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<!doctype html>
<meta charset="utf8">
<link rel="stylesheet" href="./spec.css">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/8.4/styles/github.min.css">
<script src="./spec.js"></script>
<pre class="metadata">
title: Deferred Imports Evaluation
stage: 2
contributors: Nicolò Ribaudo
</pre>
<emu-note type="editor">The diff markers in this proposal are on top of <a href="https://github.com/tc39/ecma262/pull/3057">tc39/ecma262#3057</a> (Import Attributes).</emu-note>
<emu-clause id="sec-ordinary-and-exotic-objects-behaviours" number="10">
<h1>Ordinary and Exotic Objects Behaviours</h1>
<emu-clause id="sec-built-in-exotic-object-internal-methods-and-slots" number="4">
<h1>Built-in Exotic Object Internal Methods and Slots</h1>
<p>This specification defines several kinds of built-in exotic objects. These objects generally behave similar to ordinary objects except for a few specific situations. The following exotic objects use the ordinary object internal methods except where it is explicitly specified otherwise below:</p>
<!-- NOTE!!!!: the oldids here is new, don't forget it in the ecma262 PR -->
<emu-clause id="sec-module-namespace-exotic-objects" oldids="sec-module-namespace-objects" number="6">
<h1>Module Namespace Exotic Objects</h1>
<p>A module namespace exotic object is an exotic object that exposes the bindings exported from an ECMAScript |Module| (See <emu-xref href="#sec-exports"></emu-xref>). There is a one-to-one correspondence between the String-keyed own properties of a module namespace exotic object and the binding names exported by the |Module|. The exported bindings include any bindings that are indirectly exported using `export *` export items. Each String-valued own property key is the StringValue of the corresponding exported binding name. These are the only String-keyed properties of a module namespace exotic object. Each such property has the attributes { [[Writable]]: *true*, [[Enumerable]]: *true*, [[Configurable]]: *false* }. Module namespace exotic objects are not extensible.</p>
<p>An object is a <dfn id="module-namespace-exotic-object" variants="module namespace exotic objects">module namespace exotic object</dfn> if its [[GetPrototypeOf]], [[SetPrototypeOf]], [[IsExtensible]], [[PreventExtensions]], [[GetOwnProperty]], [[DefineOwnProperty]], [[HasProperty]], [[Get]], [[Set]], [[Delete]], and [[OwnPropertyKeys]] internal methods use the definitions in this section, and its other essential internal methods use the definitions found in <emu-xref href="#sec-ordinary-object-internal-methods-and-internal-slots"></emu-xref>. These methods are installed by ModuleNamespaceCreate.</p>
<p>Module namespace exotic objects have the internal slots defined in <emu-xref href="#table-internal-slots-of-module-namespace-exotic-objects"></emu-xref>.</p>
<emu-table id="table-internal-slots-of-module-namespace-exotic-objects" caption="Internal Slots of Module Namespace Exotic Objects" oldids="table-29">
<table>
<tr>
<th>
Internal Slot
</th>
<th>
Type
</th>
<th>
Description
</th>
</tr>
<tr>
<td>
[[Module]]
</td>
<td>
a Module Record
</td>
<td>
The Module Record whose exports this namespace exposes.
</td>
</tr>
<tr>
<td>
[[Exports]]
</td>
<td>
a List of Strings
</td>
<td>
A List whose elements are the String values of the exported names exposed as own properties of this object. The list is ordered as if an Array of those String values had been sorted using %Array.prototype.sort% using *undefined* as _comparefn_.
