Reference number ECMA-123:2009

Ecma International 2009

ECMA-262 6th Edition / June 2015

ECMAScript 2015 Language Specification

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Ecma International 2015

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Ecma International 2015 iii

Contents Page

1 Scope .............................................................................................................................................1

2 Conformance .................................................................................................................................1

3 Normative references ....................................................................................................................1

4 Overview ........................................................................................................................................1 4.1 Web Scripting ................................................................................................................................2 4.2 ECMAScript Overview ...................................................................................................................2

Objects...........................................................................................................................................3 4.2.1 The Strict Variant of ECMAScript .................................................................................................4 4.2.2

4.3 Terms and definitions ...................................................................................................................5 4.4 Organization of This Specification ...............................................................................................8

5 Notational Conventions ................................................................................................................8 5.1 Syntactic and Lexical Grammars ..................................................................................................8

Context-Free Grammars................................................................................................................8 5.1.1 The Lexical and RegExp Grammars .............................................................................................9 5.1.2 The Numeric String Grammar .......................................................................................................9 5.1.3 The Syntactic Grammar ................................................................................................................9 5.1.4 Grammar Notation ....................................................................................................................... 10 5.1.5

5.2 Algorithm Conventions ............................................................................................................... 14 5.3 Static Semantic Rules ................................................................................................................. 16

6 ECMAScript Data Types and Values .......................................................................................... 16 6.1 ECMAScript Language Types ..................................................................................................... 16

The Undefined Type .................................................................................................................... 16 6.1.1 The Null Type............................................................................................................................... 17 6.1.2 The Boolean Type ....................................................................................................................... 17 6.1.3 The String Type ........................................................................................................................... 17 6.1.4 The Symbol Type......................................................................................................................... 17 6.1.5 The Number Type ........................................................................................................................ 18 6.1.6 The Object Type .......................................................................................................................... 19 6.1.7

6.2 ECMAScript Specification Types ................................................................................................ 29 The List and Record Specification Type .................................................................................... 29 6.2.1 The Completion Record Specification Type .............................................................................. 30 6.2.2 The Reference Specification Type .............................................................................................. 31 6.2.3 The Property Descriptor Specification Type .............................................................................. 33 6.2.4 The Lexical Environment and Environment Record Specification Types ................................ 35 6.2.5 Data Blocks ................................................................................................................................. 35 6.2.6

7 Abstract Operations .................................................................................................................... 36 7.1 Type Conversion ......................................................................................................................... 36

ToPrimitive ( input [, PreferredType] ) ........................................................................................ 36 7.1.1 ToBoolean ( argument ) .............................................................................................................. 37 7.1.2 ToNumber ( argument ) ............................................................................................................... 38 7.1.3 ToInteger ( argument ) ................................................................................................................ 40 7.1.4 ToInt32 ( argument ) .................................................................................................................... 40 7.1.5 ToUint32 ( argument ) ................................................................................................................. 41 7.1.6 ToInt16 ( argument ) .................................................................................................................... 41 7.1.7 ToUint16 ( argument ) ................................................................................................................. 41 7.1.8 ToInt8 ( argument ) ...................................................................................................................... 41 7.1.9

ToUint8 ( argument ) ................................................................................................................... 42 7.1.10 ToUint8Clamp ( argument ) ......................................................................................................... 42 7.1.11 ToString ( argument ) .................................................................................................................. 42 7.1.12

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ToObject ( argument ) ................................................................................................................. 43 7.1.13 ToPropertyKey ( argument ) ....................................................................................................... 44 7.1.14 ToLength ( argument ) ................................................................................................................ 44 7.1.15 CanonicalNumericIndexString ( argument ) .............................................................................. 44 7.1.16

7.2 Testing and Comparison Operations ......................................................................................... 45 RequireObjectCoercible ( argument ) ........................................................................................ 45 7.2.1 IsArray ( argument ) .................................................................................................................... 45 7.2.2 IsCallable ( argument ) ................................................................................................................ 45 7.2.3 IsConstructor ( argument ) ......................................................................................................... 45 7.2.4 IsExtensible (O) ........................................................................................................................... 45 7.2.5 IsInteger ( argument ).................................................................................................................. 46 7.2.6 IsPropertyKey ( argument ) ........................................................................................................ 46 7.2.7 IsRegExp ( argument ) ................................................................................................................ 46 7.2.8 SameValue(x, y) .......................................................................................................................... 46 7.2.9

SameValueZero(x, y) ................................................................................................................... 46 7.2.10 Abstract Relational Comparison ................................................................................................ 47 7.2.11 Abstract Equality Comparison ................................................................................................... 48 7.2.12 Strict Equality Comparison ........................................................................................................ 48 7.2.13

7.3 Operations on Objects ................................................................................................................ 49 Get (O, P) ..................................................................................................................................... 49 7.3.1 GetV (V, P) ................................................................................................................................... 49 7.3.2 Set (O, P, V, Throw) ..................................................................................................................... 49 7.3.3 CreateDataProperty (O, P, V) ...................................................................................................... 49 7.3.4 CreateMethodProperty (O, P, V) ................................................................................................. 50 7.3.5 CreateDataPropertyOrThrow (O, P, V)........................................................................................ 50 7.3.6 DefinePropertyOrThrow (O, P, desc) .......................................................................................... 50 7.3.7 DeletePropertyOrThrow (O, P) .................................................................................................... 50 7.3.8 GetMethod (O, P) ......................................................................................................................... 51 7.3.9

