Reference number ECMA-123:2009

Ecma International 2009

ECMA-262 8th Edition / June 2017

ECMAScript 2017 Language Specification

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Ecma International 2017

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Ecma International 2017 i

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ii Ecma International 2017

Introduction1Scope2Conformance3NormativeReferences4Overview4.1WebScripting4.2ECMAScriptOverview4.2.1Objects4.2.2TheStrictVariantofECMAScript

4.3TermsandDeinitions4.3.1type4.3.2primitivevalue4.3.3object4.3.4constructor4.3.5prototype4.3.6ordinaryobject4.3.7exoticobject4.3.8standardobject4.3.9builtinobject4.3.10undeinedvalue4.3.11Undeinedtype4.3.12nullvalue4.3.13Nulltype4.3.14Booleanvalue4.3.15Booleantype4.3.16Booleanobject4.3.17Stringvalue4.3.18Stringtype4.3.19Stringobject4.3.20Numbervalue4.3.21Numbertype4.3.22Numberobject4.3.23Ininity

ECMAScript2017LanguageSpeciicationTableofContents

4.3.24NaN4.3.25Symbolvalue4.3.26Symboltype4.3.27Symbolobject4.3.28function4.3.29builtinfunction4.3.30property4.3.31method4.3.32builtinmethod4.3.33attribute4.3.34ownproperty4.3.35inheritedproperty

4.4OrganizationofThisSpeciication5NotationalConventions5.1SyntacticandLexicalGrammars5.1.1ContextFreeGrammars5.1.2TheLexicalandRegExpGrammars5.1.3TheNumericStringGrammar5.1.4TheSyntacticGrammar5.1.5GrammarNotation

5.2AlgorithmConventions5.3StaticSemanticRules

6ECMAScriptDataTypesandValues6.1ECMAScriptLanguageTypes6.1.1TheUndeinedType6.1.2TheNullType6.1.3TheBooleanType6.1.4TheStringType6.1.5TheSymbolType6.1.5.1WellKnownSymbols

6.1.6TheNumberType6.1.7TheObjectType6.1.7.1PropertyAttributes6.1.7.2ObjectInternalMethodsandInternalSlots6.1.7.3InvariantsoftheEssentialInternalMethods6.1.7.4WellKnownIntrinsicObjects

6.2ECMAScriptSpeciicationTypes6.2.1TheListandRecordSpeciicationTypes6.2.2TheSetandRelationSpeciicationTypes6.2.3TheCompletionRecordSpeciicationType

6.2.3.1NormalCompletion6.2.3.2ImplicitCompletionValues6.2.3.3ThrowanException6.2.3.4ReturnIfAbrupt6.2.3.5UpdateEmpty(completionRecord,value)

6.2.4TheReferenceSpeciicationType6.2.4.1GetValue(V)6.2.4.2PutValue(V,W)6.2.4.3GetThisValue(V)6.2.4.4InitializeReferencedBinding(V,W)

6.2.5ThePropertyDescriptorSpeciicationType6.2.5.1IsAccessorDescriptor(Desc)6.2.5.2IsDataDescriptor(Desc)6.2.5.3IsGenericDescriptor(Desc)6.2.5.4FromPropertyDescriptor(Desc)6.2.5.5ToPropertyDescriptor(Obj)6.2.5.6CompletePropertyDescriptor(Desc)

6.2.6TheLexicalEnvironmentandEnvironmentRecordSpeciicationTypes6.2.7DataBlocks6.2.7.1CreateByteDataBlock(size)6.2.7.2CreateSharedByteDataBlock(size)6.2.7.3CopyDataBlockBytes(toBlock,toIndex,fromBlock,fromIndex,count)

7AbstractOperations7.1TypeConversion7.1.1ToPrimitive(input[,PreferredType])7.1.1.1OrdinaryToPrimitive(O,hint)

7.1.2ToBoolean(argument)7.1.3ToNumber(argument)7.1.3.1ToNumberAppliedtotheStringType7.1.3.1.1RS:MV

7.1.4ToInteger(argument)7.1.5ToInt32(argument)7.1.6ToUint32(argument)7.1.7ToInt16(argument)7.1.8ToUint16(argument)7.1.9ToInt8(argument)7.1.10ToUint8(argument)7.1.11ToUint8Clamp(argument)7.1.12ToString(argument)7.1.12.1ToStringAppliedtotheNumberType

7.1.13ToObject(argument)7.1.14ToPropertyKey(argument)7.1.15ToLength(argument)7.1.16CanonicalNumericIndexString(argument)7.1.17ToIndex(value)

7.2TestingandComparisonOperations7.2.1RequireObjectCoercible(argument)7.2.2IsArray(argument)7.2.3IsCallable(argument)7.2.4IsConstructor(argument)7.2.5IsExtensible(O)7.2.6IsInteger(argument)7.2.7IsPropertyKey(argument)7.2.8IsRegExp(argument)7.2.9SameValue(x,y)7.2.10SameValueZero(x,y)7.2.11SameValueNonNumber(x,y)7.2.12AbstractRelationalComparison7.2.13AbstractEqualityComparison7.2.14StrictEqualityComparison

7.3OperationsonObjects7.3.1Get(O,P)7.3.2GetV(V,P)7.3.3Set(O,P,V,Throw)7.3.4CreateDataProperty(O,P,V)7.3.5CreateMethodProperty(O,P,V)7.3.6CreateDataPropertyOrThrow(O,P,V)7.3.7DeinePropertyOrThrow(O,P,desc)7.3.8DeletePropertyOrThrow(O,P)7.3.9GetMethod(V,P)7.3.10HasProperty(O,P)7.3.11HasOwnProperty(O,P)7.3.12Call(F,V[,argumentsList])7.3.13Construct(F[,argumentsList[,newTarget]])7.3.14SetIntegrityLevel(O,level)7.3.15TestIntegrityLevel(O,level)7.3.16CreateArrayFromList(elements)7.3.17CreateListFromArrayLike(obj[,elementTypes])7.3.18Invoke(V,P[,argumentsList])7.3.19OrdinaryHasInstance(C,O)

7.3.20SpeciesConstructor(O,defaultConstructor)7.3.21EnumerableOwnProperties(O,kind)7.3.22GetFunctionRealm(obj)

7.4OperationsonIteratorObjects7.4.1GetIterator(obj[,method])7.4.2IteratorNext(iterator[,value])7.4.3IteratorComplete(iterResult)7.4.4IteratorValue(iterResult)7.4.5IteratorStep(iterator)7.4.6IteratorClose(iterator,completion)7.4.7CreateIterResultObject(value,done)7.4.8CreateListIterator(list)7.4.8.1ListIteratornext()

8ExecutableCodeandExecutionContexts8.1LexicalEnvironments8.1.1EnvironmentRecords8.1.1.1DeclarativeEnvironmentRecords8.1.1.1.1HasBinding(N)8.1.1.1.2CreateMutableBinding(N,D)8.1.1.1.3CreateImmutableBinding(N,S)8.1.1.1.4InitializeBinding(N,V)8.1.1.1.5SetMutableBinding(N,V,S)8.1.1.1.6GetBindingValue(N,S)8.1.1.1.7DeleteBinding(N)8.1.1.1.8HasThisBinding()8.1.1.1.9HasSuperBinding()8.1.1.1.10WithBaseObject()

8.1.1.2ObjectEnvironmentRecords8.1.1.2.1HasBinding(N)8.1.1.2.2CreateMutableBinding(N,D)8.1.1.2.3CreateImmutableBinding(N,S)8.1.1.2.4InitializeBinding(N,V)8.1.1.2.5SetMutableBinding(N,V,S)8.1.1.2.6GetBindingValue(N,S)8.1.1.2.7DeleteBinding(N)8.1.1.2.8HasThisBinding()8.1.1.2.9HasSuperBinding()8.1.1.2.10WithBaseObject()

8.1.1.3FunctionEnvironmentRecords8.1.1.3.1BindThisValue(V)

8.1.1.3.2HasThisBinding()8.1.1.3.3HasSuperBinding()8.1.1.3.4GetThisBinding()8.1.1.3.5GetSuperBase()

8.1.1.4GlobalEnvironmentRecords8.1.1.4.1HasBinding(N)8.1.1.4.2CreateMutableBinding(N,D)8.1.1.4.3CreateImmutableBinding(N,S)8.1.1.4.4InitializeBinding(N,V)8.1.1.4.5SetMutableBinding(N,V,S)8.1.1.4.6GetBindingValue(N,S)8.1.1.4.7DeleteBinding(N)8.1.1.4.8HasThisBinding()8.1.1.4.9HasSuperBinding()8.1.1.4.10WithBaseObject()8.1.1.4.11GetThisBinding()8.1.1.4.12HasVarDeclaration(N)8.1.1.4.13HasLexicalDeclaration(N)8.1.1.4.14HasRestrictedGlobalProperty(N)8.1.1.4.15CanDeclareGlobalVar(N)8.1.1.4.16CanDeclareGlobalFunction(N)8.1.1.4.17CreateGlobalVarBinding(N,D)8.1.1.4.18CreateGlobalFunctionBinding(N,V,D)

8.1.1.5ModuleEnvironmentRecords8.1.1.5.1GetBindingValue(N,S)8.1.1.5.2DeleteBinding(N)8.1.1.5.3HasThisBinding()8.1.1.5.4GetThisBinding()8.1.1.5.5CreateImportBinding(N,M,N2)

8.1.2LexicalEnvironmentOperations8.1.2.1GetIdentiierReference(lex,name,strict)8.1.2.2NewDeclarativeEnvironment(E)8.1.2.3NewObjectEnvironment(O,E)8.1.2.4NewFunctionEnvironment(F,newTarget)8.1.2.5NewGlobalEnvironment(G,thisValue)8.1.2.6NewModuleEnvironment(E)

8.2Realms8.2.1CreateRealm()8.2.2CreateIntrinsics(realmRec)8.2.3SetRealmGlobalObject(realmRec,globalObj,thisValue)

8.2.4SetDefaultGlobalBindings(realmRec)8.3ExecutionContexts8.3.1GetActiveScriptOrModule()8.3.2ResolveBinding(name[,env])8.3.3GetThisEnvironment()8.3.4ResolveThisBinding()8.3.5GetNewTarget()8.3.6GetGlobalObject()

8.4JobsandJobQueues8.4.1EnqueueJob(queueName,job,arguments)

8.5InitializeHostDeinedRealm()8.6RunJobs()8.7Agents8.7.1AgentSigniier()8.7.2AgentCanSuspend()

8.8AgentClusters8.9ForwardProgress

9OrdinaryandExoticObjectsBehaviours9.1OrdinaryObjectInternalMethodsandInternalSlots9.1.1[[GetPrototypeOf]]()9.1.1.1OrdinaryGetPrototypeOf(O)

9.1.2[[SetPrototypeOf]](V)9.1.2.1OrdinarySetPrototypeOf(O,V)

9.1.3[[IsExtensible]]()9.1.3.1OrdinaryIsExtensible(O)

9.1.4[[PreventExtensions]]()9.1.4.1OrdinaryPreventExtensions(O)

9.1.5[[GetOwnProperty]](P)9.1.5.1OrdinaryGetOwnProperty(O,P)

9.1.6[[DeineOwnProperty]](P,Desc)9.1.6.1OrdinaryDeineOwnProperty(O,P,Desc)9.1.6.2IsCompatiblePropertyDescriptor(Extensible,Desc,Current)9.1.6.3ValidateAndApplyPropertyDescriptor(O,P,extensible,Desc,current)

9.1.7[[HasProperty]](P)9.1.7.1OrdinaryHasProperty(O,P)

9.1.8[[Get]](P,Receiver)9.1.8.1OrdinaryGet(O,P,Receiver)

9.1.9[[Set]](P,V,Receiver)9.1.9.1OrdinarySet(O,P,V,Receiver)

9.1.10[[Delete]](P)

9.1.10.1OrdinaryDelete(O,P)9.1.11[[OwnPropertyKeys]]()9.1.11.1OrdinaryOwnPropertyKeys(O)

9.1.12ObjectCreate(proto[,internalSlotsList])9.1.13OrdinaryCreateFromConstructor(constructor,intrinsicDefaultProto[,internalSlotsList])9.1.14GetPrototypeFromConstructor(constructor,intrinsicDefaultProto)

9.2ECMAScriptFunctionObjects9.2.1[[Call]](thisArgument,argumentsList)9.2.1.1PrepareForOrdinaryCall(F,newTarget)9.2.1.2OrdinaryCallBindThis(F,calleeContext,thisArgument)9.2.1.3OrdinaryCallEvaluateBody(F,argumentsList)

9.2.2[[Construct]](argumentsList,newTarget)9.2.3FunctionAllocate(functionPrototype,strict,functionKind)9.2.4FunctionInitialize(F,kind,ParameterList,Body,Scope)9.2.5FunctionCreate(kind,ParameterList,Body,Scope,Strict[,prototype])9.2.6GeneratorFunctionCreate(kind,ParameterList,Body,Scope,Strict)9.2.7AddRestrictedFunctionProperties(F,realm)9.2.7.1%ThrowTypeError%()

9.2.8MakeConstructor(F[,writablePrototype[,prototype]])9.2.9MakeClassConstructor(F)9.2.10MakeMethod(F,homeObject)9.2.11SetFunctionName(F,name[,preix])9.2.12FunctionDeclarationInstantiation(func,argumentsList)

9.3BuiltinFunctionObjects9.3.1[[Call]](thisArgument,argumentsList)9.3.2[[Construct]](argumentsList,newTarget)9.3.3CreateBuiltinFunction(realm,steps,prototype[,internalSlotsList])

9.4BuiltinExoticObjectInternalMethodsandSlots9.4.1BoundFunctionExoticObjects9.4.1.1[[Call]](thisArgument,argumentsList)9.4.1.2[[Construct]](argumentsList,newTarget)9.4.1.3BoundFunctionCreate(targetFunction,boundThis,boundArgs)

9.4.2ArrayExoticObjects9.4.2.1[[DeineOwnProperty]](P,Desc)9.4.2.2ArrayCreate(length[,proto])9.4.2.3ArraySpeciesCreate(originalArray,length)9.4.2.4ArraySetLength(A,Desc)

