Stage 2 Draft / October 20, 2022

JavaScript Module Blocks

This document is a diff on top of tc39/ecma262#2905.

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 ModuleBlockExpression RegularExpressionLiteral TemplateLiteral[?Yield, ?Await, ~Tagged] CoverParenthesizedExpressionAndArrowParameterList[?Yield, ?Await]

13.2.10 Module Block Expression

Syntax

ModuleBlockExpression : module [no LineTerminator here] { ModuleBodyopt }

13.2.10.1 Runtime Semantics: Evaluation

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

13.2.10.1.1 CreateModuleBlockObject ( body, sourceText )

The abstract operation CreateModuleBlockObject takes arguments body (a String) and sourceText (a String) and returns a ModuleBlock 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 moduleBlock be OrdinaryObjectCreate(%ModuleBlock.prototype%, « [[ModuleRecord]], [[SourceText]] »).
  8. Set moduleBlock.[[ModuleRecord]] to moduleRecord.
  9. Set moduleBlock.[[SourceText]] to sourceText.
  10. Return moduleBlock.

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]].

20 Fundamental Objects

20.6 ModuleBlock Objects

20.6.1 The ModuleBlock Constructor

The ModuleBlock constructor:

  • is %ModuleBlock%.
  • is the initial value of the "ModuleBlock" 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 ModuleBlock constructor will cause an exception.

20.6.1.1 ModuleBlock ( body )

  1. Throw a TypeError exception.

20.6.1.2 ModuleBlock.prototype

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

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

20.6.2 Properties of the ModuleBlock Prototype Object

The ModuleBlock prototype object:

20.6.2.1 ModuleBlock.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

Copyright Notice

© 2022 Surma, Dan Ehrenberg, Nicolò Ribaudo

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