</td>
</tr>
<tr>
<td>
<ins>[[Deferred]]</ins>
</td>
<td>
<ins>a Boolean</ins>
</td>
<td>
<ins>Whether this module namespace was obtained through `import defer`/`import.defer()`. Deferred namespaces can have side effects when accessing properties on them.</ins>
</td>
</tr>
</table>
</emu-table>
<emu-clause id="sec-module-namespace-exotic-objects-getownproperty-p" type="internal method" number="5">
<h1>
[[GetOwnProperty]] (
_P_: a property key,
): either a normal completion containing either a Property Descriptor or *undefined*, or a throw completion
</h1>
<dl class="header">
<dt>for</dt>
<dd>a module namespace exotic object _O_</dd>
</dl>
<emu-alg>
1. If <del>_P_ is a Symbol</del><ins>IsSymbolLikeNamespaceKey(_P_, _O_)</ins> is *true*, return OrdinaryGetOwnProperty(_O_, _P_).
1. Let _exports_ be <del>_O_.[[Exports]]</del><ins>? GetModuleExportsList(_O_)</ins>.
1. If _exports_ does not contain _P_, return *undefined*.
1. Let _value_ be ? _O_.[[Get]](_P_, _O_).
1. Return PropertyDescriptor { [[Value]]: _value_, [[Writable]]: *true*, [[Enumerable]]: *true*, [[Configurable]]: *false* }.
</emu-alg>
</emu-clause>
<emu-clause id="sec-module-namespace-exotic-objects-defineownproperty-p-desc" type="internal method">
<h1>
[[DefineOwnProperty]] (
_P_: a property key,
_Desc_: a Property Descriptor,
): either a normal completion containing a Boolean or a throw completion
</h1>
<dl class="header">
<dt>for</dt>
<dd>a module namespace exotic object _O_</dd>
</dl>
<emu-alg>
1. If <del>_P_ is a Symbol</del><ins>IsSymbolLikeNamespaceKey(_P_, _O_)</ins>, return ! OrdinaryDefineOwnProperty(_O_, _P_, _Desc_).
1. Let _current_ be ? _O_.[[GetOwnProperty]](_P_).
1. <ins>NOTE: If _O_.[[Deferred]] is *true*, the step above will ensure that the module is evaluated.</ins>
1. If _current_ is *undefined*, return *false*.
1. If _Desc_ has a [[Configurable]] field and _Desc_.[[Configurable]] is *true*, return *false*.
1. If _Desc_ has an [[Enumerable]] field and _Desc_.[[Enumerable]] is *false*, return *false*.
1. If IsAccessorDescriptor(_Desc_) is *true*, return *false*.
1. If _Desc_ has a [[Writable]] field and _Desc_.[[Writable]] is *false*, return *false*.
1. If _Desc_ has a [[Value]] field, return SameValue(_Desc_.[[Value]], _current_.[[Value]]).
1. Return *true*.
</emu-alg>
</emu-clause>
<emu-clause id="sec-module-namespace-exotic-objects-hasproperty-p" type="internal method">
<h1>
[[HasProperty]] (
_P_: a property key,
): a normal completion containing a Boolean
</h1>
<dl class="header">
<dt>for</dt>
<dd>a module namespace exotic object _O_</dd>
</dl>
<emu-alg>
1. If <del>_P_ is a Symbol</del><ins>IsSymbolLikeNamespaceKey(_P_, _O_)</ins>, return ! OrdinaryHasProperty(_O_, _P_).
1. Let _exports_ be <del>_O_.[[Exports]]</del><ins>? GetModuleExportsList(_O_)</ins>.
1. If _exports_ contains _P_, return *true*.
1. Return *false*.
</emu-alg>
</emu-clause>
<emu-clause id="sec-module-namespace-exotic-objects-get-p-receiver" type="internal method">
<h1>
[[Get]] (
_P_: a property key,
_Receiver_: an ECMAScript language value,
): either a normal completion containing an ECMAScript language value or a throw completion
</h1>
<dl class="header">
<dt>for</dt>
<dd>a module namespace exotic object _O_</dd>
</dl>
<emu-alg>
1. If <del>_P_ is a Symbol</del><ins>IsSymbolLikeNamespaceKey(_P_, _O_)</ins>, return ! OrdinaryGet(_O_, _P_, _Receiver_).
