ECMA-262_6th_edition_june_2015

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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 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
 
iv © Ecma International 2015 
 
 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 7.3.11Call(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
 
© Ecma International 2015 v 
 
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
 
vi © Ecma International 2015 
 
 [[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 12.2.10
12.3 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 ( << ) .................................................................................................... 170 12.8.3
 The Signed Right 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 13.15.8
13.16 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 ( . . . ) ............................................................................................................................