Stage -1 Draft / April 24, 2024

Write-Once const Declarations

1 Static Semantics: Early Errors

LexicalDeclaration : LetOrConst BindingList ; LexicalBinding : BindingIdentifier Initializeropt

2 Runtime Semantics: Evaluation

LexicalDeclaration : LetOrConst BindingList ;
  1. Perform ? Evaluation of BindingList.
  2. Return empty.
 BindingList : BindingList , LexicalBinding
  1. Perform ? Evaluation of BindingList.
  2. Return ? Evaluation of LexicalBinding.
 LexicalBinding : BindingIdentifier
  1. Let lhs be ! ResolveBinding(StringValue of BindingIdentifier).
  2. Perform ! InitializeReferencedBinding(lhs, undefined).
  3. Return empty.
 Note

A static semantics rule ensures that this form of LexicalBinding never occurs in a const declaration.

 LexicalBinding : BindingIdentifier Initializer
  1. Let bindingId be StringValue of BindingIdentifier.
  2. Let lhs be ! ResolveBinding(bindingId).
  3. If IsAnonymousFunctionDefinition(Initializer) is true, then
    1. Let value be ? NamedEvaluation of Initializer with argument bindingId.
  4. Else,
    1. Let rhs be ? Evaluation of Initializer.
    2. Let value be ? GetValue(rhs).
  5. Perform ! InitializeReferencedBinding(lhs, value).
  6. Return empty.
 LexicalBinding : BindingPattern Initializer
  1. Let rhs be ? Evaluation of Initializer.
  2. Let value be ? GetValue(rhs).
  3. Let env be the running execution context's LexicalEnvironment.
  4. Return ? BindingInitialization of BindingPattern with arguments value and env.

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© 2024 Nicholas C. Zakas

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