Introduction
1 Scope
+2 Conformance
1. 2.1 Example Normative Optional Clause Heading
2. 2.2 Example Legacy Clause Heading
3. 2.3 Example Legacy Normative Optional Clause Heading
3 Normative References
+4 Overview
1. 4.1 Web Scripting
2. 4.2 Hosts and Implementations
3. +4.3 ECMAScript Overview
  1. 4.3.1 Objects
  2. 4.3.2 The Strict Variant of ECMAScript
4. +4.4 Terms and Definitions
5. 4.5 Organization of This Specification
+5 Notational Conventions
1. +5.1 Syntactic and Lexical Grammars
2. +5.2 Algorithm Conventions
+6 ECMAScript Data Types and Values
1. +6.1 ECMAScript Language Types
2. +6.2 ECMAScript Specification Types
+7 Abstract Operations
1. +7.1 Type Conversion
2. +7.2 Testing and Comparison Operations
3. +7.3 Operations on Objects
4. +7.4 Operations on Iterator Objects
+8 Syntax-Directed Operations
1. 8.1 RS: Evaluation
2. +8.2 Scope Analysis
3. +8.3 Labels
4. +8.4 Function Name Inference
5. +8.5 Contains
  1. 8.5.1 SS: Contains
  2. 8.5.2 SS: ComputedPropertyContains
6. +8.6 Miscellaneous
+9 Executable Code and Execution Contexts
1. +9.1 Environment Records
  1. +9.1.1 The Environment Record Type Hierarchy
  2. +9.1.2 Environment Record Operations
2. +9.2 PrivateEnvironment Records
  1. +9.2.1 PrivateEnvironment Record Operations
    1. 9.2.1.1 NewPrivateEnvironment ( outerPrivateEnv )
    2. 9.2.1.2 ResolvePrivateIdentifier ( privateEnv, identifier )
3. +9.3 Realms
4. +9.4 Execution Contexts
5. +9.5 Jobs and Host Operations to Enqueue Jobs
6. +9.6 Agents
  1. 9.6.1 AgentSignifier ( )
  2. 9.6.2 AgentCanSuspend ( )
7. 9.7 Agent Clusters
8. 9.8 Forward Progress
9. +9.9 Processing Model of WeakRef and FinalizationRegistry Targets
10. 9.10 ClearKeptObjects ( )
11. 9.11 AddToKeptObjects ( value )
12. 9.12 CleanupFinalizationRegistry ( finalizationRegistry )
13. 9.13 CanBeHeldWeakly ( v )
+10 Ordinary and Exotic Objects Behaviours
1. +10.1 Ordinary Object Internal Methods and Internal Slots
2. +10.2 ECMAScript Function Objects
3. +10.3 Built-in Function Objects
4. +10.4 Built-in Exotic Object Internal Methods and Slots
5. +10.5 Proxy Object Internal Methods and Internal Slots
+11 ECMAScript Language: Source Text
1. +11.1 Source Text
2. +11.2 Types of Source Code
+12 ECMAScript Language: Lexical Grammar
1. 12.1 Unicode Format-Control Characters
2. 12.2 White Space
3. 12.3 Line Terminators
4. 12.4 Comments
5. 12.5 Hashbang Comments
6. 12.6 Tokens
7. +12.7 Names and Keywords
  1. +12.7.1 Identifier Names
  2. 12.7.2 Keywords and Reserved Words
8. 12.8 Punctuators
9. +12.9 Literals
10. +12.10 Automatic Semicolon Insertion
+13 ECMAScript Language: Expressions
1. +13.1 Identifiers
2. +13.2 Primary Expression
3. +13.3 Left-Hand-Side Expressions
4. +13.4 Update Expressions
5. +13.5 Unary Operators
6. +13.6 Exponentiation Operator
  1. 13.6.1 RS: Evaluation
7. +13.7 Multiplicative Operators
  1. 13.7.1 RS: Evaluation
8. +13.8 Additive Operators
  1. +13.8.1 The Addition Operator ( + )
    1. 13.8.1.1 RS: Evaluation
  2. +13.8.2 The Subtraction Operator ( - )
    1. 13.8.2.1 RS: Evaluation
9. +13.9 Bitwise Shift Operators
10. +13.10 Relational Operators
  1. 13.10.1 RS: Evaluation
  2. 13.10.2 InstanceofOperator ( V, target )
11. +13.11 Equality Operators
  1. 13.11.1 RS: Evaluation
12. +13.12 Binary Bitwise Operators
  1. 13.12.1 RS: Evaluation
13. +13.13 Binary Logical Operators
  1. 13.13.1 RS: Evaluation
14. +13.14 Conditional Operator ( ? : )
  1. 13.14.1 RS: Evaluation
15. +13.15 Assignment Operators
16. +13.16 Comma Operator ( , )
  1. 13.16.1 RS: Evaluation
+14 ECMAScript Language: Statements and Declarations
1. +14.1 Statement Semantics
  1. 14.1.1 RS: Evaluation
2. +14.2 Block
3. +14.3 Declarations and the Variable Statement
4. +14.4 Empty Statement
  1. 14.4.1 RS: Evaluation
5. +14.5 Expression Statement
  1. 14.5.1 RS: Evaluation
6. +14.6 The if Statement
  1. 14.6.1 SS: Early Errors
  2. 14.6.2 RS: Evaluation
7. +14.7 Iteration Statements
8. +14.8 The continue Statement
  1. 14.8.1 SS: Early Errors
  2. 14.8.2 RS: Evaluation
9. +14.9 The break Statement
  1. 14.9.1 SS: Early Errors
  2. 14.9.2 RS: Evaluation
10. +14.10 The return Statement
  1. 14.10.1 RS: Evaluation
11. +14.11 The with Statement
  1. 14.11.1 SS: Early Errors
  2. 14.11.2 RS: Evaluation
12. +14.12 The switch Statement
13. +14.13 Labelled Statements
14. +14.14 The throw Statement
  1. 14.14.1 RS: Evaluation
15. +14.15 The try Statement
