ECMAScript® 2024 Language Specification

Draft ECMA-262 / February 15, 2024

13.3 Left-Hand-Side Expressions

Syntax

MemberExpression[Yield, Await] : PrimaryExpression[?Yield, ?Await] MemberExpression[?Yield, ?Await] [ Expression[+In, ?Yield, ?Await] ] MemberExpression[?Yield, ?Await] . IdentifierName MemberExpression[?Yield, ?Await] TemplateLiteral[?Yield, ?Await, +Tagged] SuperProperty[?Yield, ?Await] MetaProperty new MemberExpression[?Yield, ?Await] Arguments[?Yield, ?Await] MemberExpression[?Yield, ?Await] . PrivateIdentifier SuperProperty[Yield, Await] : super [ Expression[+In, ?Yield, ?Await] ] super . IdentifierName MetaProperty : NewTarget ImportMeta NewTarget : new . target ImportMeta : import . meta NewExpression[Yield, Await] : MemberExpression[?Yield, ?Await] new NewExpression[?Yield, ?Await] CallExpression[Yield, Await] : CoverCallExpressionAndAsyncArrowHead[?Yield, ?Await] SuperCall[?Yield, ?Await] ImportCall[?Yield, ?Await] CallExpression[?Yield, ?Await] Arguments[?Yield, ?Await] CallExpression[?Yield, ?Await] [ Expression[+In, ?Yield, ?Await] ] CallExpression[?Yield, ?Await] . IdentifierName CallExpression[?Yield, ?Await] TemplateLiteral[?Yield, ?Await, +Tagged] CallExpression[?Yield, ?Await] . PrivateIdentifier SuperCall[Yield, Await] : super Arguments[?Yield, ?Await] ImportCall[Yield, Await] : import ( AssignmentExpression[+In, ?Yield, ?Await] ) Arguments[Yield, Await] : ( ) ( ArgumentList[?Yield, ?Await] ) ( ArgumentList[?Yield, ?Await] , ) ArgumentList[Yield, Await] : AssignmentExpression[+In, ?Yield, ?Await] ... AssignmentExpression[+In, ?Yield, ?Await] ArgumentList[?Yield, ?Await] , AssignmentExpression[+In, ?Yield, ?Await] ArgumentList[?Yield, ?Await] , ... AssignmentExpression[+In, ?Yield, ?Await] OptionalExpression[Yield, Await] : MemberExpression[?Yield, ?Await] OptionalChain[?Yield, ?Await] CallExpression[?Yield, ?Await] OptionalChain[?Yield, ?Await] OptionalExpression[?Yield, ?Await] OptionalChain[?Yield, ?Await] OptionalChain[Yield, Await] : ?. Arguments[?Yield, ?Await] ?. [ Expression[+In, ?Yield, ?Await] ] ?. IdentifierName ?. TemplateLiteral[?Yield, ?Await, +Tagged] ?. PrivateIdentifier OptionalChain[?Yield, ?Await] Arguments[?Yield, ?Await] OptionalChain[?Yield, ?Await] [ Expression[+In, ?Yield, ?Await] ] OptionalChain[?Yield, ?Await] . IdentifierName OptionalChain[?Yield, ?Await] TemplateLiteral[?Yield, ?Await, +Tagged] OptionalChain[?Yield, ?Await] . PrivateIdentifier LeftHandSideExpression[Yield, Await] : NewExpression[?Yield, ?Await] CallExpression[?Yield, ?Await] OptionalExpression[?Yield, ?Await]

Supplemental Syntax

When processing an instance of the production
CallExpression : CoverCallExpressionAndAsyncArrowHead
the interpretation of CoverCallExpressionAndAsyncArrowHead is refined using the following grammar:

CallMemberExpression[Yield, Await] : MemberExpression[?Yield, ?Await] Arguments[?Yield, ?Await]

13.3.1 Static Semantics

13.3.1.1 Static Semantics: Early Errors

OptionalChain : ?. TemplateLiteral OptionalChain TemplateLiteral
  • It is a Syntax Error if any source text is matched by this production.
Note

This production exists in order to prevent automatic semicolon insertion rules (12.10) from being applied to the following code:

a?.b
`c`

so that it would be interpreted as two valid statements. The purpose is to maintain consistency with similar code without optional chaining:

a.b
`c`

which is a valid statement and where automatic semicolon insertion does not apply.