HasProperty (O, P) ...................................................................................................................... 51 7.3.10 HasOwnProperty (O, P) ............................................................................................................... 51 7.3.11 Call(F, V, [argumentsList]) .......................................................................................................... 51 7.3.12 Construct (F, [argumentsList], [newTarget]) ............................................................................. 51 7.3.13 SetIntegrityLevel (O, level) ......................................................................................................... 52 7.3.14 TestIntegrityLevel (O, level) ........................................................................................................ 52 7.3.15 CreateArrayFromList (elements) ................................................................................................ 52 7.3.16 CreateListFromArrayLike (obj [, elementTypes] )...................................................................... 53 7.3.17 Invoke(O,P, [argumentsList]) ...................................................................................................... 53 7.3.18 OrdinaryHasInstance (C, O) ........................................................................................................ 53 7.3.19 SpeciesConstructor ( O, defaultConstructor ) ........................................................................... 54 7.3.20 EnumerableOwnNames (O) ........................................................................................................ 54 7.3.21 GetFunctionRealm ( obj ) ............................................................................................................ 54 7.3.22

7.4 Operations on Iterator Objects ................................................................................................... 54 GetIterator ( obj, method ) .......................................................................................................... 55 7.4.1 IteratorNext ( iterator, value )...................................................................................................... 55 7.4.2 IteratorComplete ( iterResult ) .................................................................................................... 55 7.4.3 IteratorValue ( iterResult ) ........................................................................................................... 55 7.4.4 IteratorStep ( iterator ) ................................................................................................................ 55 7.4.5 IteratorClose( iterator, completion ) ........................................................................................... 55 7.4.6 CreateIterResultObject ( value, done ) ....................................................................................... 56 7.4.7 CreateListIterator ( list ) .............................................................................................................. 56 7.4.8

8 Executable Code and Execution Contexts................................................................................. 56 8.1 Lexical Environments ................................................................................................................. 56

Environment Records ................................................................................................................. 57 8.1.1 Lexical Environment Operations ................................................................................................ 71 8.1.2

8.2 Code Realms ............................................................................................................................... 72 CreateRealm ( )............................................................................................................................ 73 8.2.1 CreateIntrinsics ( realmRec ) ...................................................................................................... 73 8.2.2 SetRealmGlobalObject ( realmRec, globalObj ) ......................................................................... 73 8.2.3 SetDefaultGlobalBindings ( realmRec ) ..................................................................................... 73 8.2.4

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8.3 Execution Contexts ..................................................................................................................... 74 ResolveBinding ( name, [env] )................................................................................................... 75 8.3.1 GetThisEnvironment ( ) ............................................................................................................... 75 8.3.2 ResolveThisBinding ( ) ................................................................................................................ 75 8.3.3 GetNewTarget ( ).......................................................................................................................... 75 8.3.4 GetGlobalObject ( ) ...................................................................................................................... 76 8.3.5

8.4 Jobs and Job Queues ................................................................................................................. 76 EnqueueJob (queueName, job, arguments) ............................................................................... 77 8.4.1 NextJob result ............................................................................................................................. 77 8.4.2

8.5 ECMAScript Initialization() .......................................................................................................... 77 InitializeHostDefinedRealm ( realm ) .......................................................................................... 78 8.5.1

9 Ordinary and Exotic Objects Behaviours ................................................................................... 78 9.1 Ordinary Object Internal Methods and Internal Slots ................................................................ 78

[[GetPrototypeOf]] ( )................................................................................................................... 78 9.1.1 [[SetPrototypeOf]] (V) .................................................................................................................. 78 9.1.2 [[IsExtensible]] ( ) ........................................................................................................................ 79 9.1.3 [[PreventExtensions]] ( ) ............................................................................................................. 79 9.1.4 [[GetOwnProperty]] (P) ............................................................................................................... 79 9.1.5 [[DefineOwnProperty]] (P, Desc) ................................................................................................ 79 9.1.6 [[HasProperty]](P) ....................................................................................................................... 81 9.1.7 [[Get]] (P, Receiver) ..................................................................................................................... 81 9.1.8 [[Set]] ( P, V, Receiver) ................................................................................................................ 81 9.1.9

[[Delete]] (P) ................................................................................................................................. 82 9.1.10 [[Enumerate]] () ........................................................................................................................... 82 9.1.11 [[OwnPropertyKeys]] ( ) .............................................................................................................. 83 9.1.12 ObjectCreate(proto, internalSlotsList) ....................................................................................... 83 9.1.13 OrdinaryCreateFromConstructor ( constructor, intrinsicDefaultProto, internalSlotsList ) ..... 83 9.1.14 GetPrototypeFromConstructor ( constructor, intrinsicDefaultProto ) ...................................... 84 9.1.15

9.2 ECMAScript Function Objects .................................................................................................... 84 [[Call]] ( thisArgument, argumentsList) ...................................................................................... 85 9.2.1 [[Construct]] ( argumentsList, newTarget) ................................................................................. 86 9.2.2 FunctionAllocate (functionPrototype, strict [,functionKind] ) ................................................... 87 9.2.3 FunctionInitialize (F, kind, ParameterList, Body, Scope) .......................................................... 87 9.2.4 FunctionCreate (kind, ParameterList, Body, Scope, Strict, prototype) ..................................... 88 9.2.5 GeneratorFunctionCreate (kind, ParameterList, Body, Scope, Strict) ...................................... 88 9.2.6 AddRestrictedFunctionProperties ( F, realm ) ........................................................................... 88 9.2.7 MakeConstructor (F, writablePrototype, prototype) .................................................................. 88 9.2.8 MakeClassConstructor ( F) ......................................................................................................... 89 9.2.9

MakeMethod ( F, homeObject) .................................................................................................... 89 9.2.10 SetFunctionName (F, name, prefix) ............................................................................................ 89 9.2.11 FunctionDeclarationInstantiation(func, argumentsList) ............................................................ 89 9.2.12

