ECMAScript® 2024 Language Specification

Draft ECMA-262 / July 26, 2023

8.4 Function Name Inference

8.4.1 Static Semantics: HasName

The syntax-directed operation HasName takes no arguments and returns a Boolean. It is defined piecewise over the following productions:

PrimaryExpression : CoverParenthesizedExpressionAndArrowParameterList
  1. Let expr be the ParenthesizedExpression that is covered by CoverParenthesizedExpressionAndArrowParameterList.
  2. If IsFunctionDefinition of expr is false, return false.
  3. Return HasName of expr.
 FunctionExpression : function ( FormalParameters ) { FunctionBody } GeneratorExpression : function * ( FormalParameters ) { GeneratorBody } AsyncGeneratorExpression : async function * ( FormalParameters ) { AsyncGeneratorBody } AsyncFunctionExpression : async function ( FormalParameters ) { AsyncFunctionBody } ArrowFunction : ArrowParameters => ConciseBody AsyncArrowFunction : async AsyncArrowBindingIdentifier => AsyncConciseBody CoverCallExpressionAndAsyncArrowHead => AsyncConciseBody ClassExpression : class ClassTail
  1. Return false.
 FunctionExpression : function BindingIdentifier ( FormalParameters ) { FunctionBody } GeneratorExpression : function * BindingIdentifier ( FormalParameters ) { GeneratorBody } AsyncGeneratorExpression : async function * BindingIdentifier ( FormalParameters ) { AsyncGeneratorBody } AsyncFunctionExpression : async function BindingIdentifier ( FormalParameters ) { AsyncFunctionBody } ClassExpression : class BindingIdentifier ClassTail
  1. Return true.

8.4.2 Static Semantics: IsFunctionDefinition

The syntax-directed operation IsFunctionDefinition takes no arguments and returns a Boolean. It is defined piecewise over the following productions:

PrimaryExpression : CoverParenthesizedExpressionAndArrowParameterList
  1. Let expr be the ParenthesizedExpression that is covered by CoverParenthesizedExpressionAndArrowParameterList.
  2. Return IsFunctionDefinition of expr.
 PrimaryExpression : this IdentifierReference Literal ArrayLiteral ObjectLiteral RegularExpressionLiteral TemplateLiteral MemberExpression : MemberExpression [ Expression ] MemberExpression . IdentifierName MemberExpression TemplateLiteral SuperProperty MetaProperty new MemberExpression Arguments MemberExpression . PrivateIdentifier NewExpression : new NewExpression LeftHandSideExpression : CallExpression OptionalExpression UpdateExpression : LeftHandSideExpression ++ LeftHandSideExpression -- ++ UnaryExpression -- UnaryExpression UnaryExpression : delete UnaryExpression void UnaryExpression typeof UnaryExpression + UnaryExpression - UnaryExpression ~ UnaryExpression ! UnaryExpression AwaitExpression ExponentiationExpression : UpdateExpression ** ExponentiationExpression MultiplicativeExpression : MultiplicativeExpression MultiplicativeOperator ExponentiationExpression AdditiveExpression : AdditiveExpression + MultiplicativeExpression AdditiveExpression - MultiplicativeExpression ShiftExpression : ShiftExpression << AdditiveExpression ShiftExpression >> AdditiveExpression ShiftExpression >>> AdditiveExpression RelationalExpression : RelationalExpression < ShiftExpression RelationalExpression > ShiftExpression RelationalExpression <= ShiftExpression RelationalExpression >= ShiftExpression RelationalExpression instanceof ShiftExpression RelationalExpression in ShiftExpression PrivateIdentifier in ShiftExpression EqualityExpression : EqualityExpression == RelationalExpression EqualityExpression != RelationalExpression EqualityExpression === RelationalExpression EqualityExpression !== RelationalExpression BitwiseANDExpression : BitwiseANDExpression & EqualityExpression BitwiseXORExpression : BitwiseXORExpression ^ BitwiseANDExpression BitwiseORExpression : BitwiseORExpression | BitwiseXORExpression LogicalANDExpression : LogicalANDExpression && BitwiseORExpression LogicalORExpression : LogicalORExpression || LogicalANDExpression CoalesceExpression : CoalesceExpressionHead ?? BitwiseORExpression ConditionalExpression : ShortCircuitExpression ? AssignmentExpression : AssignmentExpression AssignmentExpression : YieldExpression LeftHandSideExpression = AssignmentExpression LeftHandSideExpression AssignmentOperator AssignmentExpression LeftHandSideExpression &&= AssignmentExpression LeftHandSideExpression ||= AssignmentExpression LeftHandSideExpression ??= AssignmentExpression Expression : Expression , AssignmentExpression
  1. Return false.
 AssignmentExpression : ArrowFunction AsyncArrowFunction FunctionExpression : function BindingIdentifieropt ( FormalParameters ) { FunctionBody } GeneratorExpression : function * BindingIdentifieropt ( FormalParameters ) { GeneratorBody } AsyncGeneratorExpression : async function * BindingIdentifieropt ( FormalParameters ) { AsyncGeneratorBody } AsyncFunctionExpression : async function BindingIdentifieropt ( FormalParameters ) { AsyncFunctionBody } ClassExpression : class BindingIdentifieropt ClassTail
  1. Return true.