1. Let _exports_ be <del>_O_.[[Exports]]</del><ins>? GetModuleExportsList(_O_)</ins>.
1. If _exports_ does not contain _P_, return *undefined*.
1. Let _m_ be _O_.[[Module]].
1. Let _binding_ be _m_.ResolveExport(_P_).
1. Assert: _binding_ is a ResolvedBinding Record.
1. Let _targetModule_ be _binding_.[[Module]].
1. Assert: _targetModule_ is not *undefined*.
1. If _binding_.[[BindingName]] is ~namespace~, then
1. Return GetModuleNamespace(_targetModule_, <ins>~evaluation~</ins>).
1. <ins>NOTE: The phase here is always ~evaluation~ because in `import defer * as x from "..."; export { x }`, _binding_.[[BindingName]] is *"x"* and not ~namespace~.</ins>
1. Let _targetEnv_ be _targetModule_.[[Environment]].
1. If _targetEnv_ is ~empty~, throw a *ReferenceError* exception.
1. Return ? _targetEnv_.GetBindingValue(_binding_.[[BindingName]], *true*).
</emu-alg>
<emu-note>
<p>ResolveExport is side-effect free. Each time this operation is called with a specific _exportName_, _resolveSet_ pair as arguments it must return the same result. An implementation might choose to pre-compute or cache the ResolveExport results for the [[Exports]] of each module namespace exotic object.</p>
</emu-note>
</emu-clause>
<emu-clause id="sec-module-namespace-exotic-objects-set-p-v-receiver" type="internal method">
<h1>
[[Set]] (
_P_: a property key,
_V_: an ECMAScript language value,
_Receiver_: an ECMAScript language value,
): a normal completion containing *false*
</h1>
<dl class="header">
<dt>for</dt>
<dd>a module namespace exotic object</dd>
</dl>
<emu-alg>
1. Return *false*.
</emu-alg>
</emu-clause>
<emu-clause id="sec-module-namespace-exotic-objects-delete-p" type="internal method">
<h1>
[[Delete]] (
_P_: a property key,
): a normal completion containing a Boolean
</h1>
<dl class="header">
<dt>for</dt>
<dd>a module namespace exotic object _O_</dd>
</dl>
<emu-alg>
1. If <del>_P_ is a Symbol</del><ins>IsSymbolLikeNamespaceKey(_P_, _O_)</ins>, return ! OrdinaryDelete(_O_, _P_).
1. Let _exports_ be <del>_O_.[[Exports]]</del><ins>? GetModuleExportsList(_O_)</ins>.
1. If _exports_ contains _P_, return *false*.
1. Return *true*.
</emu-alg>
</emu-clause>
<emu-clause id="sec-module-namespace-exotic-objects-ownpropertykeys" type="internal method">
<h1>[[OwnPropertyKeys]] ( ): a normal completion containing a List of property keys</h1>
<dl class="header">
<dt>for</dt>
<dd>a module namespace exotic object _O_</dd>
</dl>
<emu-alg>
1. Let _exports_ be <del>_O_.[[Exports]]</del><ins>? GetModuleExportsList(_O_)</ins>.
1. <ins>If _O_.[[Deferred]] is *true*, and _exports_ contains *"then"*, then</ins>
1. <ins>Set _exports_ to a copy of _exports_.</ins>
1. <ins>Remove *"then"* from _exports_.</ins>
1. Let _symbolKeys_ be OrdinaryOwnPropertyKeys(_O_).
1. Return the list-concatenation of _exports_ and _symbolKeys_.
</emu-alg>
</emu-clause>
<emu-clause id="sec-modulenamespacecreate" type="abstract operation">
<h1>
ModuleNamespaceCreate (
_module_: a Module Record,
_exports_: a List of Strings,
<ins>_phase_: ~defer~ or ~evaluation~,</ins>
): a module namespace exotic object
</h1>
<dl class="header">
<dt>description</dt>
<dd>It is used to specify the creation of new module namespace exotic objects.</dd>
</dl>
<emu-alg>
1. <del>Assert: _module_.[[Namespace]] is ~empty~.</del>
1. Let _internalSlotsList_ be the internal slots listed in <emu-xref href="#table-internal-slots-of-module-namespace-exotic-objects"></emu-xref>.