9.3 Built-in Function Objects ............................................................................................................ 92 [[Call]] ( thisArgument, argumentsList) ...................................................................................... 92 9.3.1 [[Construct]] (argumentsList, newTarget) .................................................................................. 93 9.3.2 CreateBuiltinFunction(realm, steps, prototype, internalSlotsList) ........................................... 93 9.3.3

9.4 Built-in Exotic Object Internal Methods and Slots ..................................................................... 93 Bound Function Exotic Objects .................................................................................................. 93 9.4.1 Array Exotic Objects ................................................................................................................... 95 9.4.2 String Exotic Objects .................................................................................................................. 97 9.4.3 Arguments Exotic Objects .......................................................................................................... 98 9.4.4 Integer Indexed Exotic Objects................................................................................................. 102 9.4.5 Module Namespace Exotic Objects .......................................................................................... 105 9.4.6

9.5 Proxy Object Internal Methods and Internal Slots ................................................................... 108 [[GetPrototypeOf]] ( )................................................................................................................. 109 9.5.1 [[SetPrototypeOf]] (V) ................................................................................................................ 109 9.5.2 [[IsExtensible]] ( ) ...................................................................................................................... 110 9.5.3 [[PreventExtensions]] ( ) ........................................................................................................... 110 9.5.4 [[GetOwnProperty]] (P) ............................................................................................................. 111 9.5.5 [[DefineOwnProperty]] (P, Desc) .............................................................................................. 111 9.5.6

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[[HasProperty]] (P) .................................................................................................................... 112 9.5.7 [[Get]] (P, Receiver) ................................................................................................................... 113 9.5.8 [[Set]] ( P, V, Receiver) .............................................................................................................. 113 9.5.9

[[Delete]] (P) .............................................................................................................................. 114 9.5.10 [[Enumerate]] () ......................................................................................................................... 114 9.5.11 [[OwnPropertyKeys]] ( ) ............................................................................................................ 114 9.5.12 [[Call]] (thisArgument, argumentsList) .................................................................................... 115 9.5.13 [[Construct]] ( argumentsList, newTarget)............................................................................... 116 9.5.14 ProxyCreate(target, handler) .................................................................................................... 116 9.5.15

10 ECMAScript Language: Source Code ...................................................................................... 116 10.1 Source Text ............................................................................................................................... 116

Static Semantics: UTF16Encoding ( cp ) ................................................................................ 117 10.1.1 Static Semantics: UTF16Decode( lead, trail )........................................................................... 117 10.1.2

10.2 Types of Source Code .............................................................................................................. 117 Strict Mode Code ...................................................................................................................... 118 10.2.1 Non-ECMAScript Functions...................................................................................................... 118 10.2.2

11 ECMAScript Language: Lexical Grammar ............................................................................... 118 11.1 Unicode Format-Control Characters ........................................................................................ 119 11.2 White Space .............................................................................................................................. 120 11.3 Line Terminators ....................................................................................................................... 121 11.4 Comments ................................................................................................................................. 121 11.5 Tokens ....................................................................................................................................... 122 11.6 Names and Keywords ............................................................................................................... 122

Identifier Names ........................................................................................................................ 123 11.6.1 Reserved Words ........................................................................................................................ 124 11.6.2

11.7 Punctuators ............................................................................................................................... 125 11.8 Literals ....................................................................................................................................... 125

Null Literals ............................................................................................................................... 125 11.8.1 Boolean Literals ........................................................................................................................ 125 11.8.2 Numeric Literals ........................................................................................................................ 125 11.8.3 String Literals ............................................................................................................................ 128 11.8.4 Regular Expression Literals ..................................................................................................... 131 11.8.5 Template Literal Lexical Components...................................................................................... 132 11.8.6

11.9 Automatic Semicolon Insertion ................................................................................................ 134 Rules of Automatic Semicolon Insertion ................................................................................. 135 11.9.1 Examples of Automatic Semicolon Insertion........................................................................... 136 11.9.2

12 ECMAScript Language: Expressions ....................................................................................... 137 12.1 Identifiers .................................................................................................................................. 137

Static Semantics: Early Errors ................................................................................................ 137 12.1.1 Static Semantics: BoundNames ............................................................................................... 138 12.1.2 Static Semantics: IsValidSimpleAssignmentTarget ............................................................... 138 12.1.3 Static Semantics: StringValue .................................................................................................. 138 12.1.4 Runtime Semantics: BindingInitialization ................................................................................ 138 12.1.5 Runtime Semantics: Evaluation .............................................................................................. 139 12.1.6

12.2 Primary Expression .................................................................................................................. 139 Semantics .................................................................................................................................. 140 12.2.1 The this Keyword .................................................................................................................... 141 12.2.2 Identifier Reference ................................................................................................................... 141 12.2.3 Literals ....................................................................................................................................... 141 12.2.4 Array Initializer .......................................................................................................................... 142 12.2.5 Object Initializer ........................................................................................................................ 144 12.2.6 Function Defining Expressions ................................................................................................ 148 12.2.7 Regular Expression Literals ..................................................................................................... 148 12.2.8 Template Literals ...................................................................................................................... 148 12.2.9

The Grouping Operator ............................................................................................................. 152 12.2.1012.3 Left-Hand-Side Expressions ..................................................................................................... 153

Static Semantics ....................................................................................................................... 153 12.3.1 Property Accessors .................................................................................................................. 156 12.3.2

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The new Operator ...................................................................................................................... 157 12.3.3 Function Calls ........................................................................................................................... 157 12.3.4 The super Keyword .................................................................................................................. 159 12.3.5 Argument Lists .......................................................................................................................... 160 12.3.6 Tagged Templates ..................................................................................................................... 160 12.3.7 Meta Properties ......................................................................................................................... 161 12.3.8