 ImportMeta : import . meta

13.3.2 Property Accessors

Note

Properties are accessed by name, using either the dot notation:

MemberExpression . IdentifierName
CallExpression . IdentifierName

or the bracket notation:

MemberExpression [ Expression ]
CallExpression [ Expression ]

The dot notation is explained by the following syntactic conversion:

MemberExpression . IdentifierName

is identical in its behaviour to

MemberExpression [ <identifier-name-string> ]

and similarly

CallExpression . IdentifierName

is identical in its behaviour to

CallExpression [ <identifier-name-string> ]

where <identifier-name-string> is the result of evaluating StringValue of IdentifierName.

13.3.2.1 Runtime Semantics: Evaluation

MemberExpression : MemberExpression [ Expression ]
  1. Let baseReference be ? Evaluation of MemberExpression.
  2. Let baseValue be ? GetValue(baseReference).
  3. If the source text matched by this MemberExpression is strict mode code, let strict be true; else let strict be false.
  4. Return ? EvaluatePropertyAccessWithExpressionKey(baseValue, Expression, strict).
 MemberExpression : MemberExpression . IdentifierName
  1. Let baseReference be ? Evaluation of MemberExpression.
  2. Let baseValue be ? GetValue(baseReference).
  3. If the source text matched by this MemberExpression is strict mode code, let strict be true; else let strict be false.
  4. Return EvaluatePropertyAccessWithIdentifierKey(baseValue, IdentifierName, strict).
 MemberExpression : MemberExpression . PrivateIdentifier
  1. Let baseReference be ? Evaluation of MemberExpression.
  2. Let baseValue be ? GetValue(baseReference).
  3. Let fieldNameString be the StringValue of PrivateIdentifier.
  4. Return MakePrivateReference(baseValue, fieldNameString).
 CallExpression : CallExpression [ Expression ]
  1. Let baseReference be ? Evaluation of CallExpression.
  2. Let baseValue be ? GetValue(baseReference).
  3. If the source text matched by this CallExpression is strict mode code, let strict be true; else let strict be false.
  4. Return ? EvaluatePropertyAccessWithExpressionKey(baseValue, Expression, strict).
 CallExpression : CallExpression . IdentifierName
  1. Let baseReference be ? Evaluation of CallExpression.
  2. Let baseValue be ? GetValue(baseReference).
  3. If the source text matched by this CallExpression is strict mode code, let strict be true; else let strict be false.
  4. Return EvaluatePropertyAccessWithIdentifierKey(baseValue, IdentifierName, strict).
 CallExpression : CallExpression . PrivateIdentifier
  1. Let baseReference be ? Evaluation of CallExpression.
  2. Let baseValue be ? GetValue(baseReference).
  3. Let fieldNameString be the StringValue of PrivateIdentifier.
  4. Return MakePrivateReference(baseValue, fieldNameString).

13.3.3 EvaluatePropertyAccessWithExpressionKey ( baseValue, expression, strict )

The abstract operation EvaluatePropertyAccessWithExpressionKey takes arguments baseValue (an ECMAScript language value), expression (an Expression Parse Node), and strict (a Boolean) and returns either a normal completion containing a Reference Record or an abrupt completion. It performs the following steps when called:

  1. Let propertyNameReference be ? Evaluation of expression.
  2. Let propertyNameValue be ? GetValue(propertyNameReference).
  3. Let propertyKey be ? ToPropertyKey(propertyNameValue).
  4. Return the Reference Record { [[Base]]: baseValue, [[ReferencedName]]: propertyKey, [[Strict]]: strict, [[ThisValue]]: empty }.

