Stage 2 Draft / December 19, 2022

Module Expressions

13 ECMAScript Language: Expressions

13.2 Primary Expression

Syntax

PrimaryExpression[Yield, Await] : this IdentifierReference[?Yield, ?Await] Literal ArrayLiteral[?Yield, ?Await] ObjectLiteral[?Yield, ?Await] FunctionExpression ClassExpression[?Yield, ?Await] GeneratorExpression AsyncFunctionExpression AsyncGeneratorExpression ModuleExpression RegularExpressionLiteral TemplateLiteral[?Yield, ?Await, ~Tagged] CoverParenthesizedExpressionAndArrowParameterList[?Yield, ?Await]

13.2.10 Module Expression

Syntax

ModuleExpression : module [no LineTerminator here] { ModuleBodyopt }

13.2.10.1 Runtime Semantics: Evaluation

ModuleExpression : module { }
  1. Let sourceText be the source text matched by ModuleExpression.
  2. Return CreateModuleObject("", sourceText).
 ModuleExpression : module { ModuleBody }
  1. Let body be the source text matched by ModuleBody.
  2. Let sourceText be the source text matched by ModuleExpression.
  3. Return CreateModuleObject(body, sourceText).

13.2.10.1.1 CreateModuleObject ( body, sourceText )

The abstract operation CreateModuleObject takes arguments body (a String) and sourceText (a String) and returns a Module Object. It performs the following steps when called:

  1. Let realm be the current Realm Record.
  2. Let hostDefined be null.
  3. Let currentScriptOrModule be GetActiveScriptOrModule().
  4. If currentScriptOrModule is not null, set hostDefined to currentScriptOrModule.[[HostDefined]].
  5. Let moduleRecord be ParseModule(body, realm, hostDefined).
  6. Assert: moduleRecord is a Module Record, because parse errors would have been reported when parsing the outer script or module.
  7. Let moduleObject be OrdinaryObjectCreate(%Module.prototype%, « [[ModuleRecord]], [[SourceText]] »).
  8. Set moduleObject.[[ModuleRecord]] to moduleRecord.
  9. Set moduleObject.[[SourceText]] to sourceText.
  10. Return moduleObject.

13.3 Left-Hand-Side Expressions

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. If Type(specifier) is Object and specifier has a [[ModuleRecord]] internal slot, then
    1. Perform ContinueDynamicImport(promiseCapability, specifier.[[ModuleRecord]]).
  7. Else,
    1. Let specifierString be Completion(ToString(specifier)).
    2. IfAbruptRejectPromise(specifierString, promiseCapability).
    3. Perform HostLoadImportedModule(referrer, specifierString, empty, promiseCapability).
  8. Return promiseCapability.[[Promise]].

14 ECMAScript Language: Statements and Declarations

14.1 Expression Statement

Syntax

ExpressionStatement[Yield, Await] : [lookahead ∉ { {, function, async [no LineTerminator here] function, class, let [, module [no LineTerminator here] { }] Expression[+In, ?Yield, ?Await] ; Note

An ExpressionStatement cannot start with a U+007B (LEFT CURLY BRACKET) because that might make it ambiguous with a Block. An ExpressionStatement cannot start with the function or class keywords because that would make it ambiguous with a FunctionDeclaration, a GeneratorDeclaration, or a ClassDeclaration. An ExpressionStatement cannot start with async function because that would make it ambiguous with an AsyncFunctionDeclaration or a AsyncGeneratorDeclaration. An ExpressionStatement cannot start with the two token sequence let [ because that would make it ambiguous with a let LexicalDeclaration whose first LexicalBinding was an ArrayBindingPattern. An ExpressionStatement cannot start with module { for forward compatibility with the Module Declarations proposal.

16 ECMAScript Language: Scripts and Modules

16.2.3 Exports

Syntax

ExportDeclaration : export ExportFromClause FromClause ; export NamedExports ; export VariableStatement[~Yield, +Await] export Declaration[~Yield, +Await] export default HoistableDeclaration[~Yield, +Await, +Default] export default ClassDeclaration[~Yield, +Await, +Default] export default [lookahead ∉ { function, async [no LineTerminator here] function, class, module [no LineTerminator here] { }] AssignmentExpression[+In, ~Yield, +Await] ; export default ModuleExpression ; Editor's Note

The export default ModuleExpression ; production is necessary for forward-compatibility with the module declarations proposal, which will replace it with export default ModuleDeclaration ;.

We cannot simply remove the ∉ { module { } lookahead in the export default AssignmentExpression ; production, because that would make the following code valid:

export default module {}.prop;

20 Fundamental Objects

20.6 Module Objects

20.6.1 The Module Constructor

The Module constructor:

  • is %Module%.
  • is the initial value of the "Module" property of the global object.
  • is not intended to be called as a function and will throw an exception when called in that manner.
  • is not intended to be used with the new operator or to be subclassed. It may be used as the value of an extends clause of a class definition but a super call to the Module constructor will cause an exception.

20.6.1.1 Module ( body )

  1. Throw a TypeError exception.

20.6.1.2 Module.prototype

The initial value of Module.prototype is the Module prototype object.

This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

20.6.2 Properties of the Module Prototype Object

The Module prototype object:

20.6.2.1 Module.prototype.toString ( )

The following steps are taken:

  1. Let module be the this value.
  2. If Type(module) is Object and has the internal slot [[ModuleRecord]], then
    1. Return module.[[SourceText]].
  3. Throw a TypeError exception.

A Copyright & Software License

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© 2022 Surma, Dan Ehrenberg, Nicolò Ribaudo

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