12.4 Postfix Expressions .................................................................................................................. 161 Static Semantics: Early Errors................................................................................................. 161 12.4.1 Static Semantics: IsFunctionDefinition ................................................................................... 161 12.4.2 Static Semantics: IsValidSimpleAssignmentTarget ............................................................... 161 12.4.3 Postfix Increment Operator....................................................................................................... 162 12.4.4 Postfix Decrement Operator ..................................................................................................... 162 12.4.5

12.5 Unary Operators ........................................................................................................................ 162 Static Semantics: Early Errors................................................................................................. 162 12.5.1 Static Semantics: IsFunctionDefinition ................................................................................... 162 12.5.2 Static Semantics: IsValidSimpleAssignmentTarget ............................................................... 163 12.5.3 The delete Operator ................................................................................................................ 163 12.5.4 The void Operator .................................................................................................................... 164 12.5.5 The typeof Operator ................................................................................................................ 164 12.5.6 Prefix Increment Operator ........................................................................................................ 165 12.5.7 Prefix Decrement Operator ....................................................................................................... 165 12.5.8 Unary + Operator ....................................................................................................................... 165 12.5.9

Unary - Operator ....................................................................................................................... 165 12.5.10 Bitwise NOT Operator ( ~ ) ........................................................................................................ 166 12.5.11 Logical NOT Operator ( ! ) ........................................................................................................ 166 12.5.12

12.6 Multiplicative Operators ............................................................................................................ 166 Static Semantics: IsFunctionDefinition ................................................................................... 166 12.6.1 Static Semantics: IsValidSimpleAssignmentTarget ............................................................... 166 12.6.2 Runtime Semantics: Evaluation .............................................................................................. 166 12.6.3

12.7 Additive Operators .................................................................................................................... 168 Static Semantics: IsFunctionDefinition ................................................................................... 168 12.7.1 Static Semantics: IsValidSimpleAssignmentTarget ............................................................... 168 12.7.2 The Addition operator ( + ) ........................................................................................................ 169 12.7.3 The Subtraction Operator ( - ) .................................................................................................. 169 12.7.4 Applying the Additive Operators to Numbers .......................................................................... 169 12.7.5

12.8 Bitwise Shift Operators ............................................................................................................. 170 Static Semantics: IsFunctionDefinition ................................................................................... 170 12.8.1 Static Semantics: IsValidSimpleAssignmentTarget ............................................................... 170 12.8.2 The Left Shift Operator ( > ) ..................................................................................... 171 12.8.4 The Unsigned Right Shift Operator ( >>> ) ............................................................................... 171 12.8.5

12.9 Relational Operators ................................................................................................................. 172 Static Semantics: IsFunctionDefinition ................................................................................... 172 12.9.1 Static Semantics: IsValidSimpleAssignmentTarget ............................................................... 172 12.9.2 Runtime Semantics: Evaluation .............................................................................................. 172 12.9.3 Runtime Semantics: InstanceofOperator(O, C) ....................................................................... 174 12.9.4

12.10 Equality Operators .................................................................................................................... 174 Static Semantics: IsFunctionDefinition ................................................................................... 174 12.10.1 Static Semantics: IsValidSimpleAssignmentTarget ............................................................... 174 12.10.2 Runtime Semantics: Evaluation .............................................................................................. 174 12.10.3

12.11 Binary Bitwise Operators .......................................................................................................... 176 Static Semantics: IsFunctionDefinition ................................................................................... 176 12.11.1 Static Semantics: IsValidSimpleAssignmentTarget ............................................................... 176 12.11.2 Runtime Semantics: Evaluation .............................................................................................. 176 12.11.3

12.12 Binary Logical Operators .......................................................................................................... 177 Static Semantics: IsFunctionDefinition ................................................................................... 177 12.12.1 Static Semantics: IsValidSimpleAssignmentTarget ............................................................... 177 12.12.2 Runtime Semantics: Evaluation .............................................................................................. 177 12.12.3

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12.13 Conditional Operator ( ? : ) .................................................................................................. 178 Static Semantics: IsFunctionDefinition ................................................................................... 178 12.13.1 Static Semantics: IsValidSimpleAssignmentTarget ............................................................... 178 12.13.2 Runtime Semantics: Evaluation .............................................................................................. 178 12.13.3

12.14 Assignment Operators .............................................................................................................. 178 Static Semantics: Early Errors ................................................................................................ 179 12.14.1 Static Semantics: IsFunctionDefinition ................................................................................... 179 12.14.2 Static Semantics: IsValidSimpleAssignmentTarget ............................................................... 179 12.14.3 Runtime Semantics: Evaluation .............................................................................................. 179 12.14.4 Destructuring Assignment ....................................................................................................... 180 12.14.5

12.15 Comma Operator ( , ) ............................................................................................................. 185 Static Semantics: IsFunctionDefinition ................................................................................... 185 12.15.1 Static Semantics: IsValidSimpleAssignmentTarget ............................................................... 185 12.15.2 Runtime Semantics: Evaluation .............................................................................................. 186 12.15.3

13 ECMAScript Language: Statements and Declarations ............................................................ 186 13.1 Statement Semantics ................................................................................................................ 186

Static Semantics: ContainsDuplicateLabels ............................................................................ 186 13.1.1 Static Semantics: ContainsUndefinedBreakTarget ................................................................. 187 13.1.2 Static Semantics: ContainsUndefinedContinueTarget ............................................................ 187 13.1.3 Static Semantics: DeclarationPart........................................................................................... 187 13.1.4 Static Semantics: VarDeclaredNames..................................................................................... 188 13.1.5 Static Semantics: VarScopedDeclarations ............................................................................. 188 13.1.6 Runtime Semantics: LabelledEvaluation ............................................................................... 188 13.1.7 Runtime Semantics: Evaluation .............................................................................................. 188 13.1.8

