Reference number ECMA-123:2009

© Ecma International 2009

Ecma/TC39/2015/30

ECMA-262 6th Edition / April 2015

Final draft

ECMAScript 2015

Language Specification

Report Errors and Issues at: https://bugs.ecmascript.org

Product: Draft for 6th Edition Component: choose an appropriate one Version: Rev 38, April 14, 2015 Final Draft

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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 .................................................................................................................................. 17 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 ...................................................................................................................................... 19 6.1.6 The Object Type ......................................................................................................................................... 20 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 )............................................................................................................................... 44 7.1.13 ToPropertyKey ( argument ) .................................................................................................................... 44 7.1.14 ToLength ( argument ) .............................................................................................................................. 44 7.1.15 CanonicalNumericIndexString ( argument ) ......................................................................................... 45 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 ) ...................................................................................................................... 46 7.2.4 IsExtensible (O) ......................................................................................................................................... 46 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) ................................................................................................................................. 47 7.2.10 Abstract Relational Comparison ............................................................................................................ 47 7.2.11 Abstract Equality Comparison ................................................................................................................ 48 7.2.12 Strict Equality Comparison .................................................................................................................. 49 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)................................................................................................................... 50 7.3.4 CreateMethodProperty (O, P, V) ............................................................................................................. 50 7.3.5 CreateDataPropertyOrThrow (O, P, V) ................................................................................................... 50 7.3.6 DefinePropertyOrThrow (O, P, desc) ..................................................................................................... 51 7.3.7 DeletePropertyOrThrow (O, P) ................................................................................................................ 51 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]) ....................................................................................................................... 52 7.3.12 Construct (F, [argumentsList], [newTarget]) ........................................................................................ 52 7.3.13 SetIntegrityLevel (O, level) ...................................................................................................................... 52 7.3.14 TestIntegrityLevel (O, level) .................................................................................................................... 53 7.3.15 CreateArrayFromList (elements) ............................................................................................................ 53 7.3.16 CreateListFromArrayLike (obj [, elementTypes] ) ............................................................................... 53 7.3.17 Invoke(O,P, [argumentsList]) .................................................................................................................. 54 7.3.18 OrdinaryHasInstance (C, O) .................................................................................................................... 54 7.3.19 SpeciesConstructor ( O, defaultConstructor ) ..................................................................................... 54 7.3.20 EnumerableOwnNames (O) ..................................................................................................................... 54 7.3.21 GetFunctionRealm ( obj ) ......................................................................................................................... 55 7.3.22

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

8 Executable Code and Execution Contexts ........................................................................................... 57 8.1 Lexical Environments ............................................................................................................................... 57

Environment Records............................................................................................................................... 58 8.1.1 Lexical Environment Operations ............................................................................................................ 72 8.1.2

8.2 Code Realms .............................................................................................................................................. 74 CreateRealm ( ) .......................................................................................................................................... 74 8.2.1 CreateIntrinsics ( realmRec )................................................................................................................... 74 8.2.2 SetRealmGlobalObject ( realmRec, globalObj ) ................................................................................... 75 8.2.3 SetDefaultGlobalBindings ( realmRec ) ................................................................................................ 75 8.2.4

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8.3 Execution Contexts ................................................................................................................................... 75 ResolveBinding ( name, [env] ) ............................................................................................................... 77 8.3.1 GetThisEnvironment ( ) ............................................................................................................................ 77 8.3.2 ResolveThisBinding ( ) ............................................................................................................................. 77 8.3.3 GetNewTarget ( ) ........................................................................................................................................ 77 8.3.4 GetGlobalObject ( ).................................................................................................................................... 77 8.3.5

8.4 Jobs and Job Queues ............................................................................................................................... 78 EnqueueJob (queueName, job, arguments) ......................................................................................... 79 8.4.1 NextJob result ............................................................................................................................................ 79 8.4.2

8.5 ECMAScript Initialization() ....................................................................................................................... 79 InitializeHostDefinedRealm ( realm ) ...................................................................................................... 80 8.5.1

9 Ordinary and Exotic Objects Behaviours ............................................................................................. 80 9.1 Ordinary Object Internal Methods and Internal Slots ......................................................................... 80

[[GetPrototypeOf]] ( ) ................................................................................................................................ 80 9.1.1 [[SetPrototypeOf]] (V) ............................................................................................................................... 80 9.1.2 [[IsExtensible]] ( ) ...................................................................................................................................... 81 9.1.3 [[PreventExtensions]] ( ) .......................................................................................................................... 81 9.1.4 [[GetOwnProperty]] (P) ............................................................................................................................. 81 9.1.5 [[DefineOwnProperty]] (P, Desc) ............................................................................................................ 81 9.1.6 [[HasProperty]](P) ..................................................................................................................................... 83 9.1.7 [[Get]] (P, Receiver) ................................................................................................................................... 83 9.1.8 [[Set]] ( P, V, Receiver) ............................................................................................................................. 83 9.1.9