13.3.4 EvaluatePropertyAccessWithIdentifierKey ( baseValue, identifierName, strict )

The abstract operation EvaluatePropertyAccessWithIdentifierKey takes arguments baseValue (an ECMAScript language value), identifierName (an IdentifierName Parse Node), and strict (a Boolean) and returns a Reference Record. It performs the following steps when called:

  1. Let propertyNameString be StringValue of identifierName.
  2. Return the Reference Record { [[Base]]: baseValue, [[ReferencedName]]: propertyNameString, [[Strict]]: strict, [[ThisValue]]: empty }.

13.3.5 The new Operator

13.3.5.1 Runtime Semantics: Evaluation

NewExpression : new NewExpression
  1. Return ? EvaluateNew(NewExpression, empty).
 MemberExpression : new MemberExpression Arguments
  1. Return ? EvaluateNew(MemberExpression, Arguments).

13.3.5.1.1 EvaluateNew ( constructExpr, arguments )

The abstract operation EvaluateNew takes arguments constructExpr (a NewExpression Parse Node or a MemberExpression Parse Node) and arguments (empty or an Arguments Parse Node) and returns either a normal completion containing an ECMAScript language value or an abrupt completion. It performs the following steps when called:

  1. Let ref be ? Evaluation of constructExpr.
  2. Let constructor be ? GetValue(ref).
  3. If arguments is empty, then
    1. Let argList be a new empty List.
  4. Else,
    1. Let argList be ? ArgumentListEvaluation of arguments.
  5. If IsConstructor(constructor) is false, throw a TypeError exception.
  6. Return ? Construct(constructor, argList).

13.3.6 Function Calls

13.3.6.1 Runtime Semantics: Evaluation

CallExpression : CoverCallExpressionAndAsyncArrowHead
  1. Let expr be the CallMemberExpression that is covered by CoverCallExpressionAndAsyncArrowHead.
  2. Let memberExpr be the MemberExpression of expr.
  3. Let arguments be the Arguments of expr.
  4. Let ref be ? Evaluation of memberExpr.
  5. Let func be ? GetValue(ref).
  6. If ref is a Reference Record, IsPropertyReference(ref) is false, and ref.[[ReferencedName]] is "eval", then
    1. If SameValue(func, %eval%) is true, then
      1. Let argList be ? ArgumentListEvaluation of arguments.
      2. If argList has no elements, return undefined.
      3. Let evalArg be the first element of argList.
      4. If the source text matched by this CallExpression is strict mode code, let strictCaller be true. Otherwise let strictCaller be false.
      5. Return ? PerformEval(evalArg, strictCaller, true).
  7. Let thisCall be this CallExpression.
  8. Let tailCall be IsInTailPosition(thisCall).
  9. Return ? EvaluateCall(func, ref, arguments, tailCall).

A CallExpression evaluation that executes step 6.a.v is a direct eval.

CallExpression : CallExpression Arguments
  1. Let ref be ? Evaluation of CallExpression.
  2. Let func be ? GetValue(ref).
  3. Let thisCall be this CallExpression.
  4. Let tailCall be IsInTailPosition(thisCall).
  5. Return ? EvaluateCall(func, ref, Arguments, tailCall).

13.3.6.2 EvaluateCall ( func, ref, arguments, tailPosition )

The abstract operation EvaluateCall takes arguments func (an ECMAScript language value), ref (an ECMAScript language value or a Reference Record), arguments (a Parse Node), and tailPosition (a Boolean) and returns either a normal completion containing an ECMAScript language value or an abrupt completion. It performs the following steps when called:

  1. If ref is a Reference Record, then
    1. If IsPropertyReference(ref) is true, then
      1. Let thisValue be GetThisValue(ref).
    2. Else,
      1. Let refEnv be ref.[[Base]].
      2. Assert: refEnv is an Environment Record.
      3. Let thisValue be refEnv.WithBaseObject().
  2. Else,
    1. Let thisValue be undefined.
  3. Let argList be ? ArgumentListEvaluation of arguments.
  4. If func is not an Object, throw a TypeError exception.
  5. If IsCallable(func) is false, throw a TypeError exception.
  6. If tailPosition is true, perform PrepareForTailCall().
  7. Return ? Call(func, thisValue, argList).