13.2 Block .......................................................................................................................................... 189 Static Semantics: Early Errors ................................................................................................ 189 13.2.1 Static Semantics: ContainsDuplicateLabels ............................................................................ 189 13.2.2 Static Semantics: ContainsUndefinedBreakTarget ................................................................. 189 13.2.3 Static Semantics: ContainsUndefinedContinueTarget ............................................................ 190 13.2.4 Static Semantics: LexicallyDeclaredNames ........................................................................... 190 13.2.5 Static Semantics: LexicallyScopedDeclarations .................................................................... 190 13.2.6 Static Semantics: TopLevelLexicallyDeclaredNames ............................................................ 191 13.2.7 Static Semantics: TopLevelLexicallyScopedDeclarations ..................................................... 191 13.2.8 Static Semantics: TopLevelVarDeclaredNames ..................................................................... 192 13.2.9

Static Semantics: TopLevelVarScopedDeclarations .............................................................. 192 13.2.10 Static Semantics: VarDeclaredNames..................................................................................... 192 13.2.11 Static Semantics: VarScopedDeclarations ............................................................................. 193 13.2.12 Runtime Semantics: Evaluation .............................................................................................. 193 13.2.13 Runtime Semantics: BlockDeclarationInstantiation( code, env ) ........................................... 194 13.2.14

13.3 Declarations and the Variable Statement ................................................................................. 194 Let and Const Declarations ...................................................................................................... 194 13.3.1 Variable Statement .................................................................................................................... 196 13.3.2 Destructuring Binding Patterns................................................................................................ 198 13.3.3

13.4 Empty Statement ....................................................................................................................... 205 Runtime Semantics: Evaluation .............................................................................................. 205 13.4.1

13.5 Expression Statement............................................................................................................... 205 Runtime Semantics: Evaluation .............................................................................................. 205 13.5.1

13.6 The if Statement ...................................................................................................................... 205 Static Semantics: Early Errors ................................................................................................ 205 13.6.1 Static Semantics: ContainsDuplicateLabels ............................................................................ 205 13.6.2 Static Semantics: ContainsUndefinedBreakTarget ................................................................. 206 13.6.3 Static Semantics: ContainsUndefinedContinueTarget ............................................................ 206 13.6.4 Static Semantics: VarDeclaredNames..................................................................................... 206 13.6.5 Static Semantics: VarScopedDeclarations ............................................................................. 206 13.6.6 Runtime Semantics: Evaluation ............................................................................................. 207 13.6.7

13.7 Iteration Statements .................................................................................................................. 207 Semantics .................................................................................................................................. 208 13.7.1 The do-while Statement .......................................................................................................... 208 13.7.2

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The while Statement ................................................................................................................ 209 13.7.3 The for Statement .................................................................................................................... 210 13.7.4 The for-in and for-of Statements ......................................................................................... 213 13.7.5

13.8 The continue Statement .......................................................................................................... 219 Static Semantics: Early Errors................................................................................................. 219 13.8.1 Static Semantics: ContainsUndefinedContinueTarget ............................................................ 219 13.8.2 Runtime Semantics: Evaluation .............................................................................................. 219 13.8.3

13.9 The break Statement ................................................................................................................ 219 Static Semantics: Early Errors................................................................................................. 219 13.9.1 Static Semantics: ContainsUndefinedBreakTarget ................................................................. 219 13.9.2 Runtime Semantics: Evaluation .............................................................................................. 220 13.9.3

13.10 The return Statement .............................................................................................................. 220 Runtime Semantics: Evaluation .............................................................................................. 220 13.10.1

13.11 The with Statement .................................................................................................................. 220 Static Semantics: Early Errors................................................................................................. 220 13.11.1 Static Semantics: ContainsDuplicateLabels ............................................................................ 221 13.11.2 Static Semantics: ContainsUndefinedBreakTarget ................................................................. 221 13.11.3 Static Semantics: ContainsUndefinedContinueTarget ............................................................ 221 13.11.4 Static Semantics: VarDeclaredNames ..................................................................................... 221 13.11.5 Static Semantics: VarScopedDeclarations ............................................................................. 221 13.11.6 Runtime Semantics: Evaluation .............................................................................................. 221 13.11.7

13.12 The switch Statement .............................................................................................................. 222 Static Semantics: Early Errors................................................................................................. 222 13.12.1 Static Semantics: ContainsDuplicateLabels ............................................................................ 222 13.12.2 Static Semantics: ContainsUndefinedBreakTarget ................................................................. 223 13.12.3 Static Semantics: ContainsUndefinedContinueTarget ............................................................ 223 13.12.4 Static Semantics: LexicallyDeclaredNames ............................................................................ 224 13.12.5 Static Semantics: LexicallyScopedDeclarations .................................................................... 225 13.12.6 Static Semantics: VarDeclaredNames ..................................................................................... 225 13.12.7 Static Semantics: VarScopedDeclarations ............................................................................. 226 13.12.8 Runtime Semantics: CaseBlockEvaluation ............................................................................. 226 13.12.9

Runtime Semantics: CaseSelectorEvaluation ........................................................................ 228 13.12.10 Runtime Semantics: Evaluation .............................................................................................. 228 13.12.11