1. Let _M_ be MakeBasicObject(_internalSlotsList_).
1. Set _M_'s essential internal methods to the definitions specified in <emu-xref href="#sec-module-namespace-exotic-objects"></emu-xref>.
1. Set _M_.[[Module]] to _module_.
1. [declared="comparefn"] Let _sortedExports_ be a List whose elements are the elements of _exports_ ordered as if an Array of the same values had been sorted using %Array.prototype.sort% using *undefined* as _comparefn_.
1. Set _M_.[[Exports]] to _sortedExports_.
1. <del>Create own properties of _M_ corresponding to the definitions in <emu-xref href="#sec-module-namespace-objects"></emu-xref>.</del>
1. <ins>If _phase_ is ~defer~, then</ins>
1. <ins>Assert: _module_.[[DeferredNamespace]] is ~empty~.</ins>
1. <ins>Set _module_.[[DeferredNamespace]] to _M_.</ins>
1. <ins>Set _M_.[[Deferred]] to *true*.</ins>
1. <ins>Let _toStringTag_ be *"Deferred Module"*.</ins>
1. <ins>Else,</ins>
1. <ins>Assert: _module_.[[Namespace]] is ~empty~.</ins>
1. Set _module_.[[Namespace]] to _M_.
1. <ins>Set _M_.[[Deferred]] to *false*.</ins>
1. <ins>Let _toStringTag_ be *"Module"*.</ins>
1. <ins>Create an own data property of _M_ named %Symbol.toStringTag% whose [[Value]] is _toStringTag_ and whose [[Writable]], [[Enumerable]], and [[Configurable]] attributes are *false*.</ins>
1. Return _M_.
</emu-alg>
</emu-clause>
<emu-clause id="sec-IsSymbolLikeNamespaceKey" type="abstract operation">
<h1>
<ins>
IsSymbolLikeNamespaceKey (
_P_: a property key,
_ns_: a module namespace exotic object,
): a Boolean
</ins>
</h1>
<dl class="header">
<dt>description</dt>
<dd>It determines if a property of _ns_ with key _P_ would be an ordinary property, rather than being mapped to one of the module exports.</dd>
</dl>
<emu-alg>
1. If _P_ is a Symbol, return *true*.
1. If _ns_.[[Deferred]] is *true* and _P_ is *"then"*, return *true*.
1. Return *false*.
</emu-alg>
</emu-clause>
<emu-clause id="sec-GetModuleExportsList" type="abstract operation">
<h1>
<ins>
GetModuleExportsList (
_O_: a module namespace exotic object,
): either a normal completion containing a List of Strings, or a throw completion
</ins>
</h1>
<dl class="header">
<dt>description</dt>
<dd>It returns a List whose elements are the names of the module's exports, triggering module evaluation if needed.</dd>
</dl>
<emu-alg>
1. If _O_.[[Deferred]] is *true*, then
1. Let _m_ be _O_.[[Module]].
1. If _m_ is a Cyclic Module Record, _m_.[[Status]] is not ~evaluated~, and ReadyForSyncExecution(_m_) is *false*, throw a *TypeError* exception.
1. Perform ? EvaluateSync(_m_).
1. Return _O_.[[Exports]].
</emu-alg>
<emu-clause id="sec-ReadyForSyncExecution" type="abstract operation">
<h1>
<ins>
ReadyForSyncExecution (
_module_: a Cyclic Module Record,
optional _seen_: a List of Module Records,
): a Boolean
</ins>
</h1>
<dl class="header"></dl>
<emu-alg>
1. If _seen_ is not present, set _seen_ to a new empty List.
1. If _seen_ contains _module_, return *true*.
1. Append _module_ to _seen_.
1. If _module_.[[Status]] is ~evaluated~, return *true*