9.4.3StringExoticObjects9.4.3.1[[GetOwnProperty]](P)9.4.3.2[[DeineOwnProperty]](P,Desc)

9.4.3.3[[OwnPropertyKeys]]()9.4.3.4StringCreate(value,prototype)9.4.3.5StringGetOwnProperty(S,P)

9.4.4ArgumentsExoticObjects9.4.4.1[[GetOwnProperty]](P)9.4.4.2[[DeineOwnProperty]](P,Desc)9.4.4.3[[Get]](P,Receiver)9.4.4.4[[Set]](P,V,Receiver)9.4.4.5[[Delete]](P)9.4.4.6CreateUnmappedArgumentsObject(argumentsList)9.4.4.7CreateMappedArgumentsObject(func,formals,argumentsList,env)9.4.4.7.1MakeArgGetter(name,env)9.4.4.7.2MakeArgSetter(name,env)

9.4.5IntegerIndexedExoticObjects9.4.5.1[[GetOwnProperty]](P)9.4.5.2[[HasProperty]](P)9.4.5.3[[DeineOwnProperty]](P,Desc)9.4.5.4[[Get]](P,Receiver)9.4.5.5[[Set]](P,V,Receiver)9.4.5.6[[OwnPropertyKeys]]()9.4.5.7IntegerIndexedObjectCreate(prototype,internalSlotsList)9.4.5.8IntegerIndexedElementGet(O,index)9.4.5.9IntegerIndexedElementSet(O,index,value)

9.4.6ModuleNamespaceExoticObjects9.4.6.1[[SetPrototypeOf]](V)9.4.6.2[[IsExtensible]]()9.4.6.3[[PreventExtensions]]()9.4.6.4[[GetOwnProperty]](P)9.4.6.5[[DeineOwnProperty]](P,Desc)9.4.6.6[[HasProperty]](P)9.4.6.7[[Get]](P,Receiver)9.4.6.8[[Set]](P,V,Receiver)9.4.6.9[[Delete]](P)9.4.6.10[[OwnPropertyKeys]]()9.4.6.11ModuleNamespaceCreate(module,exports)

9.4.7ImmutablePrototypeExoticObjects9.4.7.1[[SetPrototypeOf]](V)9.4.7.2SetImmutablePrototype(O,V)

9.5ProxyObjectInternalMethodsandInternalSlots9.5.1[[GetPrototypeOf]]()

9.5.2[[SetPrototypeOf]](V)9.5.3[[IsExtensible]]()9.5.4[[PreventExtensions]]()9.5.5[[GetOwnProperty]](P)9.5.6[[DeineOwnProperty]](P,Desc)9.5.7[[HasProperty]](P)9.5.8[[Get]](P,Receiver)9.5.9[[Set]](P,V,Receiver)9.5.10[[Delete]](P)9.5.11[[OwnPropertyKeys]]()9.5.12[[Call]](thisArgument,argumentsList)9.5.13[[Construct]](argumentsList,newTarget)9.5.14ProxyCreate(target,handler)

10ECMAScriptLanguage:SourceCode10.1SourceText10.1.1SS:UTF16Encoding(cp)10.1.2SS:UTF16Decode(lead,trail)

10.2TypesofSourceCode10.2.1StrictModeCode10.2.2NonECMAScriptFunctions

11ECMAScriptLanguage:LexicalGrammar11.1UnicodeFormatControlCharacters11.2WhiteSpace11.3LineTerminators11.4Comments11.5Tokens11.6NamesandKeywords11.6.1IdentiierNames11.6.1.1SS:EarlyErrors11.6.1.2SS:StringValue

11.6.2ReservedWords11.6.2.1Keywords11.6.2.2FutureReservedWords

11.7Punctuators11.8Literals11.8.1NullLiterals11.8.2BooleanLiterals11.8.3NumericLiterals11.8.3.1SS:MV

11.8.4StringLiterals

11.8.4.1SS:EarlyErrors11.8.4.2SS:StringValue11.8.4.3SS:SV

11.8.5RegularExpressionLiterals11.8.5.1SS:EarlyErrors11.8.5.2SS:BodyText11.8.5.3SS:FlagText

11.8.6TemplateLiteralLexicalComponents11.8.6.1SS:TVandTRV

11.9AutomaticSemicolonInsertion11.9.1RulesofAutomaticSemicolonInsertion11.9.2ExamplesofAutomaticSemicolonInsertion

12ECMAScriptLanguage:Expressions12.1Identiiers12.1.1SS:EarlyErrors12.1.2SS:BoundNames12.1.3SS:IsValidSimpleAssignmentTarget12.1.4SS:StringValue12.1.5RS:BindingInitialization12.1.5.1RS:InitializeBoundName(name,value,environment)

12.1.6RS:Evaluation12.2PrimaryExpression12.2.1Semantics12.2.1.1SS:CoveredParenthesizedExpression12.2.1.2SS:HasName12.2.1.3SS:IsFunctionDeinition12.2.1.4SS:IsIdentiierRef12.2.1.5SS:IsValidSimpleAssignmentTarget

12.2.2ThethisKeyword12.2.2.1RS:Evaluation

12.2.3IdentiierReference12.2.4Literals12.2.4.1RS:Evaluation

12.2.5ArrayInitializer12.2.5.1SS:ElisionWidth12.2.5.2RS:ArrayAccumulation12.2.5.3RS:Evaluation

12.2.6ObjectInitializer12.2.6.1SS:EarlyErrors12.2.6.2SS:ComputedPropertyContains

12.2.6.3SS:Contains12.2.6.4SS:IsComputedPropertyKey12.2.6.5SS:PropName12.2.6.6SS:PropertyNameList12.2.6.7RS:Evaluation12.2.6.8RS:PropertyDeinitionEvaluation

12.2.7FunctionDeiningExpressions12.2.8RegularExpressionLiterals12.2.8.1SS:EarlyErrors12.2.8.2RS:Evaluation

12.2.9TemplateLiterals12.2.9.1SS:TemplateStrings12.2.9.2RS:ArgumentListEvaluation12.2.9.3RS:GetTemplateObject(templateLiteral)12.2.9.4RS:SubstitutionEvaluation12.2.9.5RS:Evaluation

12.2.10TheGroupingOperator12.2.10.1SS:EarlyErrors12.2.10.2SS:IsFunctionDeinition12.2.10.3SS:IsValidSimpleAssignmentTarget12.2.10.4RS:Evaluation

12.3LeftHandSideExpressions12.3.1StaticSemantics12.3.1.1SS:CoveredCallExpression12.3.1.2SS:Contains12.3.1.3SS:IsFunctionDeinition12.3.1.4SS:IsDestructuring12.3.1.5SS:IsIdentiierRef12.3.1.6SS:IsValidSimpleAssignmentTarget

12.3.2PropertyAccessors12.3.2.1RS:Evaluation

12.3.3ThenewOperator12.3.3.1RS:Evaluation12.3.3.1.1RS:EvaluateNew(constructExpr,arguments)

12.3.4FunctionCalls12.3.4.1RS:Evaluation12.3.4.2RS:EvaluateCall(ref,arguments,tailPosition)12.3.4.3RS:EvaluateDirectCall(func,thisValue,arguments,tailPosition)

12.3.5ThesuperKeyword12.3.5.1RS:Evaluation

12.3.5.2RS:GetSuperConstructor()12.3.5.3RS:MakeSuperPropertyReference(propertyKey,strict)

12.3.6ArgumentLists12.3.6.1RS:ArgumentListEvaluation

12.3.7TaggedTemplates12.3.7.1RS:Evaluation

12.3.8MetaProperties12.3.8.1RS:Evaluation

12.4UpdateExpressions12.4.1SS:EarlyErrors12.4.2SS:IsFunctionDeinition12.4.3SS:IsValidSimpleAssignmentTarget12.4.4PostixIncrementOperator12.4.4.1RS:Evaluation

12.4.5PostixDecrementOperator12.4.5.1RS:Evaluation

12.4.6PreixIncrementOperator12.4.6.1RS:Evaluation

12.4.7PreixDecrementOperator12.4.7.1RS:Evaluation

12.5UnaryOperators12.5.1SS:IsFunctionDeinition12.5.2SS:IsValidSimpleAssignmentTarget12.5.3ThedeleteOperator12.5.3.1SS:EarlyErrors12.5.3.2RS:Evaluation

12.5.4ThevoidOperator12.5.4.1RS:Evaluation

12.5.5ThetypeofOperator12.5.5.1RS:Evaluation

12.5.6Unary+Operator12.5.6.1RS:Evaluation

12.5.7UnaryOperator12.5.7.1RS:Evaluation

12.5.8BitwiseNOTOperator(~)12.5.8.1RS:Evaluation

12.5.9LogicalNOTOperator(!)12.5.9.1RS:Evaluation

12.6ExponentiationOperator12.6.1SS:IsFunctionDeinition

12.6.2SS:IsValidSimpleAssignmentTarget12.6.3RS:Evaluation12.6.4Applyingthe**Operator

12.7MultiplicativeOperators12.7.1SS:IsFunctionDeinition12.7.2SS:IsValidSimpleAssignmentTarget12.7.3RS:Evaluation12.7.3.1Applyingthe*Operator12.7.3.2Applyingthe/Operator12.7.3.3Applyingthe%Operator

12.8AdditiveOperators12.8.1SS:IsFunctionDeinition12.8.2SS:IsValidSimpleAssignmentTarget12.8.3TheAdditionOperator(+)12.8.3.1RS:Evaluation

12.8.4TheSubtractionOperator()12.8.4.1RS:Evaluation

12.8.5ApplyingtheAdditiveOperatorstoNumbers12.9BitwiseShiftOperators12.9.1SS:IsFunctionDeinition12.9.2SS:IsValidSimpleAssignmentTarget12.9.3TheLeftShiftOperator()12.9.4.1RS:Evaluation

12.9.5TheUnsignedRightShiftOperator(>>>)12.9.5.1RS:Evaluation

12.10RelationalOperators12.10.1SS:IsFunctionDeinition12.10.2SS:IsValidSimpleAssignmentTarget12.10.3RS:Evaluation12.10.4RS:InstanceofOperator(O,C)

12.11EqualityOperators12.11.1SS:IsFunctionDeinition12.11.2SS:IsValidSimpleAssignmentTarget12.11.3RS:Evaluation

12.12BinaryBitwiseOperators12.12.1SS:IsFunctionDeinition12.12.2SS:IsValidSimpleAssignmentTarget12.12.3RS:Evaluation

12.13BinaryLogicalOperators12.13.1SS:IsFunctionDeinition12.13.2SS:IsValidSimpleAssignmentTarget12.13.3RS:Evaluation

12.14ConditionalOperator(?:)12.14.1SS:IsFunctionDeinition12.14.2SS:IsValidSimpleAssignmentTarget12.14.3RS:Evaluation

12.15AssignmentOperators12.15.1SS:EarlyErrors12.15.2SS:IsFunctionDeinition12.15.3SS:IsValidSimpleAssignmentTarget12.15.4RS:Evaluation12.15.5DestructuringAssignment12.15.5.1SS:EarlyErrors12.15.5.2RS:DestructuringAssignmentEvaluation12.15.5.3RS:IteratorDestructuringAssignmentEvaluation12.15.5.4RS:KeyedDestructuringAssignmentEvaluation

12.16CommaOperator(,)12.16.1SS:IsFunctionDeinition12.16.2SS:IsValidSimpleAssignmentTarget12.16.3RS:Evaluation

13ECMAScriptLanguage:StatementsandDeclarations13.1StatementSemantics13.1.1SS:ContainsDuplicateLabels13.1.2SS:ContainsUndeinedBreakTarget13.1.3SS:ContainsUndeinedContinueTarget13.1.4SS:DeclarationPart13.1.5SS:VarDeclaredNames13.1.6SS:VarScopedDeclarations13.1.7RS:LabelledEvaluation13.1.8RS:Evaluation

13.2Block13.2.1SS:EarlyErrors13.2.2SS:ContainsDuplicateLabels13.2.3SS:ContainsUndeinedBreakTarget13.2.4SS:ContainsUndeinedContinueTarget13.2.5SS:LexicallyDeclaredNames13.2.6SS:LexicallyScopedDeclarations13.2.7SS:TopLevelLexicallyDeclaredNames

13.2.8SS:TopLevelLexicallyScopedDeclarations13.2.9SS:TopLevelVarDeclaredNames13.2.10SS:TopLevelVarScopedDeclarations13.2.11SS:VarDeclaredNames13.2.12SS:VarScopedDeclarations13.2.13RS:Evaluation13.2.14RS:BlockDeclarationInstantiation(code,env)

13.3DeclarationsandtheVariableStatement13.3.1LetandConstDeclarations13.3.1.1SS:EarlyErrors13.3.1.2SS:BoundNames13.3.1.3SS:IsConstantDeclaration13.3.1.4RS:Evaluation

13.3.2VariableStatement13.3.2.1SS:BoundNames13.3.2.2SS:VarDeclaredNames13.3.2.3SS:VarScopedDeclarations13.3.2.4RS:Evaluation

13.3.3DestructuringBindingPatterns13.3.3.1SS:BoundNames13.3.3.2SS:ContainsExpression13.3.3.3SS:HasInitializer13.3.3.4SS:IsSimpleParameterList13.3.3.5RS:BindingInitialization13.3.3.6RS:IteratorBindingInitialization13.3.3.7RS:KeyedBindingInitialization

13.4EmptyStatement13.4.1RS:Evaluation

13.5ExpressionStatement13.5.1RS:Evaluation

13.6TheifStatement13.6.1SS:EarlyErrors13.6.2SS:ContainsDuplicateLabels13.6.3SS:ContainsUndeinedBreakTarget13.6.4SS:ContainsUndeinedContinueTarget13.6.5SS:VarDeclaredNames13.6.6SS:VarScopedDeclarations13.6.7RS:Evaluation

13.7IterationStatements13.7.1Semantics

13.7.1.1SS:EarlyErrors13.7.1.2RS:LoopContinues(completion,labelSet)

13.7.2ThedowhileStatement13.7.2.1SS:ContainsDuplicateLabels13.7.2.2SS:ContainsUndeinedBreakTarget13.7.2.3SS:ContainsUndeinedContinueTarget13.7.2.4SS:VarDeclaredNames13.7.2.5SS:VarScopedDeclarations13.7.2.6RS:LabelledEvaluation