13.13 Labelled Statements.................................................................................................................. 228 Static Semantics: Early Errors................................................................................................. 229 13.13.1 Static Semantics: ContainsDuplicateLabels ............................................................................ 229 13.13.2 Static Semantics: ContainsUndefinedBreakTarget ................................................................. 229 13.13.3 Static Semantics: ContainsUndefinedContinueTarget ............................................................ 229 13.13.4 Static Semantics: IsLabelledFunction ( stmt ) ........................................................................ 229 13.13.5 Static Semantics: LexicallyDeclaredNames ............................................................................ 230 13.13.6 Static Semantics: LexicallyScopedDeclarations .................................................................... 230 13.13.7 Static Semantics: TopLevelLexicallyDeclaredNames ............................................................ 230 13.13.8 Static Semantics: TopLevelLexicallyScopedDeclarations ..................................................... 230 13.13.9

Static Semantics: TopLevelVarDeclaredNames...................................................................... 230 13.13.10 Static Semantics: TopLevelVarScopedDeclarations .............................................................. 231 13.13.11 Static Semantics: VarDeclaredNames ..................................................................................... 231 13.13.12 Static Semantics: VarScopedDeclarations ............................................................................. 231 13.13.13 Runtime Semantics: LabelledEvaluation ............................................................................... 231 13.13.14 Runtime Semantics: Evaluation ............................................................................................... 232 13.13.15

13.14 The throw Statement ................................................................................................................ 232 Runtime Semantics: Evaluation .............................................................................................. 232 13.14.1

13.15 The try Statement .................................................................................................................... 232 Static Semantics: Early Errors................................................................................................. 232 13.15.1 Static Semantics: ContainsDuplicateLabels ............................................................................ 233 13.15.2 Static Semantics: ContainsUndefinedBreakTarget ................................................................. 233 13.15.3 Static Semantics: ContainsUndefinedContinueTarget ............................................................ 234 13.15.4 Static Semantics: VarDeclaredNames ..................................................................................... 234 13.15.5 Static Semantics: VarScopedDeclarations ............................................................................. 235 13.15.6 Runtime Semantics: CatchClauseEvaluation .......................................................................... 235 13.15.7

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Runtime Semantics: Evaluation .............................................................................................. 235 13.15.813.16 The debugger statement .......................................................................................................... 236

Runtime Semantics: Evaluation .............................................................................................. 236 13.16.1

14 ECMAScript Language: Functions and Classes ...................................................................... 236 14.1 Function Definitions ................................................................................................................. 236

Directive Prologues and the Use Strict Directive .................................................................... 237 14.1.1 Static Semantics: Early Errors ................................................................................................ 237 14.1.2 Static Semantics: BoundNames .............................................................................................. 238 14.1.3 Static Semantics: Contains ..................................................................................................... 238 14.1.4 Static Semantics: ContainsExpression ................................................................................... 239 14.1.5 Static Semantics: ExpectedArgumentCount .......................................................................... 239 14.1.6 Static Semantics: HasInitializer ............................................................................................... 240 14.1.7 Static Semantics: HasName .................................................................................................... 240 14.1.8 Static Semantics: IsAnonymousFunctionDefinition ( production ) ....................................... 240 14.1.9

Static Semantics: IsConstantDeclaration ............................................................................... 240 14.1.10 Static Semantics: IsFunctionDefinition ................................................................................... 240 14.1.11 Static Semantics: IsSimpleParameterList ............................................................................... 241 14.1.12 Static Semantics: LexicallyDeclaredNames ........................................................................... 241 14.1.13 Static Semantics: LexicallyScopedDeclarations .................................................................... 241 14.1.14 Static Semantics: VarDeclaredNames..................................................................................... 241 14.1.15 Static Semantics: VarScopedDeclarations ............................................................................. 242 14.1.16 Runtime Semantics: EvaluateBody ......................................................................................... 242 14.1.17 Runtime Semantics: IteratorBindingInitialization.................................................................. 242 14.1.18 Runtime Semantics: InstantiateFunctionObject ...................................................................... 243 14.1.19 Runtime Semantics: Evaluation .............................................................................................. 243 14.1.20

14.2 Arrow Function Definitions ...................................................................................................... 244 Static Semantics: Early Errors ................................................................................................ 244 14.2.1 Static Semantics: BoundNames .............................................................................................. 245 14.2.2 Static Semantics: Contains ..................................................................................................... 245 14.2.3 Static Semantics: ContainsExpression ................................................................................... 245 14.2.4 Static Semantics: ExpectedArgumentCount .......................................................................... 245 14.2.5 Static Semantics: HasInitializer ............................................................................................... 245 14.2.6 Static Semantics: HasName .................................................................................................... 246 14.2.7 Static Semantics: IsSimpleParameterList ............................................................................... 246 14.2.8 Static Semantics: CoveredFormalsList ................................................................................... 246 14.2.9

Static Semantics: LexicallyDeclaredNames ........................................................................... 246 14.2.10 Static Semantics: LexicallyScopedDeclarations .................................................................... 246 14.2.11 Static Semantics: VarDeclaredNames..................................................................................... 247 14.2.12 Static Semantics: VarScopedDeclarations ............................................................................. 247 14.2.13 Runtime Semantics: IteratorBindingInitialization.................................................................. 247 14.2.14 Runtime Semantics: EvaluateBody ......................................................................................... 247 14.2.15 Runtime Semantics: Evaluation .............................................................................................. 248 14.2.16

