be the length of searchStr.
- If searchLength = 0, return
true . - Let end be start + searchLength.
- If end > len, return
false . - Let substring be the
substring of S from start to end. - If substring is searchStr, return
true . - Return
false .
This method returns
Throwing an exception if the first argument is a RegExp is specified in order to allow future editions to define extensions that allow such argument values.
This method is intentionally generic; it does not require that its
22.1.3.25 String.prototype.substring ( start, end )
This method returns a
If either argument is
If start is strictly greater than end, they are swapped.
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let len be the length of S.
- Let intStart be ?
ToIntegerOrInfinity (start). - If end is
undefined , let intEnd be len; else let intEnd be ?ToIntegerOrInfinity (end). - Let finalStart be the result of
clamping intStart between 0 and len. - Let finalEnd be the result of
clamping intEnd between 0 and len. - Let from be
min (finalStart, finalEnd). - Let to be
max (finalStart, finalEnd). - Return the
substring of S from from to to.
This method is intentionally generic; it does not require that its
22.1.3.26 String.prototype.toLocaleLowerCase ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It works exactly the same as toLowerCase except that it is intended to yield a locale-sensitive result corresponding with conventions of the
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
This method is intentionally generic; it does not require that its
22.1.3.27 String.prototype.toLocaleUpperCase ( [ reserved1 [ , reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It works exactly the same as toUpperCase except that it is intended to yield a locale-sensitive result corresponding with conventions of the
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
This method is intentionally generic; it does not require that its
22.1.3.28 String.prototype.toLowerCase ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let sText be
StringToCodePoints (S). - Let lowerText be toLowercase(sText), according to the Unicode Default Case Conversion algorithm.
- Let L be
CodePointsToString (lowerText). - Return L.
The result must be derived according to the locale-insensitive case mappings in the Unicode Character Database (this explicitly includes not only the file UnicodeData.txt, but also all locale-insensitive mappings in the file SpecialCasing.txt that accompanies it).
The case mapping of some code points may produce multiple code points. In this case the result String may not be the same length as the source String. Because both toUpperCase and toLowerCase have context-sensitive behaviour, the methods are not symmetrical. In other words, s.toUpperCase().toLowerCase() is not necessarily equal to s.toLowerCase().
This method is intentionally generic; it does not require that its
22.1.3.29 String.prototype.toString ( )
This method performs the following steps when called:
- Return ?
ThisStringValue (this value).
For a String object, this method happens to return the same thing as the valueOf method.
22.1.3.30 String.prototype.toUpperCase ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It behaves in exactly the same way as String.prototype.toLowerCase, except that the String is mapped using the toUppercase algorithm of the Unicode Default Case Conversion.
This method is intentionally generic; it does not require that its
22.1.3.31 String.prototype.toWellFormed ( )
This method returns a String representation of this object with all
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let S be ?
ToString (O). - Let strLen be the length of S.
- Let k be 0.
- Let result be the empty String.
- Repeat, while k < strLen,
- Let cp be
CodePointAt (S, k). - If cp.[[IsUnpairedSurrogate]] is
true , then- Set result to the
string-concatenation of result and 0xFFFD (REPLACEMENT CHARACTER).
- Set result to the
- Else,
- Set result to the
string-concatenation of result andUTF16EncodeCodePoint (cp.[[CodePoint]]).
- Set result to the
- Set k to k + cp.[[CodeUnitCount]].
- Let cp be
- Return result.
22.1.3.32 String.prototype.trim ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It performs the following steps when called:
- Let S be the
this value. - Return ?
TrimString (S,start+end ).
This method is intentionally generic; it does not require that its
22.1.3.32.1 TrimString ( string, where )
The abstract operation TrimString takes arguments string (an
- Let str be ?
RequireObjectCoercible (string). - Let S be ?
ToString (str). - If where is
start , then- Let T be the String value that is a copy of S with leading white space removed.
- Else if where is
end , then- Let T be the String value that is a copy of S with trailing white space removed.
- Else,
Assert : where isstart+end .- Let T be the String value that is a copy of S with both leading and trailing white space removed.
- Return T.
The definition of white space is the union of
22.1.3.33 String.prototype.trimEnd ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It performs the following steps when called:
- Let S be the
this value. - Return ?
TrimString (S,end ).
This method is intentionally generic; it does not require that its
22.1.3.34 String.prototype.trimStart ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It performs the following steps when called:
- Let S be the
this value. - Return ?
TrimString (S,start ).
This method is intentionally generic; it does not require that its
22.1.3.35 String.prototype.valueOf ( )
This method performs the following steps when called:
- Return ?
ThisStringValue (this value).
22.1.3.35.1 ThisStringValue ( value )
The abstract operation ThisStringValue takes argument value (an
- If value
is a String , return value. - If value
is an Object and value has a [[StringData]] internal slot, then- Let s be value.[[StringData]].
Assert : sis a String .- Return s.
- Throw a
TypeError exception.
22.1.3.36 String.prototype [ %Symbol.iterator% ] ( )
This method returns an
It performs the following steps when called:
- Let O be ?
RequireObjectCoercible (this value). - Let s be ?
ToString (O). - Let closure be a new
Abstract Closure with no parameters that captures s and performs the following steps when called:- Let len be the length of s.
- Let position be 0.
- Repeat, while position < len,
- Let cp be
CodePointAt (s, position). - Let nextIndex be position + cp.[[CodeUnitCount]].
- Let resultString be the
substring of s from position to nextIndex. - Set position to nextIndex.
- Perform ?
GeneratorYield (CreateIteratorResultObject (resultString,false )).
- Let cp be
- Return
undefined .
- Return
CreateIteratorFromClosure (closure,"%StringIteratorPrototype%" ,%StringIteratorPrototype% ).