16. +14.16 The debugger Statement
  1. 14.16.1 RS: Evaluation
+15 ECMAScript Language: Functions and Classes
1. +15.1 Parameter Lists
2. +15.2 Function Definitions
3. +15.3 Arrow Function Definitions
4. +15.4 Method Definitions
5. +15.5 Generator Function Definitions
6. +15.6 Async Generator Function Definitions
7. +15.7 Class Definitions
8. +15.8 Async Function Definitions
9. +15.9 Async Arrow Function Definitions
10. +15.10 Tail Position Calls
+16 ECMAScript Language: Scripts and Modules
1. +16.1 Scripts
2. +16.2 Modules
+17 Error Handling and Language Extensions
1. 17.1 Forbidden Extensions
18 ECMAScript Standard Built-in Objects
+19 The Global Object
1. +19.1 Value Properties of the Global Object
2. +19.2 Function Properties of the Global Object
3. +19.3 Constructor Properties of the Global Object
4. +19.4 Other Properties of the Global Object
+20 Fundamental Objects
1. +20.1 Object Objects
2. +20.2 Function Objects
3. +20.3 Boolean Objects
4. +20.4 Symbol Objects
5. +20.5 Error Objects
+21 Numbers and Dates
1. +21.1 Number Objects
2. +21.2 BigInt Objects
3. +21.3 The Math Object
  1. +21.3.1 Value Properties of the Math Object
  2. +21.3.2 Function Properties of the Math Object
4. +21.4 Date Objects
+22 Text Processing
1. +22.1 String Objects
2. +22.2 RegExp (Regular Expression) Objects
+23 Indexed Collections
1. +23.1 Array Objects
2. +23.2 TypedArray Objects
+24 Keyed Collections
1. +24.1 Map Objects
2. +24.2 Set Objects
3. +24.3 WeakMap Objects
4. +24.4 WeakSet Objects
5. +24.5 Abstract Operations for Keyed Collections
  1. 24.5.1 CanonicalizeKeyedCollectionKey ( key )
+25 Structured Data
1. +25.1 ArrayBuffer Objects
2. +25.2 SharedArrayBuffer Objects
3. +25.3 DataView Objects
4. +25.4 The Atomics Object
5. +25.5 The JSON Object
+26 Managing Memory
1. +26.1 WeakRef Objects
2. +26.2 FinalizationRegistry Objects
+27 Control Abstraction Objects
1. +27.1 Iteration
2. +27.2 Promise Objects
3. +27.3 GeneratorFunction Objects
4. +27.4 AsyncGeneratorFunction Objects
5. +27.5 Generator Objects
6. +27.6 AsyncGenerator Objects
7. +27.7 AsyncFunction Objects
+28 Reflection
1. +28.1 The Reflect Object
2. +28.2 Proxy Objects
  1. +28.2.1 The Proxy Constructor
    1. 28.2.1.1 Proxy ( target, handler )
  2. +28.2.2 Properties of the Proxy Constructor
    1. 28.2.2.1 Proxy.revocable ( target, handler )
3. +28.3 Module Namespace Objects
  1. 28.3.1 %Symbol.toStringTag%
+29 Memory Model
1. 29.1 Memory Model Fundamentals
2. 29.2 Agent Events Records
3. 29.3 Chosen Value Records
4. 29.4 Candidate Executions
5. +29.5 Abstract Operations for the Memory Model
6. +29.6 Relations of Candidate Executions
7. +29.7 Properties of Valid Executions
8. 29.8 Races
9. 29.9 Data Races
10. 29.10 Data Race Freedom
11. 29.11 Shared Memory Guidelines
+A Grammar Summary
1. A.1 Lexical Grammar
2. A.2 Expressions
3. A.3 Statements
4. A.4 Functions and Classes
5. A.5 Scripts and Modules
6. A.6 Number Conversions
7. A.7 Time Zone Offset String Format
8. A.8 Regular Expressions
+B Additional ECMAScript Features for Web Browsers
1. +B.1 Additional Syntax
  1. B.1.1 HTML-like Comments
  2. +B.1.2 Regular Expressions Patterns
2. +B.2 Additional Built-in Properties
3. +B.3 Other Additional Features
C The Strict Mode of ECMAScript
+D Host Layering Points
1. D.1 Host Hooks
2. D.2 Host-defined Fields
3. D.3 Host-defined Objects
4. D.4 Running Jobs
5. D.5 Internal Methods of Exotic Objects
6. D.6 Built-in Objects and Methods
E Corrections and Clarifications in ECMAScript 2015 with Possible Compatibility Impact
F Additions and Changes That Introduce Incompatibilities with Prior Editions
G Colophon
H Bibliography
I Copyright & Software License

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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 reserved words” noted in subclause 12.7.2 of this specification.

A conforming implementation of ECMAScript must not implement any extension that is listed as a Forbidden Extension in subclause 17.1.

A conforming implementation of ECMAScript must not redefine any facilities that are not implementation-defined, implementation-approximated, or host-defined.

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.

Normative Optional

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.

Normative Optional, Legacy

2.3 Example Legacy Normative Optional Clause Heading

Example clause contents.