13.7.3ThewhileStatement13.7.3.1SS:ContainsDuplicateLabels13.7.3.2SS:ContainsUndeinedBreakTarget13.7.3.3SS:ContainsUndeinedContinueTarget13.7.3.4SS:VarDeclaredNames13.7.3.5SS:VarScopedDeclarations13.7.3.6RS:LabelledEvaluation

13.7.4TheforStatement13.7.4.1SS:EarlyErrors13.7.4.2SS:ContainsDuplicateLabels13.7.4.3SS:ContainsUndeinedBreakTarget13.7.4.4SS:ContainsUndeinedContinueTarget13.7.4.5SS:VarDeclaredNames13.7.4.6SS:VarScopedDeclarations13.7.4.7RS:LabelledEvaluation13.7.4.8RS:ForBodyEvaluation(test,increment,stmt,perIterationBindings,labelSet)13.7.4.9RS:CreatePerIterationEnvironment(perIterationBindings)

13.7.5TheforinandforofStatements13.7.5.1SS:EarlyErrors13.7.5.2SS:BoundNames13.7.5.3SS:ContainsDuplicateLabels13.7.5.4SS:ContainsUndeinedBreakTarget13.7.5.5SS:ContainsUndeinedContinueTarget13.7.5.6SS:IsDestructuring13.7.5.7SS:VarDeclaredNames13.7.5.8SS:VarScopedDeclarations13.7.5.9RS:BindingInitialization13.7.5.10RS:BindingInstantiation13.7.5.11RS:LabelledEvaluation13.7.5.12RS:ForIn/OfHeadEvaluation(TDZnames,expr,iterationKind)13.7.5.13RS:ForIn/OfBodyEvaluation(lhs,stmt,iterator,iterationKind,lhsKind,labelSet)

13.7.5.14RS:Evaluation13.7.5.15EnumerateObjectProperties(O)

13.8ThecontinueStatement13.8.1SS:EarlyErrors13.8.2SS:ContainsUndeinedContinueTarget13.8.3RS:Evaluation

13.9ThebreakStatement13.9.1SS:EarlyErrors13.9.2SS:ContainsUndeinedBreakTarget13.9.3RS:Evaluation

13.10ThereturnStatement13.10.1RS:Evaluation

13.11ThewithStatement13.11.1SS:EarlyErrors13.11.2SS:ContainsDuplicateLabels13.11.3SS:ContainsUndeinedBreakTarget13.11.4SS:ContainsUndeinedContinueTarget13.11.5SS:VarDeclaredNames13.11.6SS:VarScopedDeclarations13.11.7RS:Evaluation

13.12TheswitchStatement13.12.1SS:EarlyErrors13.12.2SS:ContainsDuplicateLabels13.12.3SS:ContainsUndeinedBreakTarget13.12.4SS:ContainsUndeinedContinueTarget13.12.5SS:LexicallyDeclaredNames13.12.6SS:LexicallyScopedDeclarations13.12.7SS:VarDeclaredNames13.12.8SS:VarScopedDeclarations13.12.9RS:CaseBlockEvaluation13.12.10RS:CaseSelectorEvaluation13.12.11RS:Evaluation

13.13LabelledStatements13.13.1SS:EarlyErrors13.13.2SS:ContainsDuplicateLabels13.13.3SS:ContainsUndeinedBreakTarget13.13.4SS:ContainsUndeinedContinueTarget13.13.5SS:IsLabelledFunction(stmt)13.13.6SS:LexicallyDeclaredNames13.13.7SS:LexicallyScopedDeclarations

13.13.8SS:TopLevelLexicallyDeclaredNames13.13.9SS:TopLevelLexicallyScopedDeclarations13.13.10SS:TopLevelVarDeclaredNames13.13.11SS:TopLevelVarScopedDeclarations13.13.12SS:VarDeclaredNames13.13.13SS:VarScopedDeclarations13.13.14RS:LabelledEvaluation13.13.15RS:Evaluation

13.14ThethrowStatement13.14.1RS:Evaluation

13.15ThetryStatement13.15.1SS:EarlyErrors13.15.2SS:ContainsDuplicateLabels13.15.3SS:ContainsUndeinedBreakTarget13.15.4SS:ContainsUndeinedContinueTarget13.15.5SS:VarDeclaredNames13.15.6SS:VarScopedDeclarations13.15.7RS:CatchClauseEvaluation13.15.8RS:Evaluation

13.16ThedebuggerStatement13.16.1RS:Evaluation

14ECMAScriptLanguage:FunctionsandClasses14.1FunctionDeinitions14.1.1DirectiveProloguesandtheUseStrictDirective14.1.2SS:EarlyErrors14.1.3SS:BoundNames14.1.4SS:Contains14.1.5SS:ContainsExpression14.1.6SS:ContainsUseStrict14.1.7SS:ExpectedArgumentCount14.1.8SS:HasInitializer14.1.9SS:HasName14.1.10SS:IsAnonymousFunctionDeinition(expr)14.1.11SS:IsConstantDeclaration14.1.12SS:IsFunctionDeinition14.1.13SS:IsSimpleParameterList14.1.14SS:LexicallyDeclaredNames14.1.15SS:LexicallyScopedDeclarations14.1.16SS:VarDeclaredNames14.1.17SS:VarScopedDeclarations

14.1.18RS:EvaluateBody14.1.19RS:IteratorBindingInitialization14.1.20RS:InstantiateFunctionObject14.1.21RS:Evaluation

14.2ArrowFunctionDeinitions14.2.1SS:EarlyErrors14.2.2SS:BoundNames14.2.3SS:Contains14.2.4SS:ContainsExpression14.2.5SS:ContainsUseStrict14.2.6SS:ExpectedArgumentCount14.2.7SS:HasName14.2.8SS:IsSimpleParameterList14.2.9SS:CoveredFormalsList14.2.10SS:LexicallyDeclaredNames14.2.11SS:LexicallyScopedDeclarations14.2.12SS:VarDeclaredNames14.2.13SS:VarScopedDeclarations14.2.14RS:IteratorBindingInitialization14.2.15RS:EvaluateBody14.2.16RS:Evaluation

14.3MethodDeinitions14.3.1SS:EarlyErrors14.3.2SS:ComputedPropertyContains14.3.3SS:ExpectedArgumentCount14.3.4SS:HasDirectSuper14.3.5SS:PropName14.3.6SS:SpecialMethod14.3.7RS:DeineMethod14.3.8RS:PropertyDeinitionEvaluation

14.4GeneratorFunctionDeinitions14.4.1SS:EarlyErrors14.4.2SS:BoundNames14.4.3SS:ComputedPropertyContains14.4.4SS:Contains14.4.5SS:HasDirectSuper14.4.6SS:HasName14.4.7SS:IsConstantDeclaration14.4.8SS:IsFunctionDeinition14.4.9SS:PropName

14.4.10RS:EvaluateBody14.4.11RS:InstantiateFunctionObject14.4.12RS:PropertyDeinitionEvaluation14.4.13RS:Evaluation

14.5ClassDeinitions14.5.1SS:EarlyErrors14.5.2SS:BoundNames14.5.3SS:ConstructorMethod14.5.4SS:Contains14.5.5SS:ComputedPropertyContains14.5.6SS:HasName14.5.7SS:IsConstantDeclaration14.5.8SS:IsFunctionDeinition14.5.9SS:IsStatic14.5.10SS:NonConstructorMethodDeinitions14.5.11SS:PrototypePropertyNameList14.5.12SS:PropName14.5.13RS:ClassDeinitionEvaluation14.5.14RS:BindingClassDeclarationEvaluation14.5.15RS:Evaluation

14.6AsyncFunctionDeinitions14.6.1SS:EarlyErrors14.6.2SS:BoundNames14.6.3SS:ComputedPropertyContains14.6.4SS:Contains14.6.5SS:HasDirectSuper14.6.6SS:HasName14.6.7SS:IsConstantDeclaration14.6.8SS:IsFunctionDeinition14.6.9SS:PropName14.6.10RS:InstantiateFunctionObject14.6.11RS:EvaluateBody14.6.12RS:PropertyDeinitionEvaluation14.6.13RS:Evaluation

14.7AsyncArrowFunctionDeinitions14.7.1SS:EarlyErrors14.7.2SS:CoveredAsyncArrowHead14.7.3SS:BoundNames14.7.4SS:Contains14.7.5SS:ContainsExpression

14.7.6SS:ExpectedArgumentCount14.7.7SS:HasName14.7.8SS:IsSimpleParameterList14.7.9SS:LexicallyDeclaredNames14.7.10SS:LexicallyScopedDeclarations14.7.11SS:VarDeclaredNames14.7.12SS:VarScopedDeclarations14.7.13RS:IteratorBindingInitialization14.7.14RS:EvaluateBody14.7.15RS:Evaluation

14.8TailPositionCalls14.8.1SS:IsInTailPosition(call)14.8.2SS:HasCallInTailPosition14.8.2.1StatementRules14.8.2.2ExpressionRules

14.8.3RS:PrepareForTailCall()15ECMAScriptLanguage:ScriptsandModules15.1Scripts15.1.1SS:EarlyErrors15.1.2SS:IsStrict15.1.3SS:LexicallyDeclaredNames15.1.4SS:LexicallyScopedDeclarations15.1.5SS:VarDeclaredNames15.1.6SS:VarScopedDeclarations15.1.7RS:Evaluation15.1.8ScriptRecords15.1.9ParseScript(sourceText,realm,hostDeined)15.1.10ScriptEvaluation(scriptRecord)15.1.11RS:GlobalDeclarationInstantiation(script,env)15.1.12RS:ScriptEvaluationJob(sourceText,hostDeined)

15.2Modules15.2.1ModuleSemantics15.2.1.1SS:EarlyErrors15.2.1.2SS:ContainsDuplicateLabels15.2.1.3SS:ContainsUndeinedBreakTarget15.2.1.4SS:ContainsUndeinedContinueTarget15.2.1.5SS:ExportedBindings15.2.1.6SS:ExportedNames15.2.1.7SS:ExportEntries15.2.1.8SS:ImportEntries

15.2.1.9SS:ImportedLocalNames(importEntries)15.2.1.10SS:ModuleRequests15.2.1.11SS:LexicallyDeclaredNames15.2.1.12SS:LexicallyScopedDeclarations15.2.1.13SS:VarDeclaredNames15.2.1.14SS:VarScopedDeclarations15.2.1.15AbstractModuleRecords15.2.1.16SourceTextModuleRecords15.2.1.16.1ParseModule(sourceText,realm,hostDeined)15.2.1.16.2GetExportedNames(exportStarSet)ConcreteMethod15.2.1.16.3ResolveExport(exportName,resolveSet)ConcreteMethod15.2.1.16.4ModuleDeclarationInstantiation()ConcreteMethod15.2.1.16.5ModuleEvaluation()ConcreteMethod

15.2.1.17RS:HostResolveImportedModule(referencingModule,speciier)15.2.1.18RS:GetModuleNamespace(module)15.2.1.19RS:TopLevelModuleEvaluationJob(sourceText,hostDeined)15.2.1.20RS:Evaluation

15.2.2Imports15.2.2.1SS:EarlyErrors15.2.2.2SS:BoundNames15.2.2.3SS:ImportEntries15.2.2.4SS:ImportEntriesForModule15.2.2.5SS:ModuleRequests

15.2.3Exports15.2.3.1SS:EarlyErrors15.2.3.2SS:BoundNames15.2.3.3SS:ExportedBindings15.2.3.4SS:ExportedNames15.2.3.5SS:ExportEntries15.2.3.6SS:ExportEntriesForModule15.2.3.7SS:IsConstantDeclaration15.2.3.8SS:LexicallyScopedDeclarations15.2.3.9SS:ModuleRequests15.2.3.10SS:ReferencedBindings15.2.3.11RS:Evaluation

16ErrorHandlingandLanguageExtensions16.1HostReportErrors(errorList)16.2ForbiddenExtensions

17ECMAScriptStandardBuiltinObjects18TheGlobalObject

18.1ValuePropertiesoftheGlobalObject18.1.1Ininity18.1.2NaN18.1.3undeined

18.2FunctionPropertiesoftheGlobalObject18.2.1eval(x)18.2.1.1RS:PerformEval(x,evalRealm,strictCaller,direct)18.2.1.1.1AdditionalEarlyErrorRulesforEvalOutsideFunctions18.2.1.1.2AdditionalEarlyErrorRulesforEvalOutsideMethods18.2.1.1.3AdditionalEarlyErrorRulesforEvalOutsideConstructorMethods

18.2.1.2HostEnsureCanCompileStrings(callerRealm,calleeRealm)18.2.1.3RS:EvalDeclarationInstantiation(body,varEnv,lexEnv,strict)

18.2.2isFinite(number)18.2.3isNaN(number)18.2.4parseFloat(string)18.2.5parseInt(string,radix)18.2.6URIHandlingFunctions18.2.6.1URISyntaxandSemantics18.2.6.1.1RS:Encode(string,unescapedSet)18.2.6.1.2RS:Decode(string,reservedSet)

18.2.6.2decodeURI(encodedURI)18.2.6.3decodeURIComponent(encodedURIComponent)18.2.6.4encodeURI(uri)18.2.6.5encodeURIComponent(uriComponent)

18.3ConstructorPropertiesoftheGlobalObject18.3.1Array(...)18.3.2ArrayBuffer(...)18.3.3Boolean(...)18.3.4DataView(...)18.3.5Date(...)18.3.6Error(...)18.3.7EvalError(...)18.3.8Float32Array(...)18.3.9Float64Array(...)18.3.10Function(...)18.3.11Int8Array(...)18.3.12Int16Array(...)18.3.13Int32Array(...)18.3.14Map(...)18.3.15Number(...)

18.3.16Object(...)18.3.17Proxy(...)18.3.18Promise(...)18.3.19RangeError(...)18.3.20ReferenceError(...)18.3.21RegExp(...)18.3.22Set(...)18.3.23SharedArrayBuffer(...)18.3.24String(...)18.3.25Symbol(...)18.3.26SyntaxError(...)18.3.27TypeError(...)18.3.28Uint8Array(...)18.3.29Uint8ClampedArray(...)18.3.30Uint16Array(...)18.3.31Uint32Array(...)18.3.32URIError(...)18.3.33WeakMap(...)18.3.34WeakSet(...)