The value of the
22.1.4 Properties of String Instances
String instances are
String instances have a
22.1.4.1 length
The number of elements in the String value represented by this String object.
Once a String object is initialized, this property is unchanging. It has the attributes { [[Writable]]:
22.1.5 String Iterator Objects
A String Iterator is an object that represents a specific iteration over some specific String instance object. There is not a named
22.1.5.1 The %StringIteratorPrototype% Object
The %StringIteratorPrototype% object:
- has properties that are inherited by all
String Iterator objects . - is an
ordinary object . - has a [[Prototype]] internal slot whose value is
%Iterator.prototype% . - has the following properties:
22.1.5.1.1 %StringIteratorPrototype%.next ( )
- Return ?
GeneratorResume (this value,empty ,"%StringIteratorPrototype%" ).
22.1.5.1.2 %StringIteratorPrototype% [ %Symbol.toStringTag% ]
The initial value of the
This property has the attributes { [[Writable]]:
22.2 RegExp (Regular Expression) Objects
A RegExp object contains a regular expression and the associated flags.
The form and functionality of regular expressions is modelled after the regular expression facility in the Perl 5 programming language.
22.2.1 Patterns
The RegExp
Syntax
Each \u u u \u
The first two lines here are equivalent to CharacterClass.
A number of productions in this section are given alternative definitions in section
22.2.1.1 Static Semantics: Early Errors
This section is amended in
-
It is a Syntax Error if
CountLeftCapturingParensWithin (Pattern ) ≥ 232 - 1. -
It is a Syntax Error if
Pattern contains two distinctGroupSpecifier s x and y such that theCapturingGroupName of x is theCapturingGroupName of y and such thatMightBothParticipate (x, y) istrue .
-
It is a Syntax Error if the MV of the first
DecimalDigits is strictly greater than the MV of the secondDecimalDigits .
-
It is a Syntax Error if the
source text matched by RegularExpressionModifiers contains the same code point more than once.
-
It is a Syntax Error if the
source text matched by the firstRegularExpressionModifiers and thesource text matched by the secondRegularExpressionModifiers are both empty. -
It is a Syntax Error if the
source text matched by the firstRegularExpressionModifiers contains the same code point more than once. -
It is a Syntax Error if the
source text matched by the secondRegularExpressionModifiers contains the same code point more than once. -
It is a Syntax Error if any code point in the
source text matched by the firstRegularExpressionModifiers is also contained in thesource text matched by the secondRegularExpressionModifiers .
-
It is a Syntax Error if
GroupSpecifiersThatMatch (GroupName ) is empty.
-
It is a Syntax Error if the
CapturingGroupNumber ofDecimalEscape is strictly greater thanCountLeftCapturingParensWithin (thePattern containingAtomEscape ).
-
It is a Syntax Error if
IsCharacterClass of the firstClassAtom istrue orIsCharacterClass of the secondClassAtom istrue . -
It is a Syntax Error if
IsCharacterClass of the firstClassAtom isfalse ,IsCharacterClass of the secondClassAtom isfalse , and theCharacterValue of the firstClassAtom is strictly greater than theCharacterValue of the secondClassAtom .
-
It is a Syntax Error if
IsCharacterClass ofClassAtomNoDash istrue orIsCharacterClass ofClassAtom istrue . -
It is a Syntax Error if
IsCharacterClass ofClassAtomNoDash isfalse ,IsCharacterClass ofClassAtom isfalse , and theCharacterValue ofClassAtomNoDash is strictly greater than theCharacterValue ofClassAtom .
-
It is a Syntax Error if the
CharacterValue ofRegExpUnicodeEscapeSequence is not the numeric value of some code point matched by theIdentifierStartChar lexical grammar production.
-
It is a Syntax Error if the
RegExpIdentifierCodePoint ofRegExpIdentifierStart is not matched by theUnicodeIDStart lexical grammar production.
-
It is a Syntax Error if the
CharacterValue ofRegExpUnicodeEscapeSequence is not the numeric value of some code point matched by theIdentifierPartChar lexical grammar production.
-
It is a Syntax Error if the
RegExpIdentifierCodePoint ofRegExpIdentifierPart is not matched by theUnicodeIDContinue lexical grammar production.
-
It is a Syntax Error if the
source text matched by UnicodePropertyName is not a Unicodeproperty name or property alias listed in the “Property name and aliases” column ofTable 69 . -
It is a Syntax Error if the
source text matched by UnicodePropertyValue is not a property value or property value alias for the Unicode property or property alias given by thesource text matched by UnicodePropertyName listed inPropertyValueAliases.txt.
-
It is a Syntax Error if the
source text matched by LoneUnicodePropertyNameOrValue is not a Unicode property value or property value alias for the General_Category (gc) property listed inPropertyValueAliases.txt, nor a binary property or binary property alias listed in the “Property name and aliases” column ofTable 70 , nor a binary property of strings listed in the “Property name ” column ofTable 71 . -
It is a Syntax Error if the enclosing
Pattern does not have a [UnicodeSetsMode] parameter and thesource text matched by LoneUnicodePropertyNameOrValue is a binary property of strings listed in the “Property name ” column ofTable 71 .
-
It is a Syntax Error if
MayContainStrings of theUnicodePropertyValueExpression istrue .
-
It is a Syntax Error if
MayContainStrings of theClassContents istrue .
-
It is a Syntax Error if
MayContainStrings of theClassContents istrue .
-
It is a Syntax Error if the
CharacterValue of the firstClassSetCharacter is strictly greater than theCharacterValue of the secondClassSetCharacter .
22.2.1.2 Static Semantics: CountLeftCapturingParensWithin ( node )
The abstract operation CountLeftCapturingParensWithin takes argument node (a ( pattern character that is matched by the ( terminal of the
This section is amended in
It performs the following steps when called:
Assert : node is an instance of a production inthe RegExp Pattern grammar .- Return the number of
Atom :: ( GroupSpecifier opt Disjunction ) Parse Nodes contained within node.