[[Delete]] (P)................................................................................................................................................ 84 9.1.10 [[Enumerate]] () .......................................................................................................................................... 84 9.1.11 [[OwnPropertyKeys]] ( )............................................................................................................................ 85 9.1.12 ObjectCreate(proto, internalSlotsList) .............................................................................................. 85 9.1.13 OrdinaryCreateFromConstructor ( constructor, intrinsicDefaultProto, internalSlotsList ) ........ 85 9.1.14 GetPrototypeFromConstructor ( constructor, intrinsicDefaultProto ) ............................................. 86 9.1.15

9.2 ECMAScript Function Objects ................................................................................................................ 86 [[Call]] ( thisArgument, argumentsList) ................................................................................................. 87 9.2.1 [[Construct]] ( argumentsList, newTarget) ........................................................................................... 88 9.2.2 FunctionAllocate (functionPrototype, strict [,functionKind] ) ........................................................... 89 9.2.3 FunctionInitialize (F, kind, ParameterList, Body, Scope) ................................................................... 89 9.2.4 FunctionCreate (kind, ParameterList, Body, Scope, Strict, prototype) ........................................... 90 9.2.5 GeneratorFunctionCreate (kind, ParameterList, Body, Scope, Strict) ............................................. 90 9.2.6 AddRestrictedFunctionProperties ( F, realm ) ..................................................................................... 90 9.2.7 MakeConstructor (F, writablePrototype, prototype) ........................................................................... 90 9.2.8 MakeClassConstructor ( F) ...................................................................................................................... 91 9.2.9

MakeMethod ( F, homeObject) ................................................................................................................ 91 9.2.10 SetFunctionName (F, name, prefix) ........................................................................................................ 91 9.2.11 FunctionDeclarationInstantiation(func, argumentsList) .................................................................... 91 9.2.12

9.3 Built-in Function Objects ......................................................................................................................... 94 [[Call]] ( thisArgument, argumentsList) ................................................................................................. 95 9.3.1 [[Construct]] (argumentsList, newTarget) ............................................................................................ 95 9.3.2 CreateBuiltinFunction(realm, steps, prototype, internalSlotsList)................................................... 95 9.3.3

9.4 Built-in Exotic Object Internal Methods and Slots .............................................................................. 95 Bound Function Exotic Objects .............................................................................................................. 96 9.4.1 Array Exotic Objects ................................................................................................................................. 97 9.4.2 String Exotic Objects ................................................................................................................................ 99 9.4.3 Arguments Exotic Objects ..................................................................................................................... 101 9.4.4 Integer Indexed Exotic Objects ............................................................................................................. 105 9.4.5 Module Namespace Exotic Objects ..................................................................................................... 108 9.4.6

9.5 Proxy Object Internal Methods and Internal Slots............................................................................. 110 [[GetPrototypeOf]] ( ) .............................................................................................................................. 111 9.5.1 [[SetPrototypeOf]] (V) ............................................................................................................................. 112 9.5.2 [[IsExtensible]] ( ) .................................................................................................................................... 112 9.5.3 [[PreventExtensions]] ( ) ........................................................................................................................ 113 9.5.4 [[GetOwnProperty]] (P) ........................................................................................................................... 113 9.5.5 [[DefineOwnProperty]] (P, Desc) .......................................................................................................... 114 9.5.6

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[[HasProperty]] (P) .................................................................................................................................. 114 9.5.7 [[Get]] (P, Receiver)................................................................................................................................. 115 9.5.8 [[Set]] ( P, V, Receiver) ........................................................................................................................... 116 9.5.9

[[Delete]] (P) ............................................................................................................................................. 116 9.5.10 [[Enumerate]] () ........................................................................................................................................ 117 9.5.11 [[OwnPropertyKeys]] ( ) ......................................................................................................................... 117 9.5.12 [[Call]] (thisArgument, argumentsList)................................................................................................ 118 9.5.13 [[Construct]] ( argumentsList, newTarget) ......................................................................................... 118 9.5.14 ProxyCreate(target, handler) ................................................................................................................. 118 9.5.15

10 ECMAScript Language: Source Code ................................................................................................. 119 10.1 Source Text .............................................................................................................................................. 119

Static Semantics: UTF16Encoding ( cp ) ........................................................................................... 119 10.1.1 Static Semantics: UTF16Decode( lead, trail ) ..................................................................................... 120 10.1.2

10.2 Types of Source Code ............................................................................................................................ 120 Strict Mode Code ..................................................................................................................................... 120 10.2.1 Non-ECMAScript Functions .................................................................................................................. 121 10.2.2