18.4OtherPropertiesoftheGlobalObject18.4.1Atomics18.4.2JSON18.4.3Math18.4.4Relect

19FundamentalObjects19.1ObjectObjects19.1.1TheObjectConstructor19.1.1.1Object([value])

19.1.2PropertiesoftheObjectConstructor19.1.2.1Object.assign(target,...sources)19.1.2.2Object.create(O,Properties)19.1.2.3Object.deineProperties(O,Properties)19.1.2.3.1RS:ObjectDeineProperties(O,Properties)

19.1.2.4Object.deineProperty(O,P,Attributes)19.1.2.5Object.entries(O)19.1.2.6Object.freeze(O)19.1.2.7Object.getOwnPropertyDescriptor(O,P)19.1.2.8Object.getOwnPropertyDescriptors(O)19.1.2.9Object.getOwnPropertyNames(O)19.1.2.10Object.getOwnPropertySymbols(O)

19.1.2.10.1RS:GetOwnPropertyKeys(O,Type)19.1.2.11Object.getPrototypeOf(O)19.1.2.12Object.is(value1,value2)19.1.2.13Object.isExtensible(O)19.1.2.14Object.isFrozen(O)19.1.2.15Object.isSealed(O)19.1.2.16Object.keys(O)19.1.2.17Object.preventExtensions(O)19.1.2.18Object.prototype19.1.2.19Object.seal(O)19.1.2.20Object.setPrototypeOf(O,proto)19.1.2.21Object.values(O)

19.1.3PropertiesoftheObjectPrototypeObject19.1.3.1Object.prototype.constructor19.1.3.2Object.prototype.hasOwnProperty(V)19.1.3.3Object.prototype.isPrototypeOf(V)19.1.3.4Object.prototype.propertyIsEnumerable(V)19.1.3.5Object.prototype.toLocaleString([reserved1[,reserved2]])19.1.3.6Object.prototype.toString()19.1.3.7Object.prototype.valueOf()

19.1.4PropertiesofObjectInstances19.2FunctionObjects19.2.1TheFunctionConstructor19.2.1.1Function(p1,p2,,pn,body)19.2.1.1.1RS:CreateDynamicFunction(constructor,newTarget,kind,args)

19.2.2PropertiesoftheFunctionConstructor19.2.2.1Function.length19.2.2.2Function.prototype

19.2.3PropertiesoftheFunctionPrototypeObject19.2.3.1Function.prototype.apply(thisArg,argArray)19.2.3.2Function.prototype.bind(thisArg,...args)19.2.3.3Function.prototype.call(thisArg,...args)19.2.3.4Function.prototype.constructor19.2.3.5Function.prototype.toString()19.2.3.6Function.prototype[@@hasInstance](V)

19.2.4FunctionInstances19.2.4.1length19.2.4.2name19.2.4.3prototype

19.3BooleanObjects

19.3.1TheBooleanConstructor19.3.1.1Boolean(value)

19.3.2PropertiesoftheBooleanConstructor19.3.2.1Boolean.prototype

19.3.3PropertiesoftheBooleanPrototypeObject19.3.3.1Boolean.prototype.constructor19.3.3.2Boolean.prototype.toString()19.3.3.3Boolean.prototype.valueOf()

19.3.4PropertiesofBooleanInstances19.4SymbolObjects19.4.1TheSymbolConstructor19.4.1.1Symbol([description])

19.4.2PropertiesoftheSymbolConstructor19.4.2.1Symbol.for(key)19.4.2.2Symbol.hasInstance19.4.2.3Symbol.isConcatSpreadable19.4.2.4Symbol.iterator19.4.2.5Symbol.keyFor(sym)19.4.2.6Symbol.match19.4.2.7Symbol.prototype19.4.2.8Symbol.replace19.4.2.9Symbol.search19.4.2.10Symbol.species19.4.2.11Symbol.split19.4.2.12Symbol.toPrimitive19.4.2.13Symbol.toStringTag19.4.2.14Symbol.unscopables

19.4.3PropertiesoftheSymbolPrototypeObject19.4.3.1Symbol.prototype.constructor19.4.3.2Symbol.prototype.toString()19.4.3.2.1RS:SymbolDescriptiveString(sym)

19.4.3.3Symbol.prototype.valueOf()19.4.3.4Symbol.prototype[@@toPrimitive](hint)19.4.3.5Symbol.prototype[@@toStringTag]

19.4.4PropertiesofSymbolInstances19.5ErrorObjects19.5.1TheErrorConstructor19.5.1.1Error(message)

19.5.2PropertiesoftheErrorConstructor19.5.2.1Error.prototype

19.5.3PropertiesoftheErrorPrototypeObject19.5.3.1Error.prototype.constructor19.5.3.2Error.prototype.message19.5.3.3Error.prototype.name19.5.3.4Error.prototype.toString()

19.5.4PropertiesofErrorInstances19.5.5NativeErrorTypesUsedinThisStandard19.5.5.1EvalError19.5.5.2RangeError19.5.5.3ReferenceError19.5.5.4SyntaxError19.5.5.5TypeError19.5.5.6URIError

19.5.6NativeErrorObjectStructure19.5.6.1NativeErrorConstructors19.5.6.1.1NativeError(message)

19.5.6.2PropertiesoftheNativeErrorConstructors19.5.6.2.1NativeError.prototype

19.5.6.3PropertiesoftheNativeErrorPrototypeObjects19.5.6.3.1NativeError.prototype.constructor19.5.6.3.2NativeError.prototype.message19.5.6.3.3NativeError.prototype.name

19.5.6.4PropertiesofNativeErrorInstances20NumbersandDates20.1NumberObjects20.1.1TheNumberConstructor20.1.1.1Number(value)

20.1.2PropertiesoftheNumberConstructor20.1.2.1Number.EPSILON20.1.2.2Number.isFinite(number)20.1.2.3Number.isInteger(number)20.1.2.4Number.isNaN(number)20.1.2.5Number.isSafeInteger(number)20.1.2.6Number.MAX_SAFE_INTEGER20.1.2.7Number.MAX_VALUE20.1.2.8Number.MIN_SAFE_INTEGER20.1.2.9Number.MIN_VALUE20.1.2.10Number.NaN20.1.2.11Number.NEGATIVE_INFINITY20.1.2.12Number.parseFloat(string)

20.1.2.13Number.parseInt(string,radix)20.1.2.14Number.POSITIVE_INFINITY20.1.2.15Number.prototype

20.1.3PropertiesoftheNumberPrototypeObject20.1.3.1Number.prototype.constructor20.1.3.2Number.prototype.toExponential(fractionDigits)20.1.3.3Number.prototype.toFixed(fractionDigits)20.1.3.4Number.prototype.toLocaleString([reserved1[,reserved2]])20.1.3.5Number.prototype.toPrecision(precision)20.1.3.6Number.prototype.toString([radix])20.1.3.7Number.prototype.valueOf()

20.1.4PropertiesofNumberInstances20.2TheMathObject20.2.1ValuePropertiesoftheMathObject20.2.1.1Math.E20.2.1.2Math.LN1020.2.1.3Math.LN220.2.1.4Math.LOG10E20.2.1.5Math.LOG2E20.2.1.6Math.PI20.2.1.7Math.SQRT1_220.2.1.8Math.SQRT220.2.1.9Math[@@toStringTag]

20.2.2FunctionPropertiesoftheMathObject20.2.2.1Math.abs(x)20.2.2.2Math.acos(x)20.2.2.3Math.acosh(x)20.2.2.4Math.asin(x)20.2.2.5Math.asinh(x)20.2.2.6Math.atan(x)20.2.2.7Math.atanh(x)20.2.2.8Math.atan2(y,x)20.2.2.9Math.cbrt(x)20.2.2.10Math.ceil(x)20.2.2.11Math.clz32(x)20.2.2.12Math.cos(x)20.2.2.13Math.cosh(x)20.2.2.14Math.exp(x)20.2.2.15Math.expm1(x)20.2.2.16Math.loor(x)

20.2.2.17Math.fround(x)20.2.2.18Math.hypot(value1,value2,...values)20.2.2.19Math.imul(x,y)20.2.2.20Math.log(x)20.2.2.21Math.log1p(x)20.2.2.22Math.log10(x)20.2.2.23Math.log2(x)20.2.2.24Math.max(value1,value2,...values)20.2.2.25Math.min(value1,value2,...values)20.2.2.26Math.pow(base,exponent)20.2.2.27Math.random()20.2.2.28Math.round(x)20.2.2.29Math.sign(x)20.2.2.30Math.sin(x)20.2.2.31Math.sinh(x)20.2.2.32Math.sqrt(x)20.2.2.33Math.tan(x)20.2.2.34Math.tanh(x)20.2.2.35Math.trunc(x)

20.3DateObjects20.3.1OverviewofDateObjectsandDeinitionsofAbstractOperations20.3.1.1TimeValuesandTimeRange20.3.1.2DayNumberandTimewithinDay20.3.1.3YearNumber20.3.1.4MonthNumber20.3.1.5DateNumber20.3.1.6WeekDay20.3.1.7LocalTimeZoneAdjustment20.3.1.8DaylightSavingTimeAdjustment20.3.1.9LocalTime(t)20.3.1.10UTC(t)20.3.1.11Hours,Minutes,Second,andMilliseconds20.3.1.12MakeTime(hour,min,sec,ms)20.3.1.13MakeDay(year,month,date)20.3.1.14MakeDate(day,time)20.3.1.15TimeClip(time)20.3.1.16DateTimeStringFormat20.3.1.16.1ExtendedYears

20.3.2TheDateConstructor20.3.2.1Date(year,month[,date[,hours[,minutes[,seconds[,ms]]]]])

20.3.2.2Date(value)20.3.2.3Date()

20.3.3PropertiesoftheDateConstructor20.3.3.1Date.now()20.3.3.2Date.parse(string)20.3.3.3Date.prototype20.3.3.4Date.UTC(year[,month[,date[,hours[,minutes[,seconds[,ms]]]]]])

20.3.4PropertiesoftheDatePrototypeObject20.3.4.1Date.prototype.constructor20.3.4.2Date.prototype.getDate()20.3.4.3Date.prototype.getDay()20.3.4.4Date.prototype.getFullYear()20.3.4.5Date.prototype.getHours()20.3.4.6Date.prototype.getMilliseconds()20.3.4.7Date.prototype.getMinutes()20.3.4.8Date.prototype.getMonth()20.3.4.9Date.prototype.getSeconds()20.3.4.10Date.prototype.getTime()20.3.4.11Date.prototype.getTimezoneOffset()20.3.4.12Date.prototype.getUTCDate()20.3.4.13Date.prototype.getUTCDay()20.3.4.14Date.prototype.getUTCFullYear()20.3.4.15Date.prototype.getUTCHours()20.3.4.16Date.prototype.getUTCMilliseconds()20.3.4.17Date.prototype.getUTCMinutes()20.3.4.18Date.prototype.getUTCMonth()20.3.4.19Date.prototype.getUTCSeconds()20.3.4.20Date.prototype.setDate(date)20.3.4.21Date.prototype.setFullYear(year[,month[,date]])20.3.4.22Date.prototype.setHours(hour[,min[,sec[,ms]]])20.3.4.23Date.prototype.setMilliseconds(ms)20.3.4.24Date.prototype.setMinutes(min[,sec[,ms]])20.3.4.25Date.prototype.setMonth(month[,date])20.3.4.26Date.prototype.setSeconds(sec[,ms])20.3.4.27Date.prototype.setTime(time)20.3.4.28Date.prototype.setUTCDate(date)20.3.4.29Date.prototype.setUTCFullYear(year[,month[,date]])20.3.4.30Date.prototype.setUTCHours(hour[,min[,sec[,ms]]])20.3.4.31Date.prototype.setUTCMilliseconds(ms)20.3.4.32Date.prototype.setUTCMinutes(min[,sec[,ms]])

20.3.4.33Date.prototype.setUTCMonth(month[,date])20.3.4.34Date.prototype.setUTCSeconds(sec[,ms])20.3.4.35Date.prototype.toDateString()20.3.4.36Date.prototype.toISOString()20.3.4.37Date.prototype.toJSON(key)20.3.4.38Date.prototype.toLocaleDateString([reserved1[,reserved2]])20.3.4.39Date.prototype.toLocaleString([reserved1[,reserved2]])20.3.4.40Date.prototype.toLocaleTimeString([reserved1[,reserved2]])20.3.4.41Date.prototype.toString()20.3.4.41.1RS:ToDateString(tv)

20.3.4.42Date.prototype.toTimeString()20.3.4.43Date.prototype.toUTCString()20.3.4.44Date.prototype.valueOf()20.3.4.45Date.prototype[@@toPrimitive](hint)

20.3.5PropertiesofDateInstances21TextProcessing21.1StringObjects21.1.1TheStringConstructor21.1.1.1String(value)

21.1.2PropertiesoftheStringConstructor21.1.2.1String.fromCharCode(...codeUnits)21.1.2.2String.fromCodePoint(...codePoints)21.1.2.3String.prototype21.1.2.4String.raw(template,...substitutions)

21.1.3PropertiesoftheStringPrototypeObject21.1.3.1String.prototype.charAt(pos)21.1.3.2String.prototype.charCodeAt(pos)21.1.3.3String.prototype.codePointAt(pos)21.1.3.4String.prototype.concat(...args)21.1.3.5String.prototype.constructor21.1.3.6String.prototype.endsWith(searchString[,endPosition])21.1.3.7String.prototype.includes(searchString[,position])21.1.3.8String.prototype.indexOf(searchString[,position])21.1.3.9String.prototype.lastIndexOf(searchString[,position])21.1.3.10String.prototype.localeCompare(that[,reserved1[,reserved2]])21.1.3.11String.prototype.match(regexp)21.1.3.12String.prototype.normalize([form])21.1.3.13String.prototype.padEnd(maxLength[,illString])21.1.3.14String.prototype.padStart(maxLength[,illString])21.1.3.15String.prototype.repeat(count)

21.1.3.16String.prototype.replace(searchValue,replaceValue)21.1.3.16.1RS:GetSubstitution(matched,str,position,captures,replacement)