22.2.1.3 Static Semantics: CountLeftCapturingParensBefore ( node )
The abstract operation CountLeftCapturingParensBefore takes argument node (a
This section is amended in
It performs the following steps when called:
Assert : node is an instance of a production inthe RegExp Pattern grammar .- Let pattern be the
Pattern containing node. - Return the number of
Atom :: ( GroupSpecifier opt Disjunction ) Parse Nodes contained within pattern that either occur before node or contain node.
22.2.1.4 Static Semantics: MightBothParticipate ( x, y )
The abstract operation MightBothParticipate takes arguments x (a
Assert : x and y have the same enclosingPattern .- If the enclosing
Pattern contains aDisjunction :: Alternative | Disjunction Parse Node such that either x is contained within theAlternative and y is contained within the derivedDisjunction , or x is contained within the derivedDisjunction and y is contained within theAlternative , returnfalse . - Return
true .
22.2.1.5 Static Semantics: CapturingGroupNumber
The
This section is amended in
It is defined piecewise over the following productions:
- Return the MV of
NonZeroDigit .
- Let n be the number of code points in
DecimalDigits . - Return (the MV of
NonZeroDigit × 10n plus the MV ofDecimalDigits ).
The definitions of “the MV of
22.2.1.6 Static Semantics: IsCharacterClass
The
This section is amended in
It is defined piecewise over the following productions:
- Return
false .
- Return
true .
22.2.1.7 Static Semantics: CharacterValue
The
This section is amended in
It is defined piecewise over the following productions:
- Return the numeric value of U+002D (HYPHEN-MINUS).
- Let ch be the code point matched by
SourceCharacter . - Return the numeric value of ch.
- Return the numeric value of U+0008 (BACKSPACE).
- Return the numeric value of U+002D (HYPHEN-MINUS).
- Return the numeric value according to
Table 67 .
| ControlEscape | Numeric Value | Code Point | Unicode Name | Symbol |
|---|---|---|---|---|
t
|
9 |
U+0009
|
CHARACTER TABULATION | <HT> |
n
|
10 |
U+000A
|
LINE FEED (LF) | <LF> |
v
|
11 |
U+000B
|
LINE TABULATION | <VT> |
f
|
12 |
U+000C
|
FORM FEED (FF) | <FF> |
r
|
13 |
U+000D
|
CARRIAGE RETURN (CR) | <CR> |
- Let ch be the code point matched by
AsciiLetter . - Let i be the numeric value of ch.
- Return the remainder of dividing i by 32.
- Return the numeric value of U+0000 (NULL).
\0 represents the <NUL> character and cannot be followed by a decimal digit.
- Return the MV of
HexEscapeSequence .
- Let lead be the
CharacterValue ofHexLeadSurrogate . - Let trail be the
CharacterValue ofHexTrailSurrogate . - Let cp be
UTF16SurrogatePairToCodePoint (lead, trail). - Return the numeric value of cp.
- Return the MV of
Hex4Digits .
- Return the MV of
CodePoint .
- Return the MV of
Hex4Digits .
- Let ch be the code point matched by
IdentityEscape . - Return the numeric value of ch.
- Let ch be the code point matched by
SourceCharacter . - Return the numeric value of ch.
- Let ch be the code point matched by
ClassSetReservedPunctuator . - Return the numeric value of ch.
- Return the numeric value of U+0008 (BACKSPACE).
22.2.1.8 Static Semantics: MayContainStrings
The
- Return
false .
- If the
source text matched by LoneUnicodePropertyNameOrValue is a binary property of strings listed in the “Property name ” column ofTable 71 , returntrue . - Return
false .
- If the
ClassUnion is present, returnMayContainStrings of theClassUnion . - Return
false .
- If
MayContainStrings of theClassSetOperand istrue , returntrue . - If
ClassUnion is present, returnMayContainStrings of theClassUnion . - Return
false .
- If
MayContainStrings of the firstClassSetOperand isfalse , returnfalse . - If
MayContainStrings of the secondClassSetOperand isfalse , returnfalse . - Return
true .
- If
MayContainStrings of theClassIntersection isfalse , returnfalse . - If
MayContainStrings of theClassSetOperand isfalse , returnfalse . - Return
true .
- Return
MayContainStrings of the firstClassSetOperand .
- Return
MayContainStrings of theClassSubtraction .
- If
MayContainStrings of theClassString istrue , returntrue . - Return
MayContainStrings of theClassStringDisjunctionContents .
- Return
true .
- Return
MayContainStrings of theNonEmptyClassString .
- If
NonEmptyClassString is present, returntrue . - Return
false .
22.2.1.9 Static Semantics: GroupSpecifiersThatMatch ( thisGroupName )
The abstract operation GroupSpecifiersThatMatch takes argument thisGroupName (a
- Let name be the
CapturingGroupName of thisGroupName. - Let pattern be the
Pattern containing thisGroupName. - Let result be a new empty
List . - For each
GroupSpecifier gs that pattern contains, do- If the
CapturingGroupName of gs is name, then- Append gs to result.
- If the
- Return result.
22.2.1.10 Static Semantics: CapturingGroupName
The
- Let idTextUnescaped be the
RegExpIdentifierCodePoints ofRegExpIdentifierName . - Return
CodePointsToString (idTextUnescaped).
22.2.1.11 Static Semantics: RegExpIdentifierCodePoints
The
- Let cp be the
RegExpIdentifierCodePoint ofRegExpIdentifierStart . - Return « cp ».
- Let cps be the
RegExpIdentifierCodePoints of the derivedRegExpIdentifierName . - Let cp be the
RegExpIdentifierCodePoint ofRegExpIdentifierPart . - Return the
list-concatenation of cps and « cp ».
