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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E Corrections and Clarifications in ECMAScript 2015 with Possible Compatibility Impact

9.1.1.4.15-9.1.1.4.18 Edition 5 and 5.1 used a property existence test to determine whether a global object property corresponding to a new global declaration already existed. ECMAScript 2015 uses an own property existence test. This corresponds to what has been most commonly implemented by web browsers.

10.4.2.1: The 5^th Edition moved the capture of the current array length prior to the integer conversion of the array index or new length value. However, the captured length value could become invalid if the conversion process has the side-effect of changing the array length. ECMAScript 2015 specifies that the current array length must be captured after the possible occurrence of such side-effects.

21.4.1.31: Previous editions permitted the TimeClip abstract operation to return either +0_𝔽 or -0_𝔽 as the representation of a 0 time value. ECMAScript 2015 specifies that +0_𝔽 always returned. This means that for ECMAScript 2015 the time value of a Date is never observably -0_𝔽 and methods that return time values never return -0_𝔽.

21.4.1.32: If a UTC offset representation is not present, the local time zone is used. Edition 5.1 incorrectly stated that a missing time zone should be interpreted as "z".

21.4.4.36: If the year cannot be represented using the Date Time String Format specified in 21.4.1.32 a RangeError exception is thrown. Previous editions did not specify the behaviour for that case.

21.4.4.41: Previous editions did not specify the value returned by Date.prototype.toString when the time value is NaN. ECMAScript 2015 specifies the result to be the String value "Invalid Date".

22.2.4.1, 22.2.6.13.1: Any LineTerminator code points in the value of the "source" property of a RegExp instance must be expressed using an escape sequence. Edition 5.1 only required the escaping of /.

22.2.6.8, 22.2.6.11: In previous editions, the specifications for String.prototype.match and String.prototype.replace was incorrect for cases where the pattern argument was a RegExp value whose global flag is set. The previous specifications stated that for each attempt to match the pattern, if lastIndex did not change, it should be incremented by 1. The correct behaviour is that lastIndex should be incremented by 1 only if the pattern matched the empty String.

23.1.3.30: Previous editions did not specify how a NaN value returned by a comparator was interpreted by Array.prototype.sort. ECMAScript 2015 specifies that such as value is treated as if +0_𝔽 was returned from the comparator. ECMAScript 2015 also specifies that ToNumber is applied to the result returned by a comparator. In previous editions, the effect of a comparator result that is not a Number value was implementation-defined. In practice, implementations call ToNumber.