11 ECMAScript Language: Lexical Grammar .......................................................................................... 121 11.1 Unicode Format-Control Characters.................................................................................................... 122 11.2 White Space ............................................................................................................................................. 122 11.3 Line Terminators ..................................................................................................................................... 123 11.4 Comments ................................................................................................................................................ 124 11.5 Tokens ....................................................................................................................................................... 125 11.6 Names and Keywords............................................................................................................................. 125

Identifier Names ...................................................................................................................................... 126 11.6.1 Reserved Words ...................................................................................................................................... 126 11.6.2

11.7 Punctuators .............................................................................................................................................. 127 11.8 Literals ...................................................................................................................................................... 128

Null Literals .............................................................................................................................................. 128 11.8.1 Boolean Literals ...................................................................................................................................... 128 11.8.2 Numeric Literals ...................................................................................................................................... 128 11.8.3 String Literals .......................................................................................................................................... 131 11.8.4 Regular Expression Literals .................................................................................................................. 133 11.8.5 Template Literal Lexical Components ................................................................................................. 135 11.8.6

11.9 Automatic Semicolon Insertion ............................................................................................................ 137 Rules of Automatic Semicolon Insertion ............................................................................................ 137 11.9.1 Examples of Automatic Semicolon Insertion ..................................................................................... 138 11.9.2

12 ECMAScript Language: Expressions .................................................................................................. 140 12.1 Identifiers .................................................................................................................................................. 140

Static Semantics: Early Errors............................................................................................................. 140 12.1.1 Static Semantics: BoundNames ........................................................................................................... 140 12.1.2 Static Semantics: IsValidSimpleAssignmentTarget ........................................................................ 141 12.1.3 Static Semantics: StringValue ............................................................................................................... 141 12.1.4 Runtime Semantics: BindingInitialization .......................................................................................... 141 12.1.5 Runtime Semantics: Evaluation .......................................................................................................... 142 12.1.6

12.2 Primary Expression ................................................................................................................................ 142 Semantics ................................................................................................................................................. 142 12.2.1 The this Keyword .................................................................................................................................. 144 12.2.2 Identifier Reference................................................................................................................................. 144 12.2.3 Literals ...................................................................................................................................................... 144 12.2.4 Array Initializer......................................................................................................................................... 145 12.2.5 Object Initializer ....................................................................................................................................... 147 12.2.6 Function Defining Expressions ............................................................................................................ 151 12.2.7 Regular Expression Literals .................................................................................................................. 151 12.2.8 Template Literals ..................................................................................................................................... 151 12.2.9

The Grouping Operator .......................................................................................................................... 155 12.2.1012.3 Left-Hand-Side Expressions ................................................................................................................. 156

Static Semantics ...................................................................................................................................... 157 12.3.1 Property Accessors ................................................................................................................................ 159 12.3.2

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The new Operator .................................................................................................................................... 160 12.3.3 Function Calls .......................................................................................................................................... 160 12.3.4 The super Keyword ................................................................................................................................ 162 12.3.5 Argument Lists ........................................................................................................................................ 163 12.3.6 Tagged Templates ................................................................................................................................... 164 12.3.7 Meta Properties ........................................................................................................................................ 164 12.3.8

12.4 Postfix Expressions ................................................................................................................................ 164 Static Semantics: Early Errors ............................................................................................................. 164 12.4.1 Static Semantics: IsFunctionDefinition .............................................................................................. 164 12.4.2 Static Semantics: IsValidSimpleAssignmentTarget......................................................................... 164 12.4.3 Postfix Increment Operator ................................................................................................................... 165 12.4.4 Postfix Decrement Operator .................................................................................................................. 165 12.4.5

12.5 Unary Operators ...................................................................................................................................... 165 Static Semantics: Early Errors ............................................................................................................. 165 12.5.1 Static Semantics: IsFunctionDefinition .............................................................................................. 166 12.5.2 Static Semantics: IsValidSimpleAssignmentTarget......................................................................... 166 12.5.3 The delete Operator .............................................................................................................................. 166 12.5.4 The void Operator .................................................................................................................................. 167 12.5.5 The typeof Operator .............................................................................................................................. 167 12.5.6 Prefix Increment Operator ..................................................................................................................... 168 12.5.7 Prefix Decrement Operator .................................................................................................................... 168 12.5.8 Unary + Operator ..................................................................................................................................... 168 12.5.9

Unary - Operator ..................................................................................................................................... 169 12.5.10 Bitwise NOT Operator ( ~ ) ..................................................................................................................... 169 12.5.11 Logical NOT Operator ( ! ) ..................................................................................................................... 169 12.5.12

12.6 Multiplicative Operators ......................................................................................................................... 169 Static Semantics: IsFunctionDefinition .............................................................................................. 169 12.6.1 Static Semantics: IsValidSimpleAssignmentTarget......................................................................... 170 12.6.2 Runtime Semantics: Evaluation .......................................................................................................... 170 12.6.3