8.4.3 Static Semantics: IsAnonymousFunctionDefinition ( expr )

The abstract operation IsAnonymousFunctionDefinition takes argument expr (an AssignmentExpression Parse Node or an Initializer Parse Node) and returns a Boolean. It determines if its argument is a function definition that does not bind a name. It performs the following steps when called:

  1. If IsFunctionDefinition of expr is false, return false.
  2. Let hasName be HasName of expr.
  3. If hasName is true, return false.
  4. Return true.

8.4.4 Static Semantics: IsIdentifierRef

The syntax-directed operation IsIdentifierRef takes no arguments and returns a Boolean. It is defined piecewise over the following productions:

PrimaryExpression : IdentifierReference
  1. Return true.
 PrimaryExpression : this Literal ArrayLiteral ObjectLiteral FunctionExpression ClassExpression GeneratorExpression AsyncFunctionExpression AsyncGeneratorExpression RegularExpressionLiteral TemplateLiteral CoverParenthesizedExpressionAndArrowParameterList MemberExpression : MemberExpression [ Expression ] MemberExpression . IdentifierName MemberExpression TemplateLiteral SuperProperty MetaProperty new MemberExpression Arguments MemberExpression . PrivateIdentifier NewExpression : new NewExpression LeftHandSideExpression : CallExpression OptionalExpression
  1. Return false.

8.4.5 Runtime Semantics: NamedEvaluation

The syntax-directed operation NamedEvaluation takes argument name (a property key or a Private Name) and returns either a normal completion containing a function object or an abrupt completion. It is defined piecewise over the following productions:

PrimaryExpression : CoverParenthesizedExpressionAndArrowParameterList
  1. Let expr be the ParenthesizedExpression that is covered by CoverParenthesizedExpressionAndArrowParameterList.
  2. Return ? NamedEvaluation of expr with argument name.
 ParenthesizedExpression : ( Expression )
  1. Assert: IsAnonymousFunctionDefinition(Expression) is true.
  2. Return ? NamedEvaluation of Expression with argument name.
 FunctionExpression : function ( FormalParameters ) { FunctionBody }
  1. Return InstantiateOrdinaryFunctionExpression of FunctionExpression with argument name.
 GeneratorExpression : function * ( FormalParameters ) { GeneratorBody }
  1. Return InstantiateGeneratorFunctionExpression of GeneratorExpression with argument name.
 AsyncGeneratorExpression : async function * ( FormalParameters ) { AsyncGeneratorBody }
  1. Return InstantiateAsyncGeneratorFunctionExpression of AsyncGeneratorExpression with argument name.
 AsyncFunctionExpression : async function ( FormalParameters ) { AsyncFunctionBody }
  1. Return InstantiateAsyncFunctionExpression of AsyncFunctionExpression with argument name.
 ArrowFunction : ArrowParameters => ConciseBody
  1. Return InstantiateArrowFunctionExpression of ArrowFunction with argument name.
 AsyncArrowFunction : async AsyncArrowBindingIdentifier => AsyncConciseBody CoverCallExpressionAndAsyncArrowHead => AsyncConciseBody
  1. Return InstantiateAsyncArrowFunctionExpression of AsyncArrowFunction with argument name.
 ClassExpression : class ClassTail
  1. Let value be ? ClassDefinitionEvaluation of ClassTail with arguments undefined and name.
  2. Set value.[[SourceText]] to the source text matched by ClassExpression.
  3. Return value.