22.2.1.12 Static Semantics: RegExpIdentifierCodePoint
The
- Return the code point matched by
IdentifierStartChar .
- Return the code point matched by
IdentifierPartChar .
- Return the code point whose numeric value is the
CharacterValue ofRegExpUnicodeEscapeSequence .
- Let lead be the code unit whose numeric value is the numeric value of the code point matched by
UnicodeLeadSurrogate . - Let trail be the code unit whose numeric value is the numeric value of the code point matched by
UnicodeTrailSurrogate . - Return
UTF16SurrogatePairToCodePoint (lead, trail).
22.2.2 Pattern Semantics
A regular expression pattern is converted into an
A u nor a v. Otherwise, it is a Unicode pattern. A BMP pattern matches against a String interpreted as consisting of a sequence of 16-bit values that are Unicode code points in the range of the Basic Multilingual Plane. A Unicode pattern matches against a String interpreted as consisting of Unicode code points encoded using UTF-16. In the context of describing the behaviour of a BMP pattern “character” means a single 16-bit Unicode BMP code point. In the context of describing the behaviour of a Unicode pattern “character” means a UTF-16 encoded code point (
The syntax and semantics of
For example, consider a pattern expressed in source text as the single non-BMP character U+1D11E (MUSICAL SYMBOL G CLEF). Interpreted as a Unicode pattern, it would be a single element (character)
Patterns are passed to the RegExp
An implementation may not actually perform such translations to or from UTF-16, but the semantics of this specification requires that the result of pattern matching be as if such translations were performed.
22.2.2.1 Notation
The descriptions below use the following internal data structures:
-
A CharSetElement is one of the two following entities:
-
If rer.[[UnicodeSets]] is
false , then a CharSetElement is a character in the sense of the Pattern Semantics above. -
If rer.[[UnicodeSets]] is
true , then a CharSetElement is a sequence whose elements are characters in the sense of the Pattern Semantics above. This includes the empty sequence, sequences of one character, and sequences of more than one character. For convenience, when working with CharSetElements of this kind, an individual character is treated interchangeably with a sequence of one character.
-
If rer.[[UnicodeSets]] is
- A CharSet is a mathematical set of CharSetElements.
-
A CaptureRange is a
Record { [[StartIndex]], [[EndIndex]] } that represents the range of characters included in a capture, where [[StartIndex]] is aninteger representing the start index (inclusive) of the range within Input, and [[EndIndex]] is aninteger representing the end index (exclusive) of the range within Input. For anyCaptureRange , these indices must satisfy the invariant that [[StartIndex]] ≤ [[EndIndex]]. -
A MatchState is a
Record { [[Input]], [[EndIndex]], [[Captures]] } where [[Input]] is aList of characters representing the String being matched, [[EndIndex]] is aninteger , and [[Captures]] is aList of values, one for eachleft-capturing parenthesis in the pattern.MatchStates are used to represent partial match states in the regular expression matching algorithms. The [[EndIndex]] is one plus the index of the last input character matched so far by the pattern, while [[Captures]] holds the results of capturing parentheses. The nth element of [[Captures]] is either aCaptureRange representing the range of characters captured by the nth set of capturing parentheses, orundefined if the nth set of capturing parentheses hasn't been reached yet. Due to backtracking, manyMatchStates may be in use at any time during the matching process. -
A MatcherContinuation is an
Abstract Closure that takes oneMatchState argument and returns either aMatchState orfailure . TheMatcherContinuation attempts to match the remaining portion (specified by the closure's captured values) of the pattern against Input, starting at the intermediate state given by itsMatchState argument. If the match succeeds, theMatcherContinuation returns the finalMatchState that it reached; if the match fails, theMatcherContinuation returnsfailure . -
A Matcher is an
Abstract Closure that takes two arguments—aMatchState and aMatcherContinuation —and returns either aMatchState orfailure . AMatcher attempts to match a middle subpattern (specified by the closure's captured values) of the pattern against theMatchState 's [[Input]], starting at the intermediate state given by itsMatchState argument. TheMatcherContinuation argument should be a closure that matches the rest of the pattern. After matching the subpattern of a pattern to obtain a newMatchState , theMatcher then callsMatcherContinuation on that newMatchState to test if the rest of the pattern can match as well. If it can, theMatcher returns theMatchState returned byMatcherContinuation ; if not, theMatcher may try different choices at its choice points, repeatedly callingMatcherContinuation until it either succeeds or all possibilities have been exhausted.
22.2.2.1.1 RegExp Records
A RegExp Record is a
It has the following fields:
| Field Name | Value | Meaning |
|---|---|---|
| [[IgnoreCase]] | a Boolean | indicates whether |
| [[Multiline]] | a Boolean | indicates whether |
| [[DotAll]] | a Boolean | indicates whether |
| [[Unicode]] | a Boolean | indicates whether |
| [[UnicodeSets]] | a Boolean | indicates whether |
| [[CapturingGroupsCount]] | a non-negative |
the number of |
22.2.2.2 Runtime Semantics: CompilePattern
The
- Let m be
CompileSubpattern ofDisjunction with arguments rer andforward . - Return a new
Abstract Closure with parameters (Input, index) that captures rer and m and performs the following steps when called:Assert : Input is aList of characters.Assert : 0 ≤ index ≤ the number of elements in Input.- Let c be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert : y is aMatchState .- Return y.
- Let cap be a
List of rer.[[CapturingGroupsCount]]undefined values, indexed 1 through rer.[[CapturingGroupsCount]]. - Let x be the
MatchState { [[Input]]: Input, [[EndIndex]]: index, [[Captures]]: cap }. - Return m(x, c).
