ECMAScript® 2021 Language Specification

Introduction

Main Content

1. Scope
2. Conformance
3. Normative References
4. Overview
   1. Web Scripting
   2. Hosts and Implementations
   3. ECMAScript Overview
   4. Terms and Definitions
   5. Organization of This Specification
5. Notational Conventions
   1. Syntactic and Lexical Grammars
   2. Algorithm Conventions
6. ECMAScript Data Types and Values
   1. ECMAScript Language Types
   2. ECMAScript Specification Types
7. Abstract Operations
   1. Type Conversion
   2. Testing and Comparison Operations
   3. Operations on Objects
   4. Operations on Iterator Objects
8. Executable Code and Execution Contexts
   1. Environment Records
   2. Realms
   3. Execution Contexts
   4. Jobs and Host Operations to Enqueue Jobs
   5. InitializeHostDefinedRealm ( )
   6. Agents
   7. Agent Clusters
   8. Forward Progress
   9. Processing Model of WeakRef and FinalizationRegistry Objects
   10. ClearKeptObjects ( )
   11. AddToKeptObjects ( object )
   12. CleanupFinalizationRegistry ( finalizationRegistry )
9. Ordinary and Exotic Objects Behaviours
   1. Ordinary Object Internal Methods and Internal Slots
   2. ECMAScript Function Objects
   3. Built-in Function Objects
   4. Built-in Exotic Object Internal Methods and Slots
   5. Proxy Object Internal Methods and Internal Slots
10. ECMAScript Language: Source Code
    1. Source Text
    2. Types of Source Code
11. ECMAScript Language: Lexical Grammar
    1. Unicode Format-Control Characters
    2. White Space
    3. Line Terminators
    4. Comments
    5. Tokens
    6. Names and Keywords
    7. Punctuators
    8. Literals
    9. Automatic Semicolon Insertion
    10. Interesting Cases of Automatic Semicolon Insertion
    11. Cases of Automatic Semicolon Insertion and “[no LineTerminator here]”
12. ECMAScript Language: Expressions
    1. Identifiers
    2. Primary Expression
    3. Left-Hand-Side Expressions
    4. Update Expressions
    5. Unary Operators
    6. Exponentiation Operator
    7. Multiplicative Operators
    8. Additive Operators
    9. Bitwise Shift Operators
    10. Relational Operators
    11. Equality Operators
    12. Binary Bitwise Operators
    13. Binary Logical Operators
    14. Conditional Operator ( ? : )
    15. Assignment Operators
    16. Comma Operator ( , )
13. ECMAScript Language: Statements and Declarations
    1. Statement Semantics
    2. Block
    3. Declarations and the Variable Statement
    4. Empty Statement
    5. Expression Statement
    6. The if Statement
    7. Iteration Statements
    8. The continue Statement
    9. The break Statement
    10. The return Statement
    11. The with Statement
    12. The switch Statement
    13. Labelled Statements
    14. The throw Statement
    15. The try Statement
    16. The debugger Statement
14. ECMAScript Language: Functions and Classes
    1. Function Definitions
    2. Arrow Function Definitions
    3. Method Definitions
    4. Generator Function Definitions
    5. Async Generator Function Definitions
    6. Class Definitions
    7. Async Function Definitions
    8. Async Arrow Function Definitions
    9. Tail Position Calls
15. ECMAScript Language: Scripts and Modules
    1. Scripts
    2. Modules
16. Error Handling and Language Extensions
    1. Forbidden Extensions
17. ECMAScript Standard Built-in Objects
18. The Global Object
    1. Value Properties of the Global Object
    2. Function Properties of the Global Object
    3. Constructor Properties of the Global Object
    4. Other Properties of the Global Object
19. Fundamental Objects
    1. Object Objects
    2. Function Objects
    3. Boolean Objects
    4. Symbol Objects
    5. Error Objects
20. Numbers and Dates
    1. Number Objects
    2. BigInt Objects
    3. The Math Object
    4. Date Objects
21. Text Processing
    1. String Objects
    2. RegExp (Regular Expression) Objects
22. Indexed Collections
    1. Array Objects
    2. TypedArray Objects
23. Keyed Collections
    1. Map Objects
    2. Set Objects
    3. WeakMap Objects
    4. WeakSet Objects
24. Structured Data
    1. ArrayBuffer Objects
    2. SharedArrayBuffer Objects
    3. DataView Objects
    4. The Atomics Object
    5. The JSON Object
25. Managing Memory
    1. WeakRef Objects
    2. FinalizationRegistry Objects
26. Control Abstraction Objects
    1. Iteration
    2. GeneratorFunction Objects
    3. AsyncGeneratorFunction Objects
    4. Generator Objects
    5. AsyncGenerator Objects
    6. Promise Objects
    7. AsyncFunction Objects
27. Reflection
    1. The Reflect Object
    2. Proxy Objects
    3. Module Namespace Objects
28. Memory Model
    1. Memory Model Fundamentals
    2. Agent Events Records
    3. Chosen Value Records
    4. Candidate Executions
    5. Abstract Operations for the Memory Model
    6. Relations of Candidate Executions
    7. Properties of Valid Executions
    8. Races
    9. Data Races
    10. Data Race Freedom
    11. Shared Memory Guidelines

Appendix

1. Grammar Summary
   1. Lexical Grammar
   2. Expressions
   3. Statements
   4. Functions and Classes
   5. Scripts and Modules
   6. Number Conversions
   7. Universal Resource Identifier Character Classes
   8. Regular Expressions
2. Additional ECMAScript Features for Web Browsers
   1. Additional Syntax
   2. Additional Built-in Properties
   3. Other Additional Features
3. The Strict Mode of ECMAScript
4. Host Layering Points
   1. Host Hooks
   2. Host-defined Fields
   3. Host-defined Objects
   4. Running Jobs
   5. Internal Methods of Exotic Objects
   6. Built-in Objects and Methods
5. Corrections and Clarifications in ECMAScript 2015 with Possible Compatibility Impact
6. Additions and Changes That Introduce Incompatibilities with Prior Editions
7. Colophon
8. Bibliography
9. Copyright & Software License