14.3 Method Definitions .................................................................................................................... 248 Static Semantics: Early Errors ................................................................................................ 248 14.3.1 Static Semantics: ComputedPropertyContains ...................................................................... 248 14.3.2 Static Semantics: ExpectedArgumentCount .......................................................................... 248 14.3.3 Static Semantics: HasComputedPropertyKey ........................................................................ 249 14.3.4 Static Semantics: HasDirectSuper .......................................................................................... 249 14.3.5 Static Semantics: PropName ................................................................................................... 249 14.3.6 Static Semantics: SpecialMethod ............................................................................................ 249 14.3.7 Runtime Semantics: DefineMethod .......................................................................................... 249 14.3.8 Runtime Semantics: PropertyDefinitionEvaluation ................................................................ 250 14.3.9

14.4 Generator Function Definitions ................................................................................................ 250 Static Semantics: Early Errors ................................................................................................ 251 14.4.1 Static Semantics: BoundNames .............................................................................................. 251 14.4.2 Static Semantics: ComputedPropertyContains ...................................................................... 252 14.4.3 Static Semantics: Contains ..................................................................................................... 252 14.4.4 Static Semantics: HasComputedPropertyKey ........................................................................ 252 14.4.5 Static Semantics: HasDirectSuper .......................................................................................... 252 14.4.6

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Static Semantics: HasName ..................................................................................................... 252 14.4.7 Static Semantics: IsConstantDeclaration................................................................................ 253 14.4.8 Static Semantics: IsFunctionDefinition ................................................................................... 253 14.4.9

Static Semantics: PropName ................................................................................................... 253 14.4.10 Runtime Semantics: EvaluateBody.......................................................................................... 253 14.4.11 Runtime Semantics: InstantiateFunctionObject ...................................................................... 253 14.4.12 Runtime Semantics: PropertyDefinitionEvaluation ................................................................ 254 14.4.13 Runtime Semantics: Evaluation .............................................................................................. 254 14.4.14

14.5 Class Definitions ....................................................................................................................... 256 Static Semantics: Early Errors................................................................................................. 256 14.5.1 Static Semantics: BoundNames .............................................................................................. 257 14.5.2 Static Semantics: ConstructorMethod .................................................................................... 257 14.5.3 Static Semantics: Contains...................................................................................................... 257 14.5.4 Static Semantics: ComputedPropertyContains ...................................................................... 258 14.5.5 Static Semantics: HasName ..................................................................................................... 258 14.5.6 Static Semantics: IsConstantDeclaration................................................................................ 258 14.5.7 Static Semantics: IsFunctionDefinition ................................................................................... 258 14.5.8 Static Semantics: IsStatic ........................................................................................................ 259 14.5.9

Static Semantics: NonConstructorMethodDefinitions ........................................................... 259 14.5.10 Static Semantics: PrototypePropertyNameList ...................................................................... 259 14.5.11 Static Semantics: PropName ................................................................................................... 259 14.5.12 Static Semantics: StaticPropertyNameList ............................................................................. 259 14.5.13 Runtime Semantics: ClassDefinitionEvaluation ...................................................................... 260 14.5.14 Runtime Semantics: BindingClassDeclarationEvaluation ...................................................... 261 14.5.15 Runtime Semantics: Evaluation .............................................................................................. 261 14.5.16

14.6 Tail Position Calls ..................................................................................................................... 262 Static Semantics: IsInTailPosition(nonterminal)...................................................................... 262 14.6.1 Static Semantics: HasProductionInTailPosition ...................................................................... 262 14.6.2 Runtime Semantics: PrepareForTailCall ( ) .............................................................................. 266 14.6.3

15 ECMAScript Language: Scripts and Modules .......................................................................... 266 15.1 Scripts........................................................................................................................................ 266

Static Semantics: Early Errors................................................................................................. 266 15.1.1 Static Semantics: IsStrict ......................................................................................................... 266 15.1.2 Static Semantics: LexicallyDeclaredNames ............................................................................ 266 15.1.3 Static Semantics: LexicallyScopedDeclarations .................................................................... 267 15.1.4 Static Semantics: VarDeclaredNames ..................................................................................... 267 15.1.5 Static Semantics: VarScopedDeclarations ............................................................................. 267 15.1.6 Runtime Semantics: ScriptEvaluation .................................................................................... 267 15.1.7 Runtime Semantics: GlobalDeclarationInstantiation (script, env) .......................................... 267 15.1.8 Runtime Semantics: ScriptEvaluationJob ( sourceText ) ........................................................ 269 15.1.9

15.2 Modules ..................................................................................................................................... 269 Module Semantics ..................................................................................................................... 269 15.2.1 Imports....................................................................................................................................... 282 15.2.2 Exports ...................................................................................................................................... 284 15.2.3

16 Error Handling and Language Extensions ............................................................................... 291 16.1 Forbidden Extensions ............................................................................................................... 291

17 ECMAScript Standard Built-in Objects ..................................................................................... 292

18 The Global Object ...................................................................................................................... 293 18.1 Value Properties of the Global Object ...................................................................................... 294

Infinity ........................................................................................................................................ 294 18.1.1 NaN ............................................................................................................................................ 294 18.1.2 undefined ................................................................................................................................... 294 18.1.3

18.2 Function Properties of the Global Object................................................................................. 294 eval (x) ....................................................................................................................................... 294 18.2.1 isFinite (number) ....................................................................................................................... 296 18.2.2 isNaN (number) ......................................................................................................................... 296 18.2.3 parseFloat (string) ..................................................................................................................... 297 18.2.4

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parseInt (string , radix) ............................................................................................................. 297 18.2.5 URI Handling Functions ............................................................................................................ 298 18.2.6