A Pattern compiles to an
22.2.2.3 Runtime Semantics: CompileSubpattern
The
This section is amended in
It is defined piecewise over the following productions:
- Let m1 be
CompileSubpattern ofAlternative with arguments rer and direction. - Let m2 be
CompileSubpattern ofDisjunction with arguments rer and direction. - Return
MatchTwoAlternatives (m1, m2).
The | regular expression operator separates two alternatives. The pattern first tries to match the left | produce
/a|ab/.exec("abc")returns the result
/((a)|(ab))((c)|(bc))/.exec("abc")returns the array
["abc", "a", "a", undefined, "bc", undefined, "bc"]and not
["abc", "ab", undefined, "ab", "c", "c", undefined]The order in which the two alternatives are tried is independent of the value of direction.
- Return
EmptyMatcher ().
- Let m1 be
CompileSubpattern ofAlternative with arguments rer and direction. - Let m2 be
CompileSubpattern ofTerm with arguments rer and direction. - Return
MatchSequence (m1, m2, direction).
Consecutive
- Return
CompileAssertion ofAssertion with argument rer.
The resulting
- Return
CompileAtom ofAtom with arguments rer and direction.
- Let m be
CompileAtom ofAtom with arguments rer and direction. - Let q be
CompileQuantifier ofQuantifier . Assert : q.[[Min]] ≤ q.[[Max]].- Let parenIndex be
CountLeftCapturingParensBefore (Term ). - Let parenCount be
CountLeftCapturingParensWithin (Atom ). - Return a new
Matcher with parameters (x, c) that captures m, q, parenIndex, and parenCount and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Return
RepeatMatcher (m, q.[[Min]], q.[[Max]], q.[[Greedy]], x, c, parenIndex, parenCount).
22.2.2.3.1 RepeatMatcher ( m, min, max, greedy, x, c, parenIndex, parenCount )
The abstract operation RepeatMatcher takes arguments m (a
- If max = 0, return c(x).
- Let d be a new
MatcherContinuation with parameters (y) that captures m, min, max, greedy, x, c, parenIndex, and parenCount and performs the following steps when called:Assert : y is aMatchState .- If min = 0 and y.[[EndIndex]] = x.[[EndIndex]], return
failure . - If min = 0, let min2 be 0; otherwise let min2 be min - 1.
- If max = +∞, let max2 be +∞; otherwise let max2 be max - 1.
- Return
RepeatMatcher (m, min2, max2, greedy, y, c, parenIndex, parenCount).
- Let cap be a copy of x.[[Captures]].
- For each
integer k in theinclusive interval from parenIndex + 1 to parenIndex + parenCount, set cap[k] toundefined . - Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- Let xr be the
MatchState { [[Input]]: Input, [[EndIndex]]: e, [[Captures]]: cap }. - If min ≠ 0, return m(xr, d).
- If greedy is
false , then- Let z be c(x).
- If z is not
failure , return z. - Return m(xr, d).
- Let z be m(xr, d).
- If z is not
failure , return z. - Return c(x).
An
If the
Compare
/a[a-z]{2,4}/.exec("abcdefghi")which returns
/a[a-z]{2,4}?/.exec("abcdefghi")which returns
Consider also
/(aa|aabaac|ba|b|c)*/.exec("aabaac")which, by the choice point ordering above, returns the array
["aaba", "ba"]and not any of:
["aabaac", "aabaac"]
["aabaac", "c"]The above ordering of choice points can be used to write a regular expression that calculates the greatest common divisor of two numbers (represented in unary notation). The following example calculates the gcd of 10 and 15:
"aaaaaaaaaa,aaaaaaaaaaaaaaa".replace(/^(a+)\1*,\1+$/, "$1")which returns the gcd in unary notation
Step
/(z)((a+)?(b+)?(c))*/.exec("zaacbbbcac")which returns the array
["zaacbbbcac", "z", "ac", "a", undefined, "c"]and not
["zaacbbbcac", "z", "ac", "a", "bbb", "c"]because each iteration of the outermost * clears all captured Strings contained in the quantified
Step
/(a*)*/.exec("b")or the slightly more complicated:
/(a*)b\1+/.exec("baaaac")which returns the array
["b", ""]22.2.2.3.2 EmptyMatcher ( )
The abstract operation EmptyMatcher takes no arguments and returns a
- Return a new
Matcher with parameters (x, c) that captures nothing and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Return c(x).
22.2.2.3.3 MatchTwoAlternatives ( m1, m2 )
The abstract operation MatchTwoAlternatives takes arguments m1 (a
- Return a new
Matcher with parameters (x, c) that captures m1 and m2 and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let r be m1(x, c).
- If r is not
failure , return r. - Return m2(x, c).
22.2.2.3.4 MatchSequence ( m1, m2, direction )
The abstract operation MatchSequence takes arguments m1 (a
- If direction is
forward , then- Return a new
Matcher with parameters (x, c) that captures m1 and m2 and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures c and m2 and performs the following steps when called:Assert : y is aMatchState .- Return m2(y, c).
- Return m1(x, d).
- Return a new
- Else,
Assert : direction isbackward .- Return a new
Matcher with parameters (x, c) that captures m1 and m2 and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures c and m1 and performs the following steps when called:Assert : y is aMatchState .- Return m1(y, c).
- Return m2(x, d).
22.2.2.4 Runtime Semantics: CompileAssertion
The
This section is amended in
It is defined piecewise over the following productions:
- Return a new
Matcher with parameters (x, c) that captures rer and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- If e = 0, or if rer.[[Multiline]] is
true and the character Input[e - 1] is matched byLineTerminator , then- Return c(x).
- Return
failure .
Even when the y flag is used with a pattern, ^ always matches only at the beginning of Input, or (if rer.[[Multiline]] is
- Return a new
Matcher with parameters (x, c) that captures rer and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- Let InputLength be the number of elements in Input.