21.1.3.17String.prototype.search(regexp)21.1.3.18String.prototype.slice(start,end)21.1.3.19String.prototype.split(separator,limit)21.1.3.19.1RS:SplitMatch(S,q,R)

21.1.3.20String.prototype.startsWith(searchString[,position])21.1.3.21String.prototype.substring(start,end)21.1.3.22String.prototype.toLocaleLowerCase([reserved1[,reserved2]])21.1.3.23String.prototype.toLocaleUpperCase([reserved1[,reserved2]])21.1.3.24String.prototype.toLowerCase()21.1.3.25String.prototype.toString()21.1.3.26String.prototype.toUpperCase()21.1.3.27String.prototype.trim()21.1.3.28String.prototype.valueOf()21.1.3.29String.prototype[@@iterator]()

21.1.4PropertiesofStringInstances21.1.4.1length

21.1.5StringIteratorObjects21.1.5.1CreateStringIterator(string)21.1.5.2The%StringIteratorPrototype%Object21.1.5.2.1%StringIteratorPrototype%.next()21.1.5.2.2%StringIteratorPrototype%[@@toStringTag]

21.1.5.3PropertiesofStringIteratorInstances21.2RegExp(RegularExpression)Objects21.2.1Patterns21.2.1.1SS:EarlyErrors

21.2.2PatternSemantics21.2.2.1Notation21.2.2.2Pattern21.2.2.3Disjunction21.2.2.4Alternative21.2.2.5Term21.2.2.5.1RS:RepeatMatcher(m,min,max,greedy,x,c,parenIndex,parenCount)

21.2.2.6Assertion21.2.2.6.1RS:WordCharacters()21.2.2.6.2RS:IsWordChar(e)

21.2.2.7Quantiier21.2.2.8Atom21.2.2.8.1RS:CharacterSetMatcher(A,invert)

21.2.2.8.2RS:Canonicalize(ch)21.2.2.9AtomEscape21.2.2.10CharacterEscape21.2.2.11DecimalEscape21.2.2.12CharacterClassEscape21.2.2.13CharacterClass21.2.2.14ClassRanges21.2.2.15NonemptyClassRanges21.2.2.15.1RS:CharacterRange(A,B)

21.2.2.16NonemptyClassRangesNoDash21.2.2.17ClassAtom21.2.2.18ClassAtomNoDash21.2.2.19ClassEscape

21.2.3TheRegExpConstructor21.2.3.1RegExp(pattern,lags)21.2.3.2AbstractOperationsfortheRegExpConstructor21.2.3.2.1RS:RegExpAlloc(newTarget)21.2.3.2.2RS:RegExpInitialize(obj,pattern,lags)21.2.3.2.3RS:RegExpCreate(P,F)21.2.3.2.4RS:EscapeRegExpPattern(P,F)

21.2.4PropertiesoftheRegExpConstructor21.2.4.1RegExp.prototype21.2.4.2getRegExp[@@species]

21.2.5PropertiesoftheRegExpPrototypeObject21.2.5.1RegExp.prototype.constructor21.2.5.2RegExp.prototype.exec(string)21.2.5.2.1RS:RegExpExec(R,S)21.2.5.2.2RS:RegExpBuiltinExec(R,S)21.2.5.2.3AdvanceStringIndex(S,index,unicode)

21.2.5.3getRegExp.prototype.lags21.2.5.4getRegExp.prototype.global21.2.5.5getRegExp.prototype.ignoreCase21.2.5.6RegExp.prototype[@@match](string)21.2.5.7getRegExp.prototype.multiline21.2.5.8RegExp.prototype[@@replace](string,replaceValue)21.2.5.9RegExp.prototype[@@search](string)21.2.5.10getRegExp.prototype.source21.2.5.11RegExp.prototype[@@split](string,limit)21.2.5.12getRegExp.prototype.sticky21.2.5.13RegExp.prototype.test(S)

21.2.5.14RegExp.prototype.toString()21.2.5.15getRegExp.prototype.unicode

21.2.6PropertiesofRegExpInstances21.2.6.1lastIndex

22IndexedCollections22.1ArrayObjects22.1.1TheArrayConstructor22.1.1.1Array()22.1.1.2Array(len)22.1.1.3Array(...items)

22.1.2PropertiesoftheArrayConstructor22.1.2.1Array.from(items[,mapfn[,thisArg]])22.1.2.2Array.isArray(arg)22.1.2.3Array.of(...items)22.1.2.4Array.prototype22.1.2.5getArray[@@species]

22.1.3PropertiesoftheArrayPrototypeObject22.1.3.1Array.prototype.concat(...arguments)22.1.3.1.1RS:IsConcatSpreadable(O)

22.1.3.2Array.prototype.constructor22.1.3.3Array.prototype.copyWithin(target,start[,end])22.1.3.4Array.prototype.entries()22.1.3.5Array.prototype.every(callbackfn[,thisArg])22.1.3.6Array.prototype.ill(value[,start[,end]])22.1.3.7Array.prototype.ilter(callbackfn[,thisArg])22.1.3.8Array.prototype.ind(predicate[,thisArg])22.1.3.9Array.prototype.indIndex(predicate[,thisArg])22.1.3.10Array.prototype.forEach(callbackfn[,thisArg])22.1.3.11Array.prototype.includes(searchElement[,fromIndex])22.1.3.12Array.prototype.indexOf(searchElement[,fromIndex])22.1.3.13Array.prototype.join(separator)22.1.3.14Array.prototype.keys()22.1.3.15Array.prototype.lastIndexOf(searchElement[,fromIndex])22.1.3.16Array.prototype.map(callbackfn[,thisArg])22.1.3.17Array.prototype.pop()22.1.3.18Array.prototype.push(...items)22.1.3.19Array.prototype.reduce(callbackfn[,initialValue])22.1.3.20Array.prototype.reduceRight(callbackfn[,initialValue])22.1.3.21Array.prototype.reverse()22.1.3.22Array.prototype.shift()

22.1.3.23Array.prototype.slice(start,end)22.1.3.24Array.prototype.some(callbackfn[,thisArg])22.1.3.25Array.prototype.sort(comparefn)22.1.3.25.1RS:SortCompare(x,y)

22.1.3.26Array.prototype.splice(start,deleteCount,...items)22.1.3.27Array.prototype.toLocaleString([reserved1[,reserved2]])22.1.3.28Array.prototype.toString()22.1.3.29Array.prototype.unshift(...items)22.1.3.30Array.prototype.values()22.1.3.31Array.prototype[@@iterator]()22.1.3.32Array.prototype[@@unscopables]

22.1.4PropertiesofArrayInstances22.1.4.1length

22.1.5ArrayIteratorObjects22.1.5.1CreateArrayIterator(array,kind)22.1.5.2The%ArrayIteratorPrototype%Object22.1.5.2.1%ArrayIteratorPrototype%.next()22.1.5.2.2%ArrayIteratorPrototype%[@@toStringTag]

22.1.5.3PropertiesofArrayIteratorInstances22.2TypedArrayObjects22.2.1The%TypedArray%IntrinsicObject22.2.1.1%TypedArray%()

22.2.2Propertiesofthe%TypedArray%IntrinsicObject22.2.2.1%TypedArray%.from(source[,mapfn[,thisArg]])22.2.2.1.1RS:IterableToList(items,method)

22.2.2.2%TypedArray%.of(...items)22.2.2.3%TypedArray%.prototype22.2.2.4get%TypedArray%[@@species]

22.2.3Propertiesofthe%TypedArrayPrototype%Object22.2.3.1get%TypedArray%.prototype.buffer22.2.3.2get%TypedArray%.prototype.byteLength22.2.3.3get%TypedArray%.prototype.byteOffset22.2.3.4%TypedArray%.prototype.constructor22.2.3.5%TypedArray%.prototype.copyWithin(target,start[,end])22.2.3.5.1RS:ValidateTypedArray(O)

22.2.3.6%TypedArray%.prototype.entries()22.2.3.7%TypedArray%.prototype.every(callbackfn[,thisArg])22.2.3.8%TypedArray%.prototype.ill(value[,start[,end]])22.2.3.9%TypedArray%.prototype.ilter(callbackfn[,thisArg])22.2.3.10%TypedArray%.prototype.ind(predicate[,thisArg])

22.2.3.11%TypedArray%.prototype.indIndex(predicate[,thisArg])22.2.3.12%TypedArray%.prototype.forEach(callbackfn[,thisArg])22.2.3.13%TypedArray%.prototype.includes(searchElement[,fromIndex])22.2.3.14%TypedArray%.prototype.indexOf(searchElement[,fromIndex])22.2.3.15%TypedArray%.prototype.join(separator)22.2.3.16%TypedArray%.prototype.keys()22.2.3.17%TypedArray%.prototype.lastIndexOf(searchElement[,fromIndex])22.2.3.18get%TypedArray%.prototype.length22.2.3.19%TypedArray%.prototype.map(callbackfn[,thisArg])22.2.3.20%TypedArray%.prototype.reduce(callbackfn[,initialValue])22.2.3.21%TypedArray%.prototype.reduceRight(callbackfn[,initialValue])22.2.3.22%TypedArray%.prototype.reverse()22.2.3.23%TypedArray%.prototype.set(overloaded[,offset])22.2.3.23.1%TypedArray%.prototype.set(array[,offset])22.2.3.23.2%TypedArray%.prototype.set(typedArray[,offset])

22.2.3.24%TypedArray%.prototype.slice(start,end)22.2.3.25%TypedArray%.prototype.some(callbackfn[,thisArg])22.2.3.26%TypedArray%.prototype.sort(comparefn)22.2.3.27%TypedArray%.prototype.subarray(begin,end)22.2.3.28%TypedArray%.prototype.toLocaleString([reserved1[,reserved2]])22.2.3.29%TypedArray%.prototype.toString()22.2.3.30%TypedArray%.prototype.values()22.2.3.31%TypedArray%.prototype[@@iterator]()22.2.3.32get%TypedArray%.prototype[@@toStringTag]

22.2.4TheTypedArrayConstructors22.2.4.1TypedArray()22.2.4.2TypedArray(length)22.2.4.2.1RS:AllocateTypedArray(constructorName,newTarget,defaultProto[,length])22.2.4.2.2RS:AllocateTypedArrayBuffer(O,length)

22.2.4.3TypedArray(typedArray)22.2.4.4TypedArray(object)22.2.4.5TypedArray(buffer[,byteOffset[,length]])22.2.4.6TypedArrayCreate(constructor,argumentList)22.2.4.7TypedArraySpeciesCreate(exemplar,argumentList)

22.2.5PropertiesoftheTypedArrayConstructors22.2.5.1TypedArray.BYTES_PER_ELEMENT22.2.5.2TypedArray.prototype

22.2.6PropertiesofTypedArrayPrototypeObjects22.2.6.1TypedArray.prototype.BYTES_PER_ELEMENT22.2.6.2TypedArray.prototype.constructor

22.2.7PropertiesofTypedArrayInstances23KeyedCollection23.1MapObjects23.1.1TheMapConstructor23.1.1.1Map([iterable])

23.1.2PropertiesoftheMapConstructor23.1.2.1Map.prototype23.1.2.2getMap[@@species]

23.1.3PropertiesoftheMapPrototypeObject23.1.3.1Map.prototype.clear()23.1.3.2Map.prototype.constructor23.1.3.3Map.prototype.delete(key)23.1.3.4Map.prototype.entries()23.1.3.5Map.prototype.forEach(callbackfn[,thisArg])23.1.3.6Map.prototype.get(key)23.1.3.7Map.prototype.has(key)23.1.3.8Map.prototype.keys()23.1.3.9Map.prototype.set(key,value)23.1.3.10getMap.prototype.size23.1.3.11Map.prototype.values()23.1.3.12Map.prototype[@@iterator]()23.1.3.13Map.prototype[@@toStringTag]

23.1.4PropertiesofMapInstances23.1.5MapIteratorObjects23.1.5.1CreateMapIterator(map,kind)23.1.5.2The%MapIteratorPrototype%Object23.1.5.2.1%MapIteratorPrototype%.next()23.1.5.2.2%MapIteratorPrototype%[@@toStringTag]

23.1.5.3PropertiesofMapIteratorInstances23.2SetObjects23.2.1TheSetConstructor23.2.1.1Set([iterable])

23.2.2PropertiesoftheSetConstructor23.2.2.1Set.prototype23.2.2.2getSet[@@species]

23.2.3PropertiesoftheSetPrototypeObject23.2.3.1Set.prototype.add(value)23.2.3.2Set.prototype.clear()23.2.3.3Set.prototype.constructor23.2.3.4Set.prototype.delete(value)

23.2.3.5Set.prototype.entries()23.2.3.6Set.prototype.forEach(callbackfn[,thisArg])23.2.3.7Set.prototype.has(value)23.2.3.8Set.prototype.keys()23.2.3.9getSet.prototype.size23.2.3.10Set.prototype.values()23.2.3.11Set.prototype[@@iterator]()23.2.3.12Set.prototype[@@toStringTag]

23.2.4PropertiesofSetInstances23.2.5SetIteratorObjects23.2.5.1CreateSetIterator(set,kind)23.2.5.2The%SetIteratorPrototype%Object23.2.5.2.1%SetIteratorPrototype%.next()23.2.5.2.2%SetIteratorPrototype%[@@toStringTag]

23.2.5.3PropertiesofSetIteratorInstances23.3WeakMapObjects23.3.1TheWeakMapConstructor23.3.1.1WeakMap([iterable])

23.3.2PropertiesoftheWeakMapConstructor23.3.2.1WeakMap.prototype

23.3.3PropertiesoftheWeakMapPrototypeObject23.3.3.1WeakMap.prototype.constructor23.3.3.2WeakMap.prototype.delete(key)23.3.3.3WeakMap.prototype.get(key)23.3.3.4WeakMap.prototype.has(key)23.3.3.5WeakMap.prototype.set(key,value)23.3.3.6WeakMap.prototype[@@toStringTag]

23.3.4PropertiesofWeakMapInstances23.4WeakSetObjects23.4.1TheWeakSetConstructor23.4.1.1WeakSet([iterable])