18.3 Constructor Properties of the Global Object ........................................................................... 302 Array ( . . . ) ................................................................................................................................ 302 18.3.1 ArrayBuffer ( . . . ) ...................................................................................................................... 302 18.3.2 Boolean ( . . . ) ........................................................................................................................... 302 18.3.3 DataView ( . . . ).......................................................................................................................... 302 18.3.4 Date ( . . . ) ................................................................................................................................. 303 18.3.5 Error ( . . . )................................................................................................................................. 303 18.3.6 EvalError ( . . . ) ......................................................................................................................... 303 18.3.7 Float32Array ( . . . ) .................................................................................................................... 303 18.3.8 Float64Array ( . . . ) .................................................................................................................... 303 18.3.9

Function ( . . . ) .......................................................................................................................... 303 18.3.10 Int8Array ( . . . ) .......................................................................................................................... 303 18.3.11 Int16Array ( . . . ) ........................................................................................................................ 303 18.3.12 Int32Array ( . . . ) ........................................................................................................................ 303 18.3.13 Map ( . . . ) .................................................................................................................................. 303 18.3.14 Number ( . . . ) ............................................................................................................................ 303 18.3.15 Object ( . . . ) .............................................................................................................................. 303 18.3.16 Proxy ( . . . ) ............................................................................................................................... 303 18.3.17 Promise ( . . . ) ........................................................................................................................... 303 18.3.18 RangeError ( . . . ) ...................................................................................................................... 303 18.3.19 ReferenceError ( . . . ) ................................................................................................................ 303 18.3.20 RegExp ( . . . ) ............................................................................................................................ 304 18.3.21 Set ( . . . ) .................................................................................................................................... 304 18.3.22 String ( . . . ) ............................................................................................................................... 304 18.3.23 Symbol ( . . . ) ............................................................................................................................ 304 18.3.24 SyntaxError ( . . . ) ..................................................................................................................... 304 18.3.25 TypeError ( . . . ) ........................................................................................................................ 304 18.3.26 Uint8Array ( . . . ) ....................................................................................................................... 304 18.3.27 Uint8ClampedArray ( . . . ) ......................................................................................................... 304 18.3.28 Uint16Array ( . . . ) ..................................................................................................................... 304 18.3.29 Uint32Array ( . . . ) ..................................................................................................................... 304 18.3.30 URIError ( . . . )........................................................................................................................... 304 18.3.31 WeakMap ( . . . ) ......................................................................................................................... 304 18.3.32 WeakSet ( . . . )........................................................................................................................... 304 18.3.33

18.4 Other Properties of the Global Object ...................................................................................... 304 JSON .......................................................................................................................................... 304 18.4.1 Math ........................................................................................................................................... 304 18.4.2 Reflect ....................................................................................................................................... 305 18.4.3

19 Fundamental Objects ................................................................................................................ 305 19.1 Object Objects........................................................................................................................... 305

The Object Constructor ............................................................................................................ 305 19.1.1 Properties of the Object Constructor ....................................................................................... 305 19.1.2 Properties of the Object Prototype Object ............................................................................... 309 19.1.3 Properties of Object Instances ................................................................................................. 310 19.1.4

19.2 Function Objects ....................................................................................................................... 311 The Function Constructor ........................................................................................................ 311 19.2.1 Properties of the Function Constructor ................................................................................... 312 19.2.2 Properties of the Function Prototype Object ........................................................................... 313 19.2.3 Function Instances ................................................................................................................... 315 19.2.4

19.3 Boolean Objects ........................................................................................................................ 316 The Boolean Constructor ......................................................................................................... 316 19.3.1 Properties of the Boolean Constructor .................................................................................... 316 19.3.2 Properties of the Boolean Prototype Object ............................................................................ 316 19.3.3 Properties of Boolean Instances .............................................................................................. 317 19.3.4

19.4 Symbol Objects ......................................................................................................................... 317 The Symbol Constructor........................................................................................................... 317 19.4.1 Properties of the Symbol Constructor ..................................................................................... 317 19.4.2

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Properties of the Symbol Prototype Object ............................................................................. 319 19.4.3 Properties of Symbol Instances ............................................................................................... 320 19.4.4

19.5 Error Objects ............................................................................................................................. 320 The Error Constructor ............................................................................................................... 321 19.5.1 Properties of the Error Constructor ......................................................................................... 321 19.5.2 Properties of the Error Prototype Object ................................................................................. 321 19.5.3 Properties of Error Instances ................................................................................................... 322 19.5.4 Native Error Types Used in This Standard ............................................................................... 322 19.5.5 NativeError Object Structure .................................................................................................... 322 19.5.6

20 Numbers and Dates ................................................................................................................... 324 20.1 Number Objects ........................................................................................................................ 324

The Number Constructor .......................................................................................................... 324 20.1.1 Properties of the Number Constructor ..................................................................................... 324 20.1.2 Properties of the Number Prototype Object ............................................................................. 326 20.1.3 Properties of Number Instances ............................................................................................... 330 20.1.4

20.2 The Math Object ........................................................................................................................ 330 Value Properties of the Math Object ......................................................................................... 331 20.2.1 Function Properties of the Math Object ................................................................................... 332 20.2.2

20.3 Date Objects .............................................................................................................................. 339 Overview of Date Objects and Definitions of Abstract Operations ......................................... 339 20.3.1 The Date Constructor ................................................................................................................ 344 20.3.2 Properties of the Date Constructor .......................................................................................... 346 20.3.3 Properties of the Date Prototype Object .................................................................................. 347 20.3.4 Properties of Date Instances .................................................................................................... 357 20.3.5

21 Text Processing ........................................................................................................................ 357 21.1 String Objects............................................................................................................................ 357

The String Constructor ............................................................................................................. 357 21.1.1 Properties of the String Constructor ........................................................................................ 357 21.1.2 Properties of the String Prototype Object ................................................................................ 359 21.1.3 Properties of String Instances .................................................................................................. 372 21.1.4 String Iterator Objects ............................................................