- If e = InputLength, or if rer.[[Multiline]] is
true and the character Input[e] is matched byLineTerminator , then- Return c(x).
- Return
failure .
- Return a new
Matcher with parameters (x, c) that captures rer and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- Let a be
IsWordChar (rer, Input, e - 1). - Let b be
IsWordChar (rer, Input, e). - If a is
true and b isfalse , or if a isfalse and b istrue , return c(x). - Return
failure .
- Return a new
Matcher with parameters (x, c) that captures rer and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- Let a be
IsWordChar (rer, Input, e - 1). - Let b be
IsWordChar (rer, Input, e). - If a is
true and b istrue , or if a isfalse and b isfalse , return c(x). - Return
failure .
- Let m be
CompileSubpattern ofDisjunction with arguments rer andforward . - Return a new
Matcher with parameters (x, c) that captures m and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert : y is aMatchState .- Return y.
- Let r be m(x, d).
- If r is
failure , returnfailure . Assert : r is aMatchState .- Let cap be r.[[Captures]].
- Let Input be x.[[Input]].
- Let xe be x.[[EndIndex]].
- Let z be the
MatchState { [[Input]]: Input, [[EndIndex]]: xe, [[Captures]]: cap }. - Return c(z).
The form (?= ) specifies a zero-width positive lookahead. In order for it to succeed, the pattern inside (?= form (this unusual behaviour is inherited from Perl). This only matters when the
For example,
/(?=(a+))/.exec("baaabac")matches the empty String immediately after the first b and therefore returns the array:
["", "aaa"]To illustrate the lack of backtracking into the lookahead, consider:
/(?=(a+))a*b\1/.exec("baaabac")This expression returns
["aba", "a"]and not:
["aaaba", "a"]- Let m be
CompileSubpattern ofDisjunction with arguments rer andforward . - Return a new
Matcher with parameters (x, c) that captures m and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert : y is aMatchState .- Return y.
- Let r be m(x, d).
- If r is not
failure , returnfailure . - Return c(x).
The form (?! ) specifies a zero-width negative lookahead. In order for it to succeed, the pattern inside
/(.*?)a(?!(a+)b\2c)\2(.*)/.exec("baaabaac")looks for an a not immediately followed by some positive number n of a's, a b, another n a's (specified by the first \2) and a c. The second \2 is outside the negative lookahead, so it matches against
["baaabaac", "ba", undefined, "abaac"]- Let m be
CompileSubpattern ofDisjunction with arguments rer andbackward . - Return a new
Matcher with parameters (x, c) that captures m and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert : y is aMatchState .- Return y.
- Let r be m(x, d).
- If r is
failure , returnfailure . Assert : r is aMatchState .- Let cap be r.[[Captures]].
- Let Input be x.[[Input]].
- Let xe be x.[[EndIndex]].
- Let z be the
MatchState { [[Input]]: Input, [[EndIndex]]: xe, [[Captures]]: cap }. - Return c(z).
- Let m be
CompileSubpattern ofDisjunction with arguments rer andbackward . - Return a new
Matcher with parameters (x, c) that captures m and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert : y is aMatchState .- Return y.
- Let r be m(x, d).
- If r is not
failure , returnfailure . - Return c(x).
22.2.2.4.1 IsWordChar ( rer, Input, e )
The abstract operation IsWordChar takes arguments rer (a
- Let InputLength be the number of elements in Input.
- If e = -1 or e = InputLength, return
false . - Let c be the character Input[e].
- If
WordCharacters (rer) contains c, returntrue . - Return
false .
22.2.2.5 Runtime Semantics: CompileQuantifier
The
- Let qp be
CompileQuantifierPrefix ofQuantifierPrefix . - Return the
Record { [[Min]]: qp.[[Min]], [[Max]]: qp.[[Max]], [[Greedy]]:true }.
- Let qp be
CompileQuantifierPrefix ofQuantifierPrefix . - Return the
Record { [[Min]]: qp.[[Min]], [[Max]]: qp.[[Max]], [[Greedy]]:false }.
22.2.2.6 Runtime Semantics: CompileQuantifierPrefix
The
- Return the
Record { [[Min]]: 0, [[Max]]: +∞ }.
- Return the
Record { [[Min]]: 1, [[Max]]: +∞ }.
- Return the
Record { [[Min]]: 0, [[Max]]: 1 }.
- Let i be the MV of
DecimalDigits (see12.9.3 ). - Return the
Record { [[Min]]: i, [[Max]]: i }.
- Let i be the MV of
DecimalDigits . - Return the
Record { [[Min]]: i, [[Max]]: +∞ }.
- Let i be the MV of the first
DecimalDigits . - Let j be the MV of the second
DecimalDigits . - Return the
Record { [[Min]]: i, [[Max]]: j }.
22.2.2.7 Runtime Semantics: CompileAtom
The
This section is amended in
It is defined piecewise over the following productions:
- Let ch be the character matched by
PatternCharacter . - Let A be a one-element
CharSet containing the character ch. - Return
CharacterSetMatcher (rer, A,false , direction).
- Let A be
AllCharacters (rer). - If rer.[[DotAll]] is not
true , then- Remove from A all characters corresponding to a code point on the right-hand side of the
LineTerminator production.
- Remove from A all characters corresponding to a code point on the right-hand side of the
- Return
CharacterSetMatcher (rer, A,false , direction).
- Let cc be
CompileCharacterClass ofCharacterClass with argument rer. - Let cs be cc.[[CharSet]].