23.4.2PropertiesoftheWeakSetConstructor23.4.2.1WeakSet.prototype

23.4.3PropertiesoftheWeakSetPrototypeObject23.4.3.1WeakSet.prototype.add(value)23.4.3.2WeakSet.prototype.constructor23.4.3.3WeakSet.prototype.delete(value)23.4.3.4WeakSet.prototype.has(value)23.4.3.5WeakSet.prototype[@@toStringTag]

23.4.4PropertiesofWeakSetInstances

24StructuredData24.1ArrayBufferObjects24.1.1AbstractOperationsForArrayBufferObjects24.1.1.1AllocateArrayBuffer(constructor,byteLength)24.1.1.2IsDetachedBuffer(arrayBuffer)24.1.1.3DetachArrayBuffer(arrayBuffer)24.1.1.4CloneArrayBuffer(srcBuffer,srcByteOffset,srcLength[,cloneConstructor])24.1.1.5RawBytesToNumber(type,rawBytes,isLittleEndian)24.1.1.6GetValueFromBuffer(arrayBuffer,byteIndex,type,isTypedArray,order[,isLittleEndian])24.1.1.7NumberToRawBytes(type,value,isLittleEndian)24.1.1.8SetValueInBuffer(arrayBuffer,byteIndex,type,value,isTypedArray,order[,isLittleEndian])24.1.1.9GetModifySetValueInBuffer(arrayBuffer,byteIndex,type,value,op[,isLittleEndian])

24.1.2TheArrayBufferConstructor24.1.2.1ArrayBuffer(length)

24.1.3PropertiesoftheArrayBufferConstructor24.1.3.1ArrayBuffer.isView(arg)24.1.3.2ArrayBuffer.prototype24.1.3.3getArrayBuffer[@@species]

24.1.4PropertiesoftheArrayBufferPrototypeObject24.1.4.1getArrayBuffer.prototype.byteLength24.1.4.2ArrayBuffer.prototype.constructor24.1.4.3ArrayBuffer.prototype.slice(start,end)24.1.4.4ArrayBuffer.prototype[@@toStringTag]

24.1.5PropertiesoftheArrayBufferInstances24.2SharedArrayBufferObjects24.2.1AbstractOperationsforSharedArrayBufferObjects24.2.1.1AllocateSharedArrayBuffer(constructor,byteLength)24.2.1.2IsSharedArrayBuffer(obj)

24.2.2TheSharedArrayBufferConstructor24.2.2.1SharedArrayBuffer(length)

24.2.3PropertiesoftheSharedArrayBufferConstructor24.2.3.1SharedArrayBuffer.prototype24.2.3.2getSharedArrayBuffer[@@species]

24.2.4PropertiesoftheSharedArrayBufferPrototypeObject24.2.4.1getSharedArrayBuffer.prototype.byteLength24.2.4.2SharedArrayBuffer.prototype.constructor24.2.4.3SharedArrayBuffer.prototype.slice(start,end)24.2.4.4SharedArrayBuffer.prototype[@@toStringTag]

24.2.5PropertiesoftheSharedArrayBufferInstances

24.3DataViewObjects24.3.1AbstractOperationsForDataViewObjects24.3.1.1GetViewValue(view,requestIndex,isLittleEndian,type)24.3.1.2SetViewValue(view,requestIndex,isLittleEndian,type,value)

24.3.2TheDataViewConstructor24.3.2.1DataView(buffer[,byteOffset[,byteLength]])

24.3.3PropertiesoftheDataViewConstructor24.3.3.1DataView.prototype

24.3.4PropertiesoftheDataViewPrototypeObject24.3.4.1getDataView.prototype.buffer24.3.4.2getDataView.prototype.byteLength24.3.4.3getDataView.prototype.byteOffset24.3.4.4DataView.prototype.constructor24.3.4.5DataView.prototype.getFloat32(byteOffset[,littleEndian])24.3.4.6DataView.prototype.getFloat64(byteOffset[,littleEndian])24.3.4.7DataView.prototype.getInt8(byteOffset)24.3.4.8DataView.prototype.getInt16(byteOffset[,littleEndian])24.3.4.9DataView.prototype.getInt32(byteOffset[,littleEndian])24.3.4.10DataView.prototype.getUint8(byteOffset)24.3.4.11DataView.prototype.getUint16(byteOffset[,littleEndian])24.3.4.12DataView.prototype.getUint32(byteOffset[,littleEndian])24.3.4.13DataView.prototype.setFloat32(byteOffset,value[,littleEndian])24.3.4.14DataView.prototype.setFloat64(byteOffset,value[,littleEndian])24.3.4.15DataView.prototype.setInt8(byteOffset,value)24.3.4.16DataView.prototype.setInt16(byteOffset,value[,littleEndian])24.3.4.17DataView.prototype.setInt32(byteOffset,value[,littleEndian])24.3.4.18DataView.prototype.setUint8(byteOffset,value)24.3.4.19DataView.prototype.setUint16(byteOffset,value[,littleEndian])24.3.4.20DataView.prototype.setUint32(byteOffset,value[,littleEndian])24.3.4.21DataView.prototype[@@toStringTag]

24.3.5PropertiesofDataViewInstances24.4TheAtomicsObject24.4.1AbstractOperationsforAtomics24.4.1.1ValidateSharedIntegerTypedArray(typedArray[,onlyInt32])24.4.1.2ValidateAtomicAccess(typedArray,requestIndex)24.4.1.3GetWaiterList(block,i)24.4.1.4EnterCriticalSection(WL)24.4.1.5LeaveCriticalSection(WL)24.4.1.6AddWaiter(WL,W)24.4.1.7RemoveWaiter(WL,W)

24.4.1.8RemoveWaiters(WL,c)24.4.1.9Suspend(WL,W,timeout)24.4.1.10WakeWaiter(WL,W)24.4.1.11AtomicReadModifyWrite(typedArray,index,value,op)24.4.1.12AtomicLoad(typedArray,index)

24.4.2Atomics.add(typedArray,index,value)24.4.3Atomics.and(typedArray,index,value)24.4.4Atomics.compareExchange(typedArray,index,expectedValue,replacementValue)24.4.5Atomics.exchange(typedArray,index,value)24.4.6Atomics.isLockFree(size)24.4.7Atomics.load(typedArray,index)24.4.8Atomics.or(typedArray,index,value)24.4.9Atomics.store(typedArray,index,value)24.4.10Atomics.sub(typedArray,index,value)24.4.11Atomics.wait(typedArray,index,value,timeout)24.4.12Atomics.wake(typedArray,index,count)24.4.13Atomics.xor(typedArray,index,value)24.4.14Atomics[@@toStringTag]

24.5TheJSONObject24.5.1JSON.parse(text[,reviver])24.5.1.1RS:InternalizeJSONProperty(holder,name)

24.5.2JSON.stringify(value[,replacer[,space]])24.5.2.1RS:SerializeJSONProperty(key,holder)24.5.2.2RS:QuoteJSONString(value)24.5.2.3RS:SerializeJSONObject(value)24.5.2.4RS:SerializeJSONArray(value)

24.5.3JSON[@@toStringTag]25ControlAbstractionObjects25.1Iteration25.1.1CommonIterationInterfaces25.1.1.1TheIterableInterface25.1.1.2TheIteratorInterface25.1.1.3TheIteratorResultInterface

25.1.2The%IteratorPrototype%Object25.1.2.1%IteratorPrototype%[@@iterator]()

25.2GeneratorFunctionObjects25.2.1TheGeneratorFunctionConstructor25.2.1.1GeneratorFunction(p1,p2,,pn,body)

25.2.2PropertiesoftheGeneratorFunctionConstructor25.2.2.1GeneratorFunction.length

25.2.2.2GeneratorFunction.prototype25.2.3PropertiesoftheGeneratorFunctionPrototypeObject25.2.3.1GeneratorFunction.prototype.constructor25.2.3.2GeneratorFunction.prototype.prototype25.2.3.3GeneratorFunction.prototype[@@toStringTag]

25.2.4GeneratorFunctionInstances25.2.4.1length25.2.4.2name25.2.4.3prototype

25.3GeneratorObjects25.3.1PropertiesofGeneratorPrototype25.3.1.1Generator.prototype.constructor25.3.1.2Generator.prototype.next(value)25.3.1.3Generator.prototype.return(value)25.3.1.4Generator.prototype.throw(exception)25.3.1.5Generator.prototype[@@toStringTag]

25.3.2PropertiesofGeneratorInstances25.3.3GeneratorAbstractOperations25.3.3.1GeneratorStart(generator,generatorBody)25.3.3.2GeneratorValidate(generator)25.3.3.3GeneratorResume(generator,value)25.3.3.4GeneratorResumeAbrupt(generator,abruptCompletion)25.3.3.5GeneratorYield(iterNextObj)

25.4PromiseObjects25.4.1PromiseAbstractOperations25.4.1.1PromiseCapabilityRecords25.4.1.1.1IfAbruptRejectPromise(value,capability)

25.4.1.2PromiseReactionRecords25.4.1.3CreateResolvingFunctions(promise)25.4.1.3.1PromiseRejectFunctions25.4.1.3.2PromiseResolveFunctions

25.4.1.4FulillPromise(promise,value)25.4.1.5NewPromiseCapability(C)25.4.1.5.1GetCapabilitiesExecutorFunctions

25.4.1.6IsPromise(x)25.4.1.7RejectPromise(promise,reason)25.4.1.8TriggerPromiseReactions(reactions,argument)25.4.1.9HostPromiseRejectionTracker(promise,operation)

25.4.2PromiseJobs25.4.2.1PromiseReactionJob(reaction,argument)

25.4.2.2PromiseResolveThenableJob(promiseToResolve,thenable,then)25.4.3ThePromiseConstructor25.4.3.1Promise(executor)

25.4.4PropertiesofthePromiseConstructor25.4.4.1Promise.all(iterable)25.4.4.1.1RS:PerformPromiseAll(iteratorRecord,constructor,resultCapability)25.4.4.1.2Promise.allResolveElementFunctions

25.4.4.2Promise.prototype25.4.4.3Promise.race(iterable)25.4.4.3.1RS:PerformPromiseRace(iteratorRecord,constructor,resultCapability)

25.4.4.4Promise.reject(r)25.4.4.5Promise.resolve(x)25.4.4.6getPromise[@@species]

25.4.5PropertiesofthePromisePrototypeObject25.4.5.1Promise.prototype.catch(onRejected)25.4.5.2Promise.prototype.constructor25.4.5.3Promise.prototype.then(onFulilled,onRejected)25.4.5.3.1PerformPromiseThen(promise,onFulilled,onRejected,resultCapability)

25.4.5.4Promise.prototype[@@toStringTag]25.4.6PropertiesofPromiseInstances

25.5AsyncFunctionObjects25.5.1TheAsyncFunctionConstructor25.5.1.1AsyncFunction(p1,p2,,pn,body)

25.5.2PropertiesoftheAsyncFunctionConstructor25.5.2.1AsyncFunction.length25.5.2.2AsyncFunction.prototype

25.5.3PropertiesoftheAsyncFunctionPrototypeObject25.5.3.1AsyncFunction.prototype.constructor25.5.3.2AsyncFunction.prototype[@@toStringTag]

25.5.4AsyncFunctionInstances25.5.4.1length25.5.4.2name

25.5.5AsyncFunctionsAbstractOperations25.5.5.1AsyncFunctionCreate(kind,parameters,body,Scope,Strict)25.5.5.2AsyncFunctionStart(promiseCapability,asyncFunctionBody)25.5.5.3AsyncFunctionAwait(value)25.5.5.4AsyncFunctionAwaitedFulilled25.5.5.5AsyncFunctionAwaitedRejected

26Relection26.1TheRelectObject

26.1.1Relect.apply(target,thisArgument,argumentsList)26.1.2Relect.construct(target,argumentsList[,newTarget])26.1.3Relect.deineProperty(target,propertyKey,attributes)26.1.4Relect.deleteProperty(target,propertyKey)26.1.5Relect.get(target,propertyKey[,receiver])26.1.6Relect.getOwnPropertyDescriptor(target,propertyKey)26.1.7Relect.getPrototypeOf(target)26.1.8Relect.has(target,propertyKey)26.1.9Relect.isExtensible(target)26.1.10Relect.ownKeys(target)26.1.11Relect.preventExtensions(target)26.1.12Relect.set(target,propertyKey,V[,receiver])26.1.13Relect.setPrototypeOf(target,proto)

26.2ProxyObjects26.2.1TheProxyConstructor26.2.1.1Proxy(target,handler)

26.2.2PropertiesoftheProxyConstructor26.2.2.1Proxy.revocable(target,handler)26.2.2.1.1ProxyRevocationFunctions

26.3ModuleNamespaceObjects26.3.1@@toStringTag

27MemoryModel27.1MemoryModelFundamentals27.2AgentEventsRecords27.3ChosenValueRecords27.4CandidateExecutions27.5AbstractOperationsfortheMemoryModel27.5.1EventSet(execution)27.5.2SharedDataBlockEventSet(execution)27.5.3HostEventSet(execution)27.5.4ComposeWriteEventBytes(execution,byteIndex,Ws)27.5.5ValueOfReadEvent(execution,R)

27.6RelationsofCandidateExecutions27.6.1agentorder27.6.2readsbytesfrom27.6.3readsfrom27.6.4hostsynchronizeswith27.6.5synchronizeswith27.6.6happensbefore

27.7PropertiesofValidExecutions

27.7.1ValidChosenReads27.7.2CoherentReads27.7.3TearFreeReads27.7.4SequentiallyConsistentAtomics27.7.5ValidExecutions

27.8Races27.9DataRaces27.10DataRaceFreedom27.11SharedMemoryGuidelines

AGrammarSummaryA.1LexicalGrammarA.2ExpressionsA.3StatementsA.4FunctionsandClassesA.5ScriptsandModulesA.6NumberConversionsA.7UniversalResourceIdentiierCharacterClassesA.8RegularExpressions

BAdditionalECMAScriptFeaturesforWebBrowsersB.1AdditionalSyntaxB.1.1NumericLiteralsB.1.1.1StaticSemantics

B.1.2StringLiteralsB.1.2.1StaticSemantics

B.1.3HTMLlikeCommentsB.1.4RegularExpressionsPatternsB.1.4.1PatternSemanticsB.1.4.1.1RS:CharacterRangeOrUnion(A,B)

B.2AdditionalBuiltinPropertiesB.2.1AdditionalPropertiesoftheGlobalObjectB.2.1.1escape(string)B.2.1.2unescape(string)