12.7 Additive Operators .................................................................................................................................. 172 Static Semantics: IsFunctionDefinition .............................................................................................. 172 12.7.1 Static Semantics: IsValidSimpleAssignmentTarget......................................................................... 172 12.7.2 The Addition operator ( + )..................................................................................................................... 172 12.7.3 The Subtraction Operator ( - ) .............................................................................................................. 173 12.7.4 Applying the Additive Operators to Numbers .................................................................................... 173 12.7.5

12.8 Bitwise Shift Operators .......................................................................................................................... 174 Static Semantics: IsFunctionDefinition .............................................................................................. 174 12.8.1 Static Semantics: IsValidSimpleAssignmentTarget......................................................................... 174 12.8.2 The Left Shift Operator ( > ) ................................................................................................ 174 12.8.4 The Unsigned Right Shift Operator ( >>> ) ......................................................................................... 175 12.8.5

12.9 Relational Operators ............................................................................................................................... 175 Static Semantics: IsFunctionDefinition .............................................................................................. 176 12.9.1 Static Semantics: IsValidSimpleAssignmentTarget......................................................................... 176 12.9.2 Runtime Semantics: Evaluation .......................................................................................................... 176 12.9.3 Runtime Semantics: InstanceofOperator(O, C) ................................................................................. 177 12.9.4

12.10 Equality Operators .................................................................................................................................. 177 Static Semantics: IsFunctionDefinition .............................................................................................. 178 12.10.1 Static Semantics: IsValidSimpleAssignmentTarget......................................................................... 178 12.10.2 Runtime Semantics: Evaluation .......................................................................................................... 178 12.10.3

12.11 Binary Bitwise Operators ....................................................................................................................... 179 Static Semantics: IsFunctionDefinition .............................................................................................. 179 12.11.1 Static Semantics: IsValidSimpleAssignmentTarget......................................................................... 180 12.11.2 Runtime Semantics: Evaluation .......................................................................................................... 180 12.11.3

12.12 Binary Logical Operators ....................................................................................................................... 180 Static Semantics: IsFunctionDefinition .............................................................................................. 180 12.12.1 Static Semantics: IsValidSimpleAssignmentTarget......................................................................... 181 12.12.2 Runtime Semantics: Evaluation .......................................................................................................... 181 12.12.3

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12.13 Conditional Operator ( ? : ) .............................................................................................................. 181 Static Semantics: IsFunctionDefinition .............................................................................................. 181 12.13.1 Static Semantics: IsValidSimpleAssignmentTarget ........................................................................ 181 12.13.2 Runtime Semantics: Evaluation .......................................................................................................... 182 12.13.3

12.14 Assignment Operators ........................................................................................................................... 182 Static Semantics: Early Errors............................................................................................................. 182 12.14.1 Static Semantics: IsFunctionDefinition .............................................................................................. 182 12.14.2 Static Semantics: IsValidSimpleAssignmentTarget ........................................................................ 182 12.14.3 Runtime Semantics: Evaluation .......................................................................................................... 183 12.14.4 Destructuring Assignment .................................................................................................................... 183 12.14.5

12.15 Comma Operator ( , ) .......................................................................................................................... 189 Static Semantics: IsFunctionDefinition .............................................................................................. 189 12.15.1 Static Semantics: IsValidSimpleAssignmentTarget ........................................................................ 189 12.15.2 Runtime Semantics: Evaluation .......................................................................................................... 189 12.15.3

13 ECMAScript Language: Statements and Declarations ..................................................................... 189 13.1 Statement Semantics .............................................................................................................................. 190

Static Semantics: ContainsDuplicateLabels ...................................................................................... 190 13.1.1 Static Semantics: ContainsUndefinedBreakTarget .......................................................................... 190 13.1.2 Static Semantics: ContainsUndefinedContinueTarget..................................................................... 190 13.1.3 Static Semantics: DeclarationPart ...................................................................................................... 191 13.1.4 Static Semantics: VarDeclaredNames ................................................................................................ 191 13.1.5 Static Semantics: VarScopedDeclarations ........................................................................................ 191 13.1.6 Runtime Semantics: LabelledEvaluation .......................................................................................... 192 13.1.7 Runtime Semantics: Evaluation .......................................................................................................... 192 13.1.8

13.2 Block .......................................................................................................................................................... 192 Static Semantics: Early Errors............................................................................................................. 193 13.2.1 Static Semantics: ContainsDuplicateLabels ...................................................................................... 193 13.2.2 Static Semantics: ContainsUndefinedBreakTarget .......................................................................... 193 13.2.3 Static Semantics: ContainsUndefinedContinueTarget..................................................................... 193 13.2.4 Static Semantics: LexicallyDeclaredNames ...................................................................................... 194 13.2.5 Static Semantics: LexicallyScopedDeclarations .............................................................................. 194 13.2.6 Static Semantics: TopLevelLexicallyDeclaredNames ..................................................................... 194 13.2.7 Static Semantics: TopLevelLexicallyScopedDeclarations ............................................................. 195 13.2.8 Static Semantics: TopLevelVarDeclaredNames ............................................................................... 195 13.2.9