- If rer.[[UnicodeSets]] is
false , or if everyCharSetElement of cs consists of a single character (including if cs is empty), returnCharacterSetMatcher (rer, cs, cc.[[Invert]], direction). Assert : cc.[[Invert]] isfalse .- Let lm be an empty
List ofMatchers . - For each
CharSetElement s in cs containing more than 1 character, iterating in descending order of length, do- Let cs2 be a one-element
CharSet containing the last code point of s. - Let m2 be
CharacterSetMatcher (rer, cs2,false , direction). - For each code point c1 in s, iterating backwards from its second-to-last code point, do
- Let cs1 be a one-element
CharSet containing c1. - Let m1 be
CharacterSetMatcher (rer, cs1,false , direction). - Set m2 to
MatchSequence (m1, m2, direction).
- Let cs1 be a one-element
- Append m2 to lm.
- Let cs2 be a one-element
- Let singles be the
CharSet containing everyCharSetElement of cs that consists of a single character. - Append
CharacterSetMatcher (rer, singles,false , direction) to lm. - If cs contains the empty sequence of characters, append
EmptyMatcher () to lm. - Let m2 be the last
Matcher in lm. - For each
Matcher m1 of lm, iterating backwards from its second-to-last element, do- Set m2 to
MatchTwoAlternatives (m1, m2).
- Set m2 to
- Return m2.
- Let m be
CompileSubpattern ofDisjunction with arguments rer and direction. - Let parenIndex be
CountLeftCapturingParensBefore (Atom ). - Return a new
Matcher with parameters (x, c) that captures direction, m, and parenIndex and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let d be a new
MatcherContinuation with parameters (y) that captures x, c, direction, and parenIndex and performs the following steps when called:Assert : y is aMatchState .- Let cap be a copy of y.[[Captures]].
- Let Input be x.[[Input]].
- Let xe be x.[[EndIndex]].
- Let ye be y.[[EndIndex]].
- If direction is
forward , thenAssert : xe ≤ ye.- Let r be the
CaptureRange { [[StartIndex]]: xe, [[EndIndex]]: ye }.
- Else,
Assert : direction isbackward .Assert : ye ≤ xe.- Let r be the
CaptureRange { [[StartIndex]]: ye, [[EndIndex]]: xe }.
- Set cap[parenIndex + 1] to r.
- Let z be the
MatchState { [[Input]]: Input, [[EndIndex]]: ye, [[Captures]]: cap }. - Return c(z).
- Return m(x, d).
Parentheses of the form ( ) serve both to group the components of the \ followed by a non-zero decimal number), referenced in a replace String, or returned as part of an array from the regular expression matching (?: ) instead.
- Let addModifiers be the
source text matched by RegularExpressionModifiers . - Let removeModifiers be the empty String.
- Let modifiedRer be
UpdateModifiers (rer,CodePointsToString (addModifiers), removeModifiers). - Return
CompileSubpattern ofDisjunction with arguments modifiedRer and direction.
- Let addModifiers be the
source text matched by the firstRegularExpressionModifiers . - Let removeModifiers be the
source text matched by the secondRegularExpressionModifiers . - Let modifiedRer be
UpdateModifiers (rer,CodePointsToString (addModifiers),CodePointsToString (removeModifiers)). - Return
CompileSubpattern ofDisjunction with arguments modifiedRer and direction.
- Let n be the
CapturingGroupNumber ofDecimalEscape . Assert : n ≤ rer.[[CapturingGroupsCount]].- Return
BackreferenceMatcher (rer, « n », direction).
An escape sequence of the form \ followed by a non-zero decimal number n matches the result of the nth set of capturing parentheses (
- Let cv be the
CharacterValue ofCharacterEscape . - Let ch be the character whose character value is cv.
- Let A be a one-element
CharSet containing the character ch. - Return
CharacterSetMatcher (rer, A,false , direction).
- Let cs be
CompileToCharSet ofCharacterClassEscape with argument rer. - If rer.[[UnicodeSets]] is
false , or if everyCharSetElement of cs consists of a single character (including if cs is empty), returnCharacterSetMatcher (rer, cs,false , direction). - Let lm be an empty
List ofMatchers . - For each
CharSetElement s in cs containing more than 1 character, iterating in descending order of length, do- Let cs2 be a one-element
CharSet containing the last code point of s. - Let m2 be
CharacterSetMatcher (rer, cs2,false , direction). - For each code point c1 in s, iterating backwards from its second-to-last code point, do
- Let cs1 be a one-element
CharSet containing c1. - Let m1 be
CharacterSetMatcher (rer, cs1,false , direction). - Set m2 to
MatchSequence (m1, m2, direction).
- Let cs1 be a one-element
- Append m2 to lm.
- Let cs2 be a one-element
- Let singles be the
CharSet containing everyCharSetElement of cs that consists of a single character. - Append
CharacterSetMatcher (rer, singles,false , direction) to lm. - If cs contains the empty sequence of characters, append
EmptyMatcher () to lm. - Let m2 be the last
Matcher in lm. - For each
Matcher m1 of lm, iterating backwards from its second-to-last element, do- Set m2 to
MatchTwoAlternatives (m1, m2).
- Set m2 to
- Return m2.
- Let matchingGroupSpecifiers be
GroupSpecifiersThatMatch (GroupName ). - Let parenIndices be a new empty
List . - For each
GroupSpecifier groupSpecifier of matchingGroupSpecifiers, do- Let parenIndex be
CountLeftCapturingParensBefore (groupSpecifier). - Append parenIndex to parenIndices.
- Let parenIndex be
- Return
BackreferenceMatcher (rer, parenIndices, direction).
22.2.2.7.1 CharacterSetMatcher ( rer, A, invert, direction )
The abstract operation CharacterSetMatcher takes arguments rer (a
- If rer.[[UnicodeSets]] is
true , thenAssert : invert isfalse .Assert : EveryCharSetElement of A consists of a single character.
- Return a new
Matcher with parameters (x, c) that captures rer, A, invert, and direction and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let e be x.[[EndIndex]].