B.2.2AdditionalPropertiesoftheObject.prototypeObjectB.2.2.1Object.prototype.__proto__B.2.2.1.1getObject.prototype.__proto__B.2.2.1.2setObject.prototype.__proto__

B.2.2.2Object.prototype.__deineGetter__(P,getter)B.2.2.3Object.prototype.__deineSetter__(P,setter)B.2.2.4Object.prototype.__lookupGetter__(P)B.2.2.5Object.prototype.__lookupSetter__(P)

B.2.3AdditionalPropertiesoftheString.prototypeObjectB.2.3.1String.prototype.substr(start,length)B.2.3.2String.prototype.anchor(name)B.2.3.2.1RS:CreateHTML(string,tag,attribute,value)

B.2.3.3String.prototype.big()B.2.3.4String.prototype.blink()B.2.3.5String.prototype.bold()B.2.3.6String.prototype.ixed()B.2.3.7String.prototype.fontcolor(color)B.2.3.8String.prototype.fontsize(size)B.2.3.9String.prototype.italics()B.2.3.10String.prototype.link(url)B.2.3.11String.prototype.small()B.2.3.12String.prototype.strike()B.2.3.13String.prototype.sub()B.2.3.14String.prototype.sup()

B.2.4AdditionalPropertiesoftheDate.prototypeObjectB.2.4.1Date.prototype.getYear()B.2.4.2Date.prototype.setYear(year)B.2.4.3Date.prototype.toGMTString()

B.2.5AdditionalPropertiesoftheRegExp.prototypeObjectB.2.5.1RegExp.prototype.compile(pattern,lags)

B.3OtherAdditionalFeaturesB.3.1__proto__PropertyNamesinObjectInitializersB.3.2LabelledFunctionDeclarationsB.3.3BlockLevelFunctionDeclarationsWebLegacyCompatibilitySemanticsB.3.3.1ChangestoFunctionDeclarationInstantiationB.3.3.2ChangestoGlobalDeclarationInstantiationB.3.3.3ChangestoEvalDeclarationInstantiationB.3.3.4ChangestoBlockSS:EarlyErrorsB.3.3.5ChangestoswitchStatementSS:EarlyErrorsB.3.3.6ChangestoBlockDeclarationInstantiation

B.3.4FunctionDeclarationsinIfStatementStatementClausesB.3.5VariableStatementsinCatchBlocksB.3.6InitializersinForInStatementHeads

CTheStrictModeofECMAScriptDCorrectionsandClariicationsinECMAScript2015withPossibleCompatibilityImpactEAdditionsandChangesThatIntroduceIncompatibilitieswithPriorEditionsFBibliographyGCopyright&SoftwareLicense

Introduction

ThisEcmaStandarddeinestheECMAScript2017Language.ItistheeightheditionoftheECMAScriptLanguageSpeciication.Sincepublicationoftheirsteditionin1997,ECMAScripthasgrowntobeoneoftheworld'smostwidelyusedgeneralpurposeprogramminglanguages.Itisbestknownasthelanguageembeddedinwebbrowsersbuthasalsobeenwidelyadoptedforserverandembeddedapplications.

ECMAScriptisbasedonseveraloriginatingtechnologies,themostwellknownbeingJavaScript(Netscape)andJScript(Microsoft).ThelanguagewasinventedbyBrendanEichatNetscapeandirstappearedinthatcompany'sNavigator2.0browser.IthasappearedinallsubsequentbrowsersfromNetscapeandinallbrowsersfromMicrosoftstartingwithInternetExplorer3.0.

ThedevelopmentoftheECMAScriptLanguageSpeciicationstartedinNovember1996.TheirsteditionofthisEcmaStandardwasadoptedbytheEcmaGeneralAssemblyofJune1997.

ThatEcmaStandardwassubmittedtoISO/IECJTC1foradoptionunderthefasttrackprocedure,andapprovedasinternationalstandardISO/IEC16262,inApril1998.TheEcmaGeneralAssemblyofJune1998approvedthesecondeditionofECMA262tokeepitfullyalignedwithISO/IEC16262.Changesbetweentheirstandthesecondeditionareeditorialinnature.

ThethirdeditionoftheStandardintroducedpowerfulregularexpressions,betterstringhandling,newcontrolstatements,try/catchexceptionhandling,tighterdeinitionoferrors,formattingfornumericoutputandminorchangesinanticipationoffuturelanguagegrowth.ThethirdeditionoftheECMAScriptstandardwasadoptedbytheEcmaGeneralAssemblyofDecember1999andpublishedasISO/IEC16262:2002inJune2002.

Afterpublicationofthethirdedition,ECMAScriptachievedmassiveadoptioninconjunctionwiththeWorldWideWebwhereithasbecometheprogramminglanguagethatissupportedbyessentiallyallwebbrowsers.SigniicantworkwasdonetodevelopafourtheditionofECMAScript.However,thatworkwasnotcompletedandnotpublishedasthefourtheditionofECMAScriptbutsomeofitwasincorporatedintothedevelopmentofthesixthedition.

TheiftheditionofECMAScript(publishedasECMA2625thedition)codiieddefactointerpretationsofthelanguagespeciicationthathavebecomecommonamongbrowserimplementationsandaddedsupportfornewfeaturesthathademergedsincethepublicationofthethirdedition.Suchfeaturesincludeaccessorproperties,relectivecreationandinspectionofobjects,programcontrolofpropertyattributes,additionalarraymanipulationfunctions,supportfortheJSONobjectencodingformat,andastrictmodethatprovidesenhancederrorcheckingandprogramsecurity.TheiftheditionwasadoptedbytheEcmaGeneralAssemblyofDecember2009.

TheiftheditionwassubmittedtoISO/IECJTC1foradoptionunderthefasttrackprocedure,andapprovedasinternationalstandardISO/IEC16262:2011.Edition5.1oftheECMAScriptStandard

Introduction

incorporatedminorcorrectionsandisthesametextasISO/IEC16262:2011.The5.1EditionwasadoptedbytheEcmaGeneralAssemblyofJune2011.

Focuseddevelopmentofthesixtheditionstartedin2009,astheiftheditionwasbeingpreparedforpublication.However,thiswasprecededbysigniicantexperimentationandlanguageenhancementdesigneffortsdatingtothepublicationofthethirdeditionin1999.Inaveryrealsense,thecompletionofthesixtheditionistheculminationofaifteenyeareffort.Thegoalsforthisadditionincludedprovidingbettersupportforlargeapplications,librarycreation,andforuseofECMAScriptasacompilationtargetforotherlanguages.Someofitsmajorenhancementsincludedmodules,classdeclarations,lexicalblockscoping,iteratorsandgenerators,promisesforasynchronousprogramming,destructuringpatterns,andpropertailcalls.TheECMAScriptlibraryofbuiltinswasexpandedtosupportadditionaldataabstractionsincludingmaps,sets,andarraysofbinarynumericvaluesaswellasadditionalsupportforUnicodesupplementalcharactersinstringsandregularexpressions.Thebuiltinswerealsomadeextensibleviasubclassing.Thesixtheditionprovidesthefoundationforregular,incrementallanguageandlibraryenhancements.ThesixtheditionwasadoptedbytheGeneralAssemblyofJune2015.

ECMAScript2016wastheirstECMAScripteditionreleasedunderEcmaTC39'snewyearlyreleasecadenceandopendevelopmentprocess.AplaintextsourcedocumentwasbuiltfromtheECMAScript2015sourcedocumenttoserveasthebaseforfurtherdevelopmententirelyonGitHub.Overtheyearofthisstandard'sdevelopment,hundredsofpullrequestsandissueswereiledrepresentingthousandsofbugixes,editorialixesandotherimprovements.Additionally,numeroussoftwaretoolsweredevelopedtoaidinthiseffortincludingEcmarkup,Ecmarkdown,andGrammarkdown.ES2016alsoincludedsupportforanewexponentiationoperatorandaddsanewmethodtoArray.prototypecalledincludes.

ThisspeciicationintroducesAsyncFunctions,SharedMemory,andAtomicsalongwithsmallerlanguageandlibraryenhancements,bugixes,andeditorialupdates.Asyncfunctionsimprovetheasynchronousprogrammingexperiencebyprovidingsyntaxforpromisereturningfunctions.SharedMemoryandAtomicsintroduceanewmemorymodelthatallowsmultiagentprogramstocommunicateusingatomicoperationsthatensureawelldeinedexecutionorderevenonparallelCPUs.ThisspeciicationalsoincludesnewstaticmethodsonObject:Object.values,Object.entries,andObject.getOwnPropertyDescriptors.

DozensofindividualsrepresentingmanyorganizationshavemadeverysigniicantcontributionswithinEcmaTC39tothedevelopmentofthiseditionandtotheprioreditions.Inaddition,avibrantcommunityhasemergedsupportingTC39'sECMAScriptefforts.Thiscommunityhasreviewednumerousdrafts,iledthousandsofbugreports,performedimplementationexperiments,contributedtestsuites,andeducatedtheworldwidedevelopercommunityaboutECMAScript.Unfortunately,itisimpossibletoidentifyandacknowledgeeverypersonandorganizationwhohascontributedtothiseffort.

AllenWirfsBrock

ECMA262,6thEditionProjectEditor

BrianTerlson

ECMA262,7thEditionProjectEditor

ThisStandarddeinestheECMAScript2017generalpurposeprogramminglanguage.

AconformingimplementationofECMAScriptmustprovideandsupportallthetypes,values,objects,properties,functions,andprogramsyntaxandsemanticsdescribedinthisspeciication.

AconformingimplementationofECMAScriptmustinterpretsourcetextinputinconformancewiththelatestversionoftheUnicodeStandardandISO/IEC10646.

AconformingimplementationofECMAScriptthatprovidesanapplicationprogramminginterfacethatsupportsprogramsthatneedtoadapttothelinguisticandculturalconventionsusedbydifferenthumanlanguagesandcountriesmustimplementtheinterfacedeinedbythemostrecenteditionofECMA402thatiscompatiblewiththisspeciication.

AconformingimplementationofECMAScriptmayprovideadditionaltypes,values,objects,properties,andfunctionsbeyondthosedescribedinthisspeciication.Inparticular,aconformingimplementationofECMAScriptmayprovidepropertiesnotdescribedinthisspeciication,andvaluesforthoseproperties,forobjectsthataredescribedinthisspeciication.

AconformingimplementationofECMAScriptmaysupportprogramandregularexpressionsyntaxnotdescribedinthisspeciication.Inparticular,aconformingimplementationofECMAScriptmaysupportprogramsyntaxthatmakesuseofthefuturereservedwordslistedinsubclause11.6.2.2ofthisspeciication.

AconformingimplementationofECMAScriptmustnotimplementanyextensionthatislistedasaForbiddenExtensioninsubclause16.2.

Thefollowingreferenceddocumentsareindispensablefortheapplicationofthisdocument.Fordatedreferences,onlytheeditioncitedapplies.Forundatedreferences,thelatesteditionofthereferenced

1 Scope

2 Conformance

3 NormativeReferences

document(includinganyamendments)applies.

ISO/IEC10646:2003:InformationTechnologyUniversalMultipleOctetCodedCharacterSet(UCS)plusAmendment1:2005,Amendment2:2006,Amendment3:2008,andAmendment4:2008,plusadditionalamendmentsandcorrigenda,orsuccessor

ECMA402,ECMAScript2015InternationalizationAPISpeciication.http://www.ecmainternational.org/publications/standards/Ecma402.htm

ECMA404,TheJSONDataInterchangeFormat.http://www.ecmainternational.org/publications/standards/Ecma404.htm

ThissectioncontainsanonnormativeoverviewoftheECMAScriptlanguage.

ECMAScriptisanobjectorientedprogramminglanguageforperformingcomputationsandmanipulatingcomputationalobjectswithinahostenvironment.ECMAScriptasdeinedhereisnotintendedtobecomputationallyselfsuficient;indeed,therearenoprovisionsinthisspeciicationforinputofexternaldataoroutputofcomputedresults.Instead,itisexpectedthatthecomputationalenvironmentofanECMAScriptprogramwillprovidenotonlytheobjectsandotherfacilitiesdescribedinthisspeciicationbutalsocertainenvironmentspeciicobjects,whosedescriptionandbehaviourarebeyondthescopeofthisspeciicationexcepttoindicatethattheymayprovidecertainpropertiesthatcanbeaccessedandcertainfunctionsthatcanbecalledfromanECMAScriptprogram.

ECMAScriptwasoriginallydesignedtobeusedasascriptinglanguage,buthasbecomewidelyusedasageneralpurposeprogramminglanguage.Ascriptinglanguageisaprogramminglanguagethatisusedtomanipulate,customize,andautomatethefacilitiesofanexistingsystem.Insuchsystems,usefulfunctionalityisalreadyavailablethroughauserinterface,andthescriptinglanguageisamechanismforexposingthatfunctionalitytoprogramcontrol.Inthisway,theexistingsystemissaidtoprovideahostenvironmentofobjectsandfacilities,whichcompletesthecapabilitiesofthescriptinglanguage.Ascriptinglanguageisintendedforusebybothprofessionalandnonprofessionalprogrammers.

ECMAScriptwasoriginallydesignedtobeaWebscriptinglanguage,providingamechanismtoenlivenWebpagesinbrowsersandtoperformservercomputationaspartofaWebbasedclientserverarchitecture.ECMAScriptisnowusedtoprovidecorescriptingcapabilitiesforavarietyofhostenvironments.Thereforethecorelanguageisspeciiedinthisdocumentapartfromanyparticularhostenvironment.

ECMAScriptusagehasmovedbeyondsimplescriptinganditisnowusedforthefullspectrumofprogrammingtasksinmanydifferentenvironmentsandscales.AstheusageofECMAScripthasexpanded,

4 Overview

http://www.ecma-international.org/publications/standards/Ecma-402.htmhttp://www.ecma-international.org/publications/standards/Ecma-404.htm

sohasthefeaturesandfacilitiesitprovides.ECMAScriptisnowafullyfeaturedgeneralpurposeprogramminglanguage.

SomeofthefacilitiesofECMAScriptaresimilartothoseusedinotherprogramminglanguages;inparticularC,Java,Self,andSchemeasdescribedin:

ISO/IEC9899:1996,ProgrammingLanguagesC.