13.3.7 The super Keyword

13.3.7.1 Runtime Semantics: Evaluation

SuperProperty : super [ Expression ]
  1. Let env be GetThisEnvironment().
  2. Let actualThis be ? env.GetThisBinding().
  3. Let propertyNameReference be ? Evaluation of Expression.
  4. Let propertyNameValue be ? GetValue(propertyNameReference).
  5. Let propertyKey be ? ToPropertyKey(propertyNameValue).
  6. If the source text matched by this SuperProperty is strict mode code, let strict be true; else let strict be false.
  7. Return ? MakeSuperPropertyReference(actualThis, propertyKey, strict).
 SuperProperty : super . IdentifierName
  1. Let env be GetThisEnvironment().
  2. Let actualThis be ? env.GetThisBinding().
  3. Let propertyKey be StringValue of IdentifierName.
  4. If the source text matched by this SuperProperty is strict mode code, let strict be true; else let strict be false.
  5. Return ? MakeSuperPropertyReference(actualThis, propertyKey, strict).
 SuperCall : super Arguments
  1. Let newTarget be GetNewTarget().
  2. Assert: newTarget is an Object.
  3. Let func be GetSuperConstructor().
  4. Let argList be ? ArgumentListEvaluation of Arguments.
  5. If IsConstructor(func) is false, throw a TypeError exception.
  6. Let result be ? Construct(func, argList, newTarget).
  7. Let thisER be GetThisEnvironment().
  8. Perform ? thisER.BindThisValue(result).
  9. Let F be thisER.[[FunctionObject]].
  10. Assert: F is an ECMAScript function object.
  11. Perform ? InitializeInstanceElements(result, F).
  12. Return result.

13.3.7.2 GetSuperConstructor ( )

The abstract operation GetSuperConstructor takes no arguments and returns an ECMAScript language value. It performs the following steps when called:

  1. Let envRec be GetThisEnvironment().
  2. Assert: envRec is a Function Environment Record.
  3. Let activeFunction be envRec.[[FunctionObject]].
  4. Assert: activeFunction is an ECMAScript function object.
  5. Let superConstructor be ! activeFunction.[[GetPrototypeOf]]().
  6. Return superConstructor.

13.3.7.3 MakeSuperPropertyReference ( actualThis, propertyKey, strict )

The abstract operation MakeSuperPropertyReference takes arguments actualThis (an ECMAScript language value), propertyKey (a property key), and strict (a Boolean) and returns either a normal completion containing a Super Reference Record or a throw completion. It performs the following steps when called:

  1. Let env be GetThisEnvironment().
  2. Assert: env.HasSuperBinding() is true.
  3. Let baseValue be ? env.GetSuperBase().
  4. Return the Reference Record { [[Base]]: baseValue, [[ReferencedName]]: propertyKey, [[Strict]]: strict, [[ThisValue]]: actualThis }.

13.3.8 Argument Lists

Note

The evaluation of an argument list produces a List of values.

13.3.8.1 Runtime Semantics: ArgumentListEvaluation

The syntax-directed operation ArgumentListEvaluation takes no arguments and returns either a normal completion containing a List of ECMAScript language values or an abrupt completion. It is defined piecewise over the following productions:

Arguments : ( )
  1. Return a new empty List.
 ArgumentList : AssignmentExpression
  1. Let ref be ? Evaluation of AssignmentExpression.
  2. Let arg be ? GetValue(ref).
  3. Return « arg ».
 ArgumentList : ... AssignmentExpression
  1. Let list be a new empty List.
  2. Let spreadRef be ? Evaluation of AssignmentExpression.
  3. Let spreadObj be ? GetValue(spreadRef).
  4. Let iteratorRecord be ? GetIterator(spreadObj, sync).
  5. Repeat,
    1. Let next be ? IteratorStepValue(iteratorRecord).
    2. If next is done, return list.
    3. Append next to list.
 ArgumentList : ArgumentList , AssignmentExpression
  1. Let precedingArgs be ? ArgumentListEvaluation of ArgumentList.
  2. Let ref be ? Evaluation of AssignmentExpression.
  3. Let arg be ? GetValue(ref).
  4. Return the list-concatenation of precedingArgs and « arg ».
 ArgumentList : ArgumentList , ... AssignmentExpression
  1. Let precedingArgs be ? ArgumentListEvaluation of ArgumentList.
  2. Let spreadRef be ? Evaluation of AssignmentExpression.
  3. Let iteratorRecord be ? GetIterator(? GetValue(spreadRef), sync).
  4. Repeat,
    1. Let next be ? IteratorStepValue(iteratorRecord).
    2. If next is done, return precedingArgs.
    3. Append next to precedingArgs.
 TemplateLiteral : NoSubstitutionTemplate
  1. Let templateLiteral be this TemplateLiteral.
  2. Let siteObj be GetTemplateObject(templateLiteral).
  3. Return « siteObj ».
 TemplateLiteral : SubstitutionTemplate
  1. Let templateLiteral be this TemplateLiteral.
  2. Let siteObj be GetTemplateObject(templateLiteral).
  3. Let remaining be ? ArgumentListEvaluation of SubstitutionTemplate.
  4. Return the list-concatenation of « siteObj » and remaining.
 SubstitutionTemplate : TemplateHead Expression TemplateSpans
  1. Let firstSubRef be ? Evaluation of Expression.
  2. Let firstSub be ? GetValue(firstSubRef).
  3. Let restSub be ? SubstitutionEvaluation of TemplateSpans.
  4. Assert: restSub is a possibly empty List.
  5. Return the list-concatenation of « firstSub » and restSub.

13.3.9 Optional Chains

Note
An optional chain is a chain of one or more property accesses and function calls, the first of which begins with the token ?..

13.3.9.1 Runtime Semantics: Evaluation

OptionalExpression : MemberExpression OptionalChain
  1. Let baseReference be ? Evaluation of MemberExpression.
  2. Let baseValue be ? GetValue(baseReference).
  3. If baseValue is either undefined or null, then
    1. Return undefined.
  4. Return ? ChainEvaluation of OptionalChain with arguments baseValue and baseReference.
 OptionalExpression : CallExpression OptionalChain
  1. Let baseReference be ? Evaluation of CallExpression.
  2. Let baseValue be ? GetValue(baseReference).
  3. If baseValue is either undefined or null, then
    1. Return undefined.
  4. Return ? ChainEvaluation of OptionalChain with arguments baseValue and baseReference.
 OptionalExpression : OptionalExpression OptionalChain
  1. Let baseReference be ? Evaluation of OptionalExpression.
  2. Let baseValue be ? GetValue(baseReference).
  3. If baseValue is either undefined or null, then
    1. Return undefined.
  4. Return ? ChainEvaluation of OptionalChain with arguments baseValue and baseReference.

13.3.9.2 Runtime Semantics: ChainEvaluation

The syntax-directed operation ChainEvaluation takes arguments baseValue (an ECMAScript language value) and baseReference (an ECMAScript language value or a Reference Record) and returns either a normal completion containing either an ECMAScript language value or a Reference Record, or an abrupt completion. It is defined piecewise over the following productions:

OptionalChain : ?. Arguments
  1. Let thisChain be this OptionalChain.
  2. Let tailCall be IsInTailPosition(thisChain).
  3. Return ? EvaluateCall(baseValue, baseReference, Arguments, tailCall).
 OptionalChain : ?. [ Expression ]
  1. If the source text matched by this OptionalChain is strict mode code, let strict be true; else let strict be false.
  2. Return ? EvaluatePropertyAccessWithExpressionKey(baseValue, Expression, strict).
 OptionalChain : ?. IdentifierName
  1. If the source text matched by this OptionalChain is strict mode code, let strict be true; else let strict be false.
  2. Return EvaluatePropertyAccessWithIdentifierKey(baseValue, IdentifierName, strict).
 OptionalChain : ?. PrivateIdentifier
  1. Let fieldNameString be the StringValue of PrivateIdentifier.
  2. Return MakePrivateReference(baseValue, fieldNameString).
 OptionalChain : OptionalChain Arguments
  1. Let optionalChain be OptionalChain.
  2. Let newReference be ? ChainEvaluation of optionalChain with arguments baseValue and baseReference.
  3. Let newValue be ? GetValue(newReference).
  4. Let thisChain be this OptionalChain.
  5. Let tailCall be IsInTailPosition(thisChain).
  6. Return ? EvaluateCall(newValue, newReference, Arguments, tailCall).
 OptionalChain : OptionalChain [ Expression ]
  1. Let optionalChain be OptionalChain.
  2. Let newReference be ? ChainEvaluation of optionalChain with arguments baseValue and baseReference.
  3. Let newValue be ? GetValue(newReference).
  4. If the source text matched by this OptionalChain is strict mode code, let strict be true; else let strict be false.
  5. Return ? EvaluatePropertyAccessWithExpressionKey(newValue, Expression, strict).
 OptionalChain : OptionalChain . IdentifierName
  1. Let optionalChain be OptionalChain.
  2. Let newReference be ? ChainEvaluation of optionalChain with arguments baseValue and baseReference.
  3. Let newValue be ? GetValue(newReference).
  4. If the source text matched by this OptionalChain is strict mode code, let strict be true; else let strict be false.
  5. Return EvaluatePropertyAccessWithIdentifierKey(newValue, IdentifierName, strict).
 OptionalChain : OptionalChain . PrivateIdentifier
  1. Let optionalChain be OptionalChain.
  2. Let newReference be ? ChainEvaluation of optionalChain with arguments baseValue and baseReference.
  3. Let newValue be ? GetValue(newReference).
  4. Let fieldNameString be the StringValue of PrivateIdentifier.
  5. Return MakePrivateReference(newValue, fieldNameString).

13.3.10 Import Calls

13.3.10.1 Runtime Semantics: Evaluation

ImportCall : import ( AssignmentExpression )
  1. Let referrer be GetActiveScriptOrModule().
  2. If referrer is null, set referrer to the current Realm Record.
  3. Let argRef be ? Evaluation of AssignmentExpression.
  4. Let specifier be ? GetValue(argRef).
  5. Let promiseCapability be ! NewPromiseCapability(%Promise%).
  6. Let specifierString be Completion(ToString(specifier)).
  7. IfAbruptRejectPromise(specifierString, promiseCapability).
  8. Perform HostLoadImportedModule(referrer, specifierString, empty, promiseCapability).
  9. Return promiseCapability.[[Promise]].

13.3.10.1.1 ContinueDynamicImport ( promiseCapability, moduleCompletion )

The abstract operation ContinueDynamicImport takes arguments promiseCapability (a PromiseCapability Record) and moduleCompletion (either a normal completion containing a Module Record or a throw completion) and returns unused. It completes the process of a dynamic import originally started by an import() call, resolving or rejecting the promise returned by that call as appropriate. It performs the following steps when called:

  1. If moduleCompletion is an abrupt completion, then
    1. Perform ! Call(promiseCapability.[[Reject]], undefined, « moduleCompletion.[[Value]] »).
    2. Return unused.
  2. Let module be moduleCompletion.[[Value]].
  3. Let loadPromise be module.LoadRequestedModules().
  4. Let rejectedClosure be a new Abstract Closure with parameters (reason) that captures promiseCapability and performs the following steps when called:
    1. Perform ! Call(promiseCapability.[[Reject]], undefined, « reason »).
    2. Return unused.
  5. Let onRejected be CreateBuiltinFunction(rejectedClosure, 1, "", « »).
  6. Let linkAndEvaluateClosure be a new Abstract Closure with no parameters that captures module, promiseCapability, and onRejected and performs the following steps when called:
    1. Let link be Completion(module.Link()).
    2. If link is an abrupt completion, then
      1. Perform ! Call(promiseCapability.[[Reject]], undefined, « link.[[Value]] »).
      2. Return unused.
    3. Let evaluatePromise be module.Evaluate().
    4. Let fulfilledClosure be a new Abstract Closure with no parameters that captures module and promiseCapability and performs the following steps when called:
      1. Let namespace be GetModuleNamespace(module).
      2. Perform ! Call(promiseCapability.[[Resolve]], undefined, « namespace »).
      3. Return unused.
    5. Let onFulfilled be CreateBuiltinFunction(fulfilledClosure, 0, "", « »).
    6. Perform PerformPromiseThen(evaluatePromise, onFulfilled, onRejected).
    7. Return unused.
  7. Let linkAndEvaluate be CreateBuiltinFunction(linkAndEvaluateClosure, 0, "", « »).
  8. Perform PerformPromiseThen(loadPromise, linkAndEvaluate, onRejected).
  9. Return unused.

13.3.11 Tagged Templates

Note

A tagged template is a function call where the arguments of the call are derived from a TemplateLiteral (13.2.8). The actual arguments include a template object (13.2.8.4) and the values produced by evaluating the expressions embedded within the TemplateLiteral.

13.3.11.1 Runtime Semantics: Evaluation

MemberExpression : MemberExpression TemplateLiteral
  1. Let tagRef be ? Evaluation of MemberExpression.
  2. Let tagFunc be ? GetValue(tagRef).
  3. Let thisCall be this MemberExpression.
  4. Let tailCall be IsInTailPosition(thisCall).
  5. Return ? EvaluateCall(tagFunc, tagRef, TemplateLiteral, tailCall).
 CallExpression : CallExpression TemplateLiteral
  1. Let tagRef be ? Evaluation of CallExpression.
  2. Let tagFunc be ? GetValue(tagRef).
  3. Let thisCall be this CallExpression.
  4. Let tailCall be IsInTailPosition(thisCall).
  5. Return ? EvaluateCall(tagFunc, tagRef, TemplateLiteral, tailCall).

13.3.12 Meta Properties

13.3.12.1 Runtime Semantics: Evaluation

NewTarget : new . target
  1. Return GetNewTarget().
 ImportMeta : import . meta
  1. Let module be GetActiveScriptOrModule().
  2. Assert: module is a Source Text Module Record.
  3. Let importMeta be module.[[ImportMeta]].
  4. If importMeta is empty, then
    1. Set importMeta to OrdinaryObjectCreate(null).
    2. Let importMetaValues be HostGetImportMetaProperties(module).
    3. For each Record { [[Key]], [[Value]] } p of importMetaValues, do
      1. Perform ! CreateDataPropertyOrThrow(importMeta, p.[[Key]], p.[[Value]]).
    4. Perform HostFinalizeImportMeta(importMeta, module).
    5. Set module.[[ImportMeta]] to importMeta.
    6. Return importMeta.
  5. Else,
    1. Assert: importMeta is an Object.
    2. Return importMeta.

13.3.12.1.1 HostGetImportMetaProperties ( moduleRecord )

The host-defined abstract operation HostGetImportMetaProperties takes argument moduleRecord (a Module Record) and returns a List of Records with fields [[Key]] (a property key) and [[Value]] (an ECMAScript language value). It allows hosts to provide property keys and values for the object returned from import.meta.

The default implementation of HostGetImportMetaProperties is to return a new empty List.

13.3.12.1.2 HostFinalizeImportMeta ( importMeta, moduleRecord )

The host-defined abstract operation HostFinalizeImportMeta takes arguments importMeta (an Object) and moduleRecord (a Module Record) and returns unused. It allows hosts to perform any extraordinary operations to prepare the object returned from import.meta.

Most hosts will be able to simply define HostGetImportMetaProperties, and leave HostFinalizeImportMeta with its default behaviour. However, HostFinalizeImportMeta provides an "escape hatch" for hosts which need to directly manipulate the object before it is exposed to ECMAScript code.

The default implementation of HostFinalizeImportMeta is to return unused.