- If direction is
forward , let f be e + 1. - Else, let f be e - 1.
- Let InputLength be the number of elements in Input.
- If f < 0 or f > InputLength, return
failure . - Let index be
min (e, f). - Let ch be the character Input[index].
- Let cc be
Canonicalize (rer, ch). - If there exists a
CharSetElement in A containing exactly one character a such thatCanonicalize (rer, a) is cc, let found betrue . Otherwise, let found befalse . - If invert is
false and found isfalse , returnfailure . - If invert is
true and found istrue , returnfailure . - Let cap be x.[[Captures]].
- Let y be the
MatchState { [[Input]]: Input, [[EndIndex]]: f, [[Captures]]: cap }. - Return c(y).
22.2.2.7.2 BackreferenceMatcher ( rer, ns, direction )
The abstract operation BackreferenceMatcher takes arguments rer (a
- Return a new
Matcher with parameters (x, c) that captures rer, ns, and direction and performs the following steps when called:Assert : x is aMatchState .Assert : c is aMatcherContinuation .- Let Input be x.[[Input]].
- Let cap be x.[[Captures]].
- Let r be
undefined . - For each
integer n of ns, do- If cap[n] is not
undefined , thenAssert : r isundefined .- Set r to cap[n].
- If cap[n] is not
- If r is
undefined , return c(x). - Let e be x.[[EndIndex]].
- Let rs be r.[[StartIndex]].
- Let re be r.[[EndIndex]].
- Let len be re - rs.
- If direction is
forward , let f be e + len. - Else, let f be e - len.
- Let InputLength be the number of elements in Input.
- If f < 0 or f > InputLength, return
failure . - Let g be
min (e, f). - If there exists an
integer i in theinterval from 0 (inclusive) to len (exclusive) such thatCanonicalize (rer, Input[rs + i]) is notCanonicalize (rer, Input[g + i]), returnfailure . - Let y be the
MatchState { [[Input]]: Input, [[EndIndex]]: f, [[Captures]]: cap }. - Return c(y).
22.2.2.7.3 Canonicalize ( rer, ch )
The abstract operation Canonicalize takes arguments rer (a
- If
HasEitherUnicodeFlag (rer) istrue and rer.[[IgnoreCase]] istrue , then- If the file
CaseFolding.txtof the Unicode Character Database provides a simple or common case folding mapping for ch, return the result of applying that mapping to ch. - Return ch.
- If the file
- If rer.[[IgnoreCase]] is
false , return ch. Assert : ch is a UTF-16 code unit.- Let cp be the code point whose numeric value is the numeric value of ch.
- Let u be toUppercase(« cp »), according to the Unicode Default Case Conversion algorithm.
- Let uStr be
CodePointsToString (u). - If the length of uStr ≠ 1, return ch.
- Let cu be uStr's single code unit element.
- If the numeric value of ch ≥ 128 and the numeric value of cu < 128, return ch.
- Return cu.
In case-insignificant matches when ß (U+00DF LATIN SMALL LETTER SHARP S) to ss or SS. It may however map code points outside the Basic Latin block to code points within it—for example, ſ (U+017F LATIN SMALL LETTER LONG S) case-folds to s (U+0073 LATIN SMALL LETTER S) and K (U+212A KELVIN SIGN) case-folds to k (U+006B LATIN SMALL LETTER K). Strings containing those code points are matched by regular expressions such as /[a-z]/ui.
In case-insignificant matches when Ω (U+2126 OHM SIGN) is mapped by toUppercase to itself but by toCasefold to ω (U+03C9 GREEK SMALL LETTER OMEGA) along with Ω (U+03A9 GREEK CAPITAL LETTER OMEGA), so /[ω]/ui and /[\u03A9]/ui but not by /[ω]/i or /[\u03A9]/i. Also, no code point outside the Basic Latin block is mapped to a code point within it, so strings such as /[a-z]/i.
22.2.2.7.4 UpdateModifiers ( rer, add, remove )
The abstract operation UpdateModifiers takes arguments rer (a
Assert : add and remove have no elements in common.- Let ignoreCase be rer.[[IgnoreCase]].
- Let multiline be rer.[[Multiline]].
- Let dotAll be rer.[[DotAll]].
- Let unicode be rer.[[Unicode]].
- Let unicodeSets be rer.[[UnicodeSets]].
- Let capturingGroupsCount be rer.[[CapturingGroupsCount]].
- If remove contains
"i" , set ignoreCase tofalse . - Else if add contains
"i" , set ignoreCase totrue . - If remove contains
"m" , set multiline tofalse . - Else if add contains
"m" , set multiline totrue . - If remove contains
"s" , set dotAll tofalse . - Else if add contains
"s" , set dotAll totrue . - Return the
RegExp Record { [[IgnoreCase]]: ignoreCase, [[Multiline]]: multiline, [[DotAll]]: dotAll, [[Unicode]]: unicode, [[UnicodeSets]]: unicodeSets, [[CapturingGroupsCount]]: capturingGroupsCount }.
22.2.2.8 Runtime Semantics: CompileCharacterClass
The
- Let A be
CompileToCharSet ofClassContents with argument rer. - Return the
Record { [[CharSet]]: A, [[Invert]]:false }.
- Let A be
CompileToCharSet ofClassContents with argument rer. - If rer.[[UnicodeSets]] is
true , then- Return the
Record { [[CharSet]]:CharacterComplement (rer, A), [[Invert]]:false }.
- Return the
- Return the
Record { [[CharSet]]: A, [[Invert]]:true }.
22.2.2.9 Runtime Semantics: CompileToCharSet
The
This section is amended in
It is defined piecewise over the following productions:
- Return the empty
CharSet .
- Let A be
CompileToCharSet ofClassAtom with argument rer. - Let B be