Gosling,James,BillJoyandGuySteele.TheJavaLanguageSpeciication.AddisonWesleyPublishingCo.,1996.

Ungar,David,andSmith,RandallB.Self:ThePowerofSimplicity.OOPSLA'87ConferenceProceedings,pp.227241,Orlando,FL,October1987.

IEEEStandardfortheSchemeProgrammingLanguage.IEEEStd11781990.

AwebbrowserprovidesanECMAScripthostenvironmentforclientsidecomputationincluding,forinstance,objectsthatrepresentwindows,menus,popups,dialogboxes,textareas,anchors,frames,history,cookies,andinput/output.Further,thehostenvironmentprovidesameanstoattachscriptingcodetoeventssuchaschangeoffocus,pageandimageloading,unloading,errorandabort,selection,formsubmission,andmouseactions.ScriptingcodeappearswithintheHTMLandthedisplayedpageisacombinationofuserinterfaceelementsandixedandcomputedtextandimages.Thescriptingcodeisreactivetouserinteraction,andthereisnoneedforamainprogram.

Awebserverprovidesadifferenthostenvironmentforserversidecomputationincludingobjectsrepresentingrequests,clients,andiles;andmechanismstolockandsharedata.Byusingbrowsersideandserversidescriptingtogether,itispossibletodistributecomputationbetweentheclientandserverwhileprovidingacustomizeduserinterfaceforaWebbasedapplication.

EachWebbrowserandserverthatsupportsECMAScriptsuppliesitsownhostenvironment,completingtheECMAScriptexecutionenvironment.

ThefollowingisaninformaloverviewofECMAScriptnotallpartsofthelanguagearedescribed.Thisoverviewisnotpartofthestandardproper.

ECMAScriptisobjectbased:basiclanguageandhostfacilitiesareprovidedbyobjects,andanECMAScriptprogramisaclusterofcommunicatingobjects.InECMAScript,anobjectisacollectionofzeroormore

4.1 WebScripting

4.2 ECMAScriptOverview

propertieseachwithattributesthatdeterminehoweachpropertycanbeusedforexample,whentheWritableattributeforapropertyissettofalse,anyattemptbyexecutedECMAScriptcodetoassignadifferentvaluetothepropertyfails.Propertiesarecontainersthatholdotherobjects,primitivevalues,orfunctions.Aprimitivevalueisamemberofoneofthefollowingbuiltintypes:Undeined,Null,Boolean,Number,String,andSymbol;anobjectisamemberofthebuiltintypeObject;andafunctionisacallableobject.Afunctionthatisassociatedwithanobjectviaapropertyiscalledamethod.

ECMAScriptdeinesacollectionofbuiltinobjectsthatroundoutthedeinitionofECMAScriptentities.Thesebuiltinobjectsincludetheglobalobject;objectsthatarefundamentaltotheruntimesemanticsofthelanguageincludingObject,Function,Boolean,Symbol,andvariousErrorobjects;objectsthatrepresentandmanipulatenumericvaluesincludingMath,Number,andDate;thetextprocessingobjectsStringandRegExp;objectsthatareindexedcollectionsofvaluesincludingArrayandninedifferentkindsofTypedArrayswhoseelementsallhaveaspeciicnumericdatarepresentation;keyedcollectionsincludingMapandSetobjects;objectssupportingstructureddataincludingtheJSONobject,ArrayBuffer,SharedArrayBuffer,andDataView;objectssupportingcontrolabstractionsincludinggeneratorfunctionsandPromiseobjects;andrelectionobjectsincludingProxyandReflect.

ECMAScriptalsodeinesasetofbuiltinoperators.ECMAScriptoperatorsincludevariousunaryoperations,multiplicativeoperators,additiveoperators,bitwiseshiftoperators,relationaloperators,equalityoperators,binarybitwiseoperators,binarylogicaloperators,assignmentoperators,andthecommaoperator.

LargeECMAScriptprogramsaresupportedbymoduleswhichallowaprogramtobedividedintomultiplesequencesofstatementsanddeclarations.Eachmoduleexplicitlyidentiiesdeclarationsitusesthatneedtobeprovidedbyothermodulesandwhichofitsdeclarationsareavailableforusebyothermodules.

ECMAScriptsyntaxintentionallyresemblesJavasyntax.ECMAScriptsyntaxisrelaxedtoenableittoserveasaneasytousescriptinglanguage.Forexample,avariableisnotrequiredtohaveitstypedeclarednoraretypesassociatedwithproperties,anddeinedfunctionsarenotrequiredtohavetheirdeclarationsappeartextuallybeforecallstothem.

EventhoughECMAScriptincludessyntaxforclassdeinitions,ECMAScriptobjectsarenotfundamentallyclassbasedsuchasthoseinC++,Smalltalk,orJava.Insteadobjectsmaybecreatedinvariouswaysincludingviaaliteralnotationorviaconstructorswhichcreateobjectsandthenexecutecodethatinitializesallorpartofthembyassigninginitialvaluestotheirproperties.Eachconstructorisafunctionthathasapropertynamed"prototype"thatisusedtoimplementprototypebasedinheritanceandsharedproperties.Objectsarecreatedbyusingconstructorsinnewexpressions;forexample,newDate(2009,11)createsanewDateobject.Invokingaconstructorwithoutusingnewhas

4.2.1 Objects

consequencesthatdependontheconstructor.Forexample,Date()producesastringrepresentationofthecurrentdateandtimeratherthananobject.

Everyobjectcreatedbyaconstructorhasanimplicitreference(calledtheobject'sprototype)tothevalueofitsconstructor's"prototype"property.Furthermore,aprototypemayhaveanonnullimplicitreferencetoitsprototype,andsoon;thisiscalledtheprototypechain.Whenareferenceismadetoapropertyinanobject,thatreferenceistothepropertyofthatnameintheirstobjectintheprototypechainthatcontainsapropertyofthatname.Inotherwords,irsttheobjectmentioneddirectlyisexaminedforsuchaproperty;ifthatobjectcontainsthenamedproperty,thatisthepropertytowhichthereferencerefers;ifthatobjectdoesnotcontainthenamedproperty,theprototypeforthatobjectisexaminednext;andsoon.

Figure1:Object/PrototypeRelationships

Inaclassbasedobjectorientedlanguage,ingeneral,stateiscarriedbyinstances,methodsarecarriedbyclasses,andinheritanceisonlyofstructureandbehaviour.InECMAScript,thestateandmethodsarecarriedbyobjects,whilestructure,behaviour,andstateareallinherited.

Allobjectsthatdonotdirectlycontainaparticularpropertythattheirprototypecontainssharethatpropertyanditsvalue.Figure1illustratesthis:

CFisaconstructor(andalsoanobject).Fiveobjectshavebeencreatedbyusingnewexpressions:cf1,cf2,cf3,cf4,andcf5.Eachoftheseobjectscontainspropertiesnamedq1andq2.Thedashedlinesrepresenttheimplicitprototyperelationship;so,forexample,cf3'sprototypeisCFp.Theconstructor,CF,hastwopropertiesitself,namedP1andP2,whicharenotvisibletoCFp,cf1,cf2,cf3,cf4,orcf5.Theproperty

PatrickStamp

namedCFP1inCFpissharedbycf1,cf2,cf3,cf4,andcf5(butnotbyCF),asareanypropertiesfoundinCFp'simplicitprototypechainthatarenotnamedq1,q2,orCFP1.NoticethatthereisnoimplicitprototypelinkbetweenCFandCFp.

Unlikemostclassbasedobjectlanguages,propertiescanbeaddedtoobjectsdynamicallybyassigningvaluestothem.Thatis,constructorsarenotrequiredtonameorassignvaluestoalloranyoftheconstructedobject'sproperties.Intheabovediagram,onecouldaddanewsharedpropertyforcf1,cf2,cf3,cf4,andcf5byassigninganewvaluetothepropertyinCFp.

AlthoughECMAScriptobjectsarenotinherentlyclassbased,itisoftenconvenienttodeineclasslikeabstractionsbaseduponacommonpatternofconstructorfunctions,prototypeobjects,andmethods.TheECMAScriptbuiltinobjectsthemselvesfollowsuchaclasslikepattern.BeginningwithECMAScript2015,theECMAScriptlanguageincludessyntacticclassdeinitionsthatpermitprogrammerstoconciselydeineobjectsthatconformtothesameclasslikeabstractionpatternusedbythebuiltinobjects.

TheECMAScriptLanguagerecognizesthepossibilitythatsomeusersofthelanguagemaywishtorestricttheirusageofsomefeaturesavailableinthelanguage.Theymightdosointheinterestsofsecurity,toavoidwhattheyconsidertobeerrorpronefeatures,togetenhancederrorchecking,orforotherreasonsoftheirchoosing.Insupportofthispossibility,ECMAScriptdeinesastrictvariantofthelanguage.ThestrictvariantofthelanguageexcludessomespeciicsyntacticandsemanticfeaturesoftheregularECMAScriptlanguageandmodiiesthedetailedsemanticsofsomefeatures.Thestrictvariantalsospeciiesadditionalerrorconditionsthatmustbereportedbythrowingerrorexceptionsinsituationsthatarenotspeciiedaserrorsbythenonstrictformofthelanguage.

ThestrictvariantofECMAScriptiscommonlyreferredtoasthestrictmodeofthelanguage.StrictmodeselectionanduseofthestrictmodesyntaxandsemanticsofECMAScriptisexplicitlymadeatthelevelofindividualECMAScriptsourcetextunits.Becausestrictmodeisselectedatthelevelofasyntacticsourcetextunit,strictmodeonlyimposesrestrictionsthathavelocaleffectwithinsuchasourcetextunit.StrictmodedoesnotrestrictormodifyanyaspectoftheECMAScriptsemanticsthatmustoperateconsistentlyacrossmultiplesourcetextunits.AcompleteECMAScriptprogrammaybecomposedofbothstrictmodeandnonstrictmodeECMAScriptsourcetextunits.Inthiscase,strictmodeonlyapplieswhenactuallyexecutingcodethatisdeinedwithinastrictmodesourcetextunit.

Inordertoconformtothisspeciication,anECMAScriptimplementationmustimplementboththefullunrestrictedECMAScriptlanguageandthestrictvariantoftheECMAScriptlanguageasdeinedbythisspeciication.Inaddition,animplementationmustsupportthecombinationofunrestrictedandstrictmodesourcetextunitsintoasinglecompositeprogram.

4.2.2 TheStrictVariantofECMAScript

4.3 TermsandDeinitions

Forthepurposesofthisdocument,thefollowingtermsanddeinitionsapply.

setofdatavaluesasdeinedinclause6ofthisspeciication

memberofoneofthetypesUndeined,Null,Boolean,Number,Symbol,orStringasdeinedinclause6

NOTE Aprimitivevalueisadatumthatisrepresenteddirectlyatthelowestlevelofthelanguageimplementation.

memberofthetypeObject

NOTE Anobjectisacollectionofpropertiesandhasasingleprototypeobject.Theprototypemaybethenullvalue.

functionobjectthatcreatesandinitializesobjects

NOTE Thevalueofaconstructor'sprototypepropertyisaprototypeobjectthatisusedtoimplementinheritanceandsharedproperties.

objectthatprovidessharedpropertiesforotherobjects

NOTE Whenaconstructorcreatesanobject,thatobjectimplicitlyreferencestheconstructor'sprototypepropertyforthepurposeofresolvingpropertyreferences.Theconstructor'sprototypepropertycanbereferencedbytheprogramexpressionconstructor.prototype,andpropertiesaddedtoanobject'sprototypeareshared,throughinheritance,byallobjectssharingtheprototype.Alternatively,anewobjectmaybecreatedwithanexplicitlyspeciiedprototypebyusingtheObject.createbuiltinfunction.

4.3 TermsandDeinitions

4.3.1 type

4.3.2 primitivevalue

4.3.3 object

4.3.4 constructor

4.3.5 prototype

4.3.6 ordinaryobject

objectthathasthedefaultbehaviourfortheessentialinternalmethodsthatmustbesupportedbyallobjects

objectthatdoesnothavethedefaultbehaviourforoneormoreoftheessentialinternalmethods

NOTE Anyobjectthatisnotanordinaryobjectisanexoticobject.

objectwhosesemanticsaredeinedbythisspeciication

objectspeciiedandsuppliedbyanECMAScriptimplementation

NOTE Standardbuiltinobjectsaredeinedinthisspeciication.AnECMAScriptimplementationmayspecifyandsupplyadditionalkindsofbuiltinobjects.Abuiltinconstructorisabuiltinobjectthatisalsoaconstructor.

primitivevalueusedwhenavariablehasnotbeenassignedavalue

typewhosesolevalueistheundeinedvalue

primitivevaluethatrepresentstheintentionalabsenceofanyobjectvalue

typewhosesolevalueisthenullvalue

4.3.6 ordinaryobject

4.3.7 exoticobject

4.3.8 standardobject

4.3.9 builtinobject

4.3.10 undeinedvalue

4.3.11 Undeinedtype

4.3.12 nullvalue

4.3.13 Nulltype

4.3.14 Booleanvalue

memberoftheBooleantype

NOTE ThereareonlytwoBooleanvalues,trueandfalse.

typeconsistingoftheprimitivevaluestrueandfalse

memberoftheObjecttypethatisaninstanceofthestandardbuiltinBooleanconstructor

NOTE ABooleanobjectiscreatedbyusingtheBooleanconstructorinanewexpression,supplyingaBooleanvalueasanargument.TheresultingobjecthasaninternalslotwhosevalueistheBooleanvalue.ABooleanobjectcanbecoercedtoaBooleanvalue.

primitivevaluethatisainiteorderedsequenceofzeroormore16bitunsignedintegervalues

NOTE AStringvalueisamemberoftheStringtype.Eachintegervalueinthesequenceusuallyrepresentsasingle16bitunitofUTF16text.However,ECMAScriptdoesnotplaceanyrestrictionsorrequirementsonthevaluesexceptthattheymustbe16bitunsignedintegers.

setofallpossibleStringvalues

memberoftheObjecttypethatisaninstanceofthestandardbuiltinStringconstructor

NOTE AStringobjectiscreatedbyusingtheStringconstructorinanewexpression,supplyin