Static Semantics: TopLevelVarScopedDeclarations ....................................................................... 196 13.2.10 Static Semantics: VarDeclaredNames ................................................................................................ 196 13.2.11 Static Semantics: VarScopedDeclarations ........................................................................................ 196 13.2.12 Runtime Semantics: Evaluation .......................................................................................................... 197 13.2.13 Runtime Semantics: BlockDeclarationInstantiation( code, env ) ................................................... 197 13.2.14

13.3 Declarations and the Variable Statement............................................................................................ 198 Let and Const Declarations ................................................................................................................... 198 13.3.1 Variable Statement .................................................................................................................................. 200 13.3.2 Destructuring Binding Patterns ............................................................................................................ 201 13.3.3

13.4 Empty Statement ..................................................................................................................................... 208 Runtime Semantics: Evaluation .......................................................................................................... 208 13.4.1

13.5 Expression Statement ............................................................................................................................ 209 Runtime Semantics: Evaluation .......................................................................................................... 209 13.5.1

13.6 The if Statement .................................................................................................................................... 209 Static Semantics: Early Errors............................................................................................................. 209 13.6.1 Static Semantics: ContainsDuplicateLabels ...................................................................................... 209 13.6.2 Static Semantics: ContainsUndefinedBreakTarget .......................................................................... 209 13.6.3 Static Semantics: ContainsUndefinedContinueTarget..................................................................... 210 13.6.4 Static Semantics: VarDeclaredNames ................................................................................................ 210 13.6.5 Static Semantics: VarScopedDeclarations ........................................................................................ 210 13.6.6 Runtime Semantics: Evaluation ......................................................................................................... 211 13.6.7

13.7 Iteration Statements................................................................................................................................ 211 Semantics ................................................................................................................................................. 211 13.7.1 The do-while Statement ........................................................................................................................ 212 13.7.2

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The while Statement.............................................................................................................................. 213 13.7.3 The for Statement .................................................................................................................................. 214 13.7.4 The for-in and for-of Statements ..................................................................................................... 217 13.7.5

13.8 The continue Statement ....................................................................................................................... 223 Static Semantics: Early Errors ............................................................................................................. 223 13.8.1 Static Semantics: ContainsUndefinedContinueTarget ..................................................................... 223 13.8.2 Runtime Semantics: Evaluation .......................................................................................................... 223 13.8.3

13.9 The break Statement.............................................................................................................................. 224 Static Semantics: Early Errors ............................................................................................................. 224 13.9.1 Static Semantics: ContainsUndefinedBreakTarget ........................................................................... 224 13.9.2 Runtime Semantics: Evaluation .......................................................................................................... 224 13.9.3

13.10 The return Statement ........................................................................................................................... 224 Runtime Semantics: Evaluation .......................................................................................................... 224 13.10.1

13.11 The with Statement ................................................................................................................................ 225 Static Semantics: Early Errors ............................................................................................................. 225 13.11.1 Static Semantics: ContainsDuplicateLabels ...................................................................................... 225 13.11.2 Static Semantics: ContainsUndefinedBreakTarget ........................................................................... 225 13.11.3 Static Semantics: ContainsUndefinedContinueTarget ..................................................................... 225 13.11.4 Static Semantics: VarDeclaredNames ................................................................................................ 225 13.11.5 Static Semantics: VarScopedDeclarations ........................................................................................ 226 13.11.6 Runtime Semantics: Evaluation .......................................................................................................... 226 13.11.7

13.12 The switch Statement ........................................................................................................................... 226 Static Semantics: Early Errors ............................................................................................................. 226 13.12.1 Static Semantics: ContainsDuplicateLabels ...................................................................................... 227 13.12.2 Static Semantics: ContainsUndefinedBreakTarget ........................................................................... 227 13.12.3 Static Semantics: ContainsUndefinedContinueTarget ..................................................................... 228 13.12.4 Static Semantics: LexicallyDeclaredNames ...................................................................................... 229 13.12.5 Static Semantics: LexicallyScopedDeclarations .............................................................................. 229 13.12.6 Static Semantics: VarDeclaredNames ................................................................................................ 230 13.12.7 Static Semantics: VarScopedDeclarations ........................................................................................ 230 13.12.8 Runtime Semantics: CaseBlockEvaluation ....................................................................................... 231 13.12.9

Runtime Semantics: CaseSelectorEvaluation .......................................................................... 232 13.12.10 Runtime Semantics: Evaluation .................................................................................................. 232 13.12.11

13.13 Labelled Statements ............................................................................................................................... 233 Static Semantics: Early Errors ............................................................................................................. 233 13.13.1 Static Semantics: ContainsDuplicateLabels ...................................................................................... 233 13.13.2 Static Semantics: ContainsUndefinedBreakTarget ........................................................................... 233 13.13.3 Static Semantics: ContainsUndefinedContinueTarget ..................................................................... 234 13.13.4 Static Semantics: IsLabelledFunction ( stmt ) .................................................................................. 234 13.13.5 Static Semantics: LexicallyDeclaredNames ...................................................................................... 234 13.13.6 Static Semantics: LexicallyScopedDeclarations .............................................................................. 234 13.13.7 Static Semantics: TopLevelLexicallyDeclaredNames ..................................................................... 235 13.13.8 Static Semantics: TopLevelLexicallyScopedDeclarations ............................................................. 235 13.13.9

Static Semantics: TopLevelVarDeclaredNames ....................................................................... 235 13.13.10 Static Semantics: TopLevelVarScopedDeclarations ............................................................... 235 13.13.11 Static Semantics: VarDeclaredNames ........................................................................................ 236 13.13.12 Static Semantics: VarScopedDeclarations ................................................................................ 236 13.13.13 Runtime Semantics: LabelledEvaluation .................................................................................. 236 13.13.14 Runtime Semantics: Evaluation ................................................................................................... 236 13.13.15

13.14 The throw Statement.............................................................................................................................. 237 Runtime Semantics: Evaluation .......................................................................................................... 237 13.14.1

13.15 The try Statement .................................................................................................................................. 237 Static Semantics: Early Errors ............................................................................................................. 237 13.15.1 Static Semantics: ContainsDuplicateLabels ...................................................................................... 237 13.15.2 Static Semantics: ContainsUndefinedBreakTarget ........................................................................... 238 13.15.3 Static Semantics: ContainsUndefinedContinueTarget ..................................................................... 238 13.15.4 Static Semantics: VarDeclaredNames ................................................................................................ 239 13.15.5 Static Semantics: VarScopedDeclarations ........................................................................................ 239 13.15.6 Runtime Semantics: CatchClauseEvaluation..................................................................................... 240 13.15.7

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Runtime Semantics: Evaluation .......................................................................................................... 240 13.15.813.16 The debugger statement ....................................................................................................................... 241

Runtime Semantics: Evaluation .......................................................................................................... 241 13.16.1

14 ECMAScript Language: Functions and Classes................................................................................ 241 14.1 Function Definitions ............................................................................................................................... 241

Directive Prologues and the Use Strict Directive .............................................................................. 242 14.1.1 Static Semantics: Early Errors............................................................................................................. 242 14.1.2 Static Semantics: BoundNames .......................................................................................................... 243 14.1.3 Static Semantics: Contains .................................................................................................................. 243 14.1.4 Static Semantics: ContainsExpression .............................................................................................. 244 14.1.5 Static Semantics: ExpectedArgumentCount..................................................................................... 244 14.1.6 Static Semantics: HasInitializer ........................................................................................................... 244 14.1.7 Static Semantics: HasName ................................................................................................................. 245 14.1.8 Static Semantics: IsAnonymousFunctionDefinition ( production ) .............................................. 245 14.1.9

Static Semantics: IsConstantDeclaration .......................................................................................... 245 14.1.10 Static Semantics: IsFunctionDefinition .............................................................................................. 245 14.1.11 Static Semantics: IsSimpleParameterList ......................................................................................... 245 14.1.12 Static Semantics: LexicallyDeclaredNames ...................................................................................... 246 14.1.13 Static Semantics: LexicallyScopedDeclarations .............................................................................. 246 14.1.14 Static Semantics: VarDeclaredNames ................................................................................................ 246 14.1.15 Static Semantics: VarScopedDeclarations ........................................................................................ 246 14.1.16 Runtime Semantics: EvaluateBody ..................................................................................................... 247 14.1.17 Runtime Semantics: IteratorBindingInitialization ........................................................................... 247 14.1.18 Runtime Semantics: InstantiateFunctionObject ................................................................................ 248 14.1.19 Runtime Semantics: Evaluation .......................................................................................................... 248 14.1.20

14.2 Arrow Function Definitions ................................................................................................................... 249 Static Semantics: Early Errors............................................................................................................. 249 14.2.1 Static Semantics: BoundNames .......................................................................................................... 250 14.2.2 Static Semantics: Contains .................................................................................................................. 250 14.2.3 Static Semantics: ContainsExpression .............................................................................................. 250 14.2.4 Static Semantics: ExpectedArgumentCount..................................................................................... 250 14.2.5 Static Semantics: HasInitializer ........................................................................................................... 250 14.2.6 Static Semantics: HasName ................................................................................................................. 251 14.2.7 Static Semantics: IsSimpleParameterList ......................................................................................... 251 14.2.8 Static Semantics: CoveredFormalsList .............................................................................................. 251 14.2.9

Static Semantics: LexicallyDeclaredNames ...................................................................................... 251 14.2.10 Static Semantics: LexicallyScopedDeclarations .............................................................................. 251 14.2.11 Static Semantics: VarDeclaredNames ................................................................................................ 252 14.2.12 Static Semantics: VarScopedDeclarations ........................................................................................ 252 14.2.13 Runtime Semantics: IteratorBindingInitialization ........................................................................... 252 14.2.14 Runtime Semantics: EvaluateBody ..................................................................................................... 252 14.2.15 Runtime Semantics: Evaluation .......................................................................................................... 253 14.2.16

14.3 Method Definitions .................................................................................................................................. 253 Static Semantics: Early Errors............................................................................................................. 253 14.3.1 Static Semantics: ComputedPropertyContains ................................................................................ 253 14.3.2 Static Semantics: ExpectedArgumentCount..................................................................................... 253 14.3.3 Static Semantics: HasComputedPropertyKey .................................................................................. 254 14.3.4 Static Semantics: HasDirectSuper ...................................................................................................... 254 14.3.5 Static Semantics: PropName ............................................................................................................... 254 14.3.6 Static Semantics: SpecialMethod........................................................................................................ 254 14.3.7 Runtime Semantics: DefineMethod ..................................................................................................... 254 14.3.8 Runtime Semantics: PropertyDefinitionEvaluation ......................................................................... 255 14.3.9

14.4 Generator Function Definitions ............................................................................................................ 256 Static Semantics: Early Errors............................................................................................................. 256 14.4.1 Static Semantics: BoundNames .......................................................................................................... 256 14.4.2 Static Semantics: ComputedPropertyContains ................................................................................ 257 14.4.3 Static Semantics: Contains .................................................................................................................. 257 14.4.4 Static Semantics: HasComputedPropertyKey .................................................................................. 257 14.4.5 Static Semantics: HasDirectSuper ...................................................................................................... 257 14.4.6

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Static Semantics: HasName ................................................................................................................. 258 14.4.7 Static Semantics: IsConstantDeclaration .......................................................................................... 258 14.4.8 Static Semantics: IsFunctionDefinition .............................................................................................. 258 14.4.9

Static Semantics: PropName ............................................................................................................... 258 14.4.10 Runtime Semantics: EvaluateBody ..................................................................................................... 258 14.4.11 Runtime Semantics: InstantiateFunctionObject ................................................................................ 259 14.4.12 Runtime Semantics: PropertyDefinitionEvaluation ......................................................................... 259 14.4.13 Runtime Semantics: Evaluation .......................................................................................................... 259 14.4.14

14.5 Class Definitions ..................................................................................................................................... 261 Static Semantics: Early Errors ............................................................................................................. 262 14.5.1 Static Semantics: BoundNames .......................................................................................................... 262 14.5.2 Static Semantics: ConstructorMethod ............................................................................................... 262 14.5.3 Static Semantics: Contains .................................................................................................................. 263 14.5.4 Static Semantics: ComputedPropertyContains ................................................................................ 263 14.5.5 Static Semantics: HasName ................................................................................................................. 263 14.5.6 Static Semantics: IsConstantDeclaration .......................................................................................... 263 14.5.7 Static Semantics: IsFunctionDefinition .............................................................................................. 264 14.5.8 Static Semantics: IsStatic ..................................................................................................................... 264 14.5.9

Static Semantics: NonConstructorMethodDefinitions .................................................................... 264 14.5.10 Static Semantics: PrototypePropertyNameList ................................................................................ 264 14.5.11 Static Semantics: PropName ............................................................................................................... 264 14.5.12 Static Semantics: StaticPropertyNameList ....................................................................................... 265 14.5.13 Runtime Semantics: ClassDefinitionEvaluation ................................................................................ 265 14.5.14 Runtime Semantics: BindingClassDeclarationEvaluation ............................................................... 266 14.5.15 Runtime Semantics: Evaluation .......................................................................................................... 266 14.5.16

14.6 Tail Position Calls ................................................................................................................................... 267 Static Semantics: IsInTailPosition(nonterminal) ............................................................................... 267 14.6.1 Static Semantics: HasProductionInTailPosition ................................................................................ 267 14.6.2 Runtime Semantics: PrepareForTailCall ( ) ...................................................................................... 271 14.6.3

15 ECMAScript Language: Scripts and Modules .................................................................................... 271 15.1 Scripts ....................................................................................................................................................... 271

Static Semantics: Early Errors ............................................................................................................. 271 15.1.1 Static Semantics: IsStrict...................................................................................................................... 272 15.1.2 Static Semantics: LexicallyDeclaredNames ...................................................................................... 272 15.1.3 Static Semantics: LexicallyScopedDeclarations .............................................................................. 272 15.1.4 Static Semantics: VarDeclaredNames ................................................................................................ 272 15.1.5 Static Semantics: VarScopedDeclarations ........................................................................................ 272 15.1.6 Runtime Semantics: ScriptEvaluation ............................................................................................... 272 15.1.7 Runtime Semantics: GlobalDeclarationInstantiation (script, env) ................................................. 273 15.1.8 Runtime Semantics: ScriptEvaluationJob ( sourceText ) ................................................................ 274 15.1.9

15.2 Modules ..................................................................................................................................................... 275 Module Semantics ................................................................................................................................... 275 15.2.1 Imports ...................................................................................................................................................... 287 15.2.2 Exports ...................................................................................................................................................... 290 15.2.3

16 Error Handling and Language Extensions .......................................................................................... 296 16.1 Forbidden Extensions ............................................................................................................................ 297

17 ECMAScript Standard Built-in Objects ................................................................................................ 298

18 The Global Object .................................................................................................................................... 299 18.1 Value Properties of the Global Object ................................................................................................. 299

Infinity ........................................................................................................................................................ 299 18.1.1 NaN............................................................................................................................................................. 299 18.1.2 undefined .................................................................................................................................................. 299 18.1.3

18.2 Function Properties of the Global Object ........................................................................................... 300 eval (x) ....................................................................................................................................................... 300 18.2.1 isFinite (number) ..................................................................................................................................... 302 18.2.2 isNaN (number) ........................................................................................................................................ 302 18.2.3 parseFloat (string) ................................................................................................................................... 302 18.2.4

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parseInt (string , radix) ........................................................................................................................... 303 18.2.5 URI Handling Functions ......................................................................................................................... 304 18.2.6

18.3 Constructor Properties of the Global Object ..................................................................................... 308 Array ( . . . ) ............................................................................................................................................... 308 18.3.1 ArrayBuffer ( . . . ) .................................................................................................................................... 308 18.3.2 Boolean ( . . . ) .......................................................................................................................................... 308 18.3.3 DataView ( . . . ) ........................................................................................................................................ 308 18.3.4 Date ( . . . ) ................................................................................................................................................. 308 18.3.5 Error ( . . . ) ................................................................................................................................................ 309 18.3.6 EvalError ( . . . ) ........................................................................................................................................ 309 18.3.7 Float32Array ( . . . ) .................................................................................................................................. 309 18.3.8 Float64Array ( . . . ) .................................................................................................................................. 309 18.3.9

Function ( . . . ) ......................................................................................................................................... 309 18.3.10 Int8Array ( . . . ) ........................................................................................................................................ 309 18.3.11 Int16Array ( . . . ) ...................................................................................................................................... 309 18.3.12 Int32Array ( . . . ) ...................................................................................................................................... 309 18.3.13 Map ( . . . ) ................................................................................................................................................. 309 18.3.14 Number ( . . . ) ........................................................................................................................................... 309 18.3.15 Object ( . . . ) ............................................................................................................................................. 309 18.3.16 Proxy ( . . . ) .............................................................................................................................................. 309 18.3.17 Promise ( . . . ) .......................................................................................................................................... 309 18.3.18 RangeError ( . . . ) .................................................................................................................................... 309 18.3.19 ReferenceError ( . . . ) ............................................................................................................................. 309 18.3.20 RegExp ( . . . ) ........................................................................................................................................... 310 18.3.21 Set ( . . . ) ................................................................................................................................................... 310 18.3.22 String ( . . . ) .............................................................................................................................................. 310 18.3.23 Symbol ( . . . ) ........................................................................................................................................... 310 18.3.24 SyntaxError ( . . . ) ................................................................................................................................... 310 18.3.25 TypeError ( . . . ) ....................................................................................................................................... 310 18.3.26 Uint8Array ( . . . ) ...................................................................................................................................... 310 18.3.27 Uint8ClampedArray ( . . . ) ...................................................................................................................... 310 18.3.28 Uint16Array ( . . . ) ................................................................................................................................... 310 18.3.29 Uint32Array ( . . . ) ................................................................................................................................... 310 18.3.30 URIError ( . . . ) ......................................................................................................................................... 310 18.3.31 WeakMap ( . . . )........................................................................................................................................ 310 18.3.32 WeakSet ( . . . ) ......................................................................................................................................... 310 18.3.33

18.4 Other Properties of the Global Object ................................................................................................. 310 JSON .......................................................................................................................................................... 310 18.4.1 Math ........................................................................................................................................................... 311 18.4.2 Reflect ....................................................................................................................................................... 311 18.4.3

19 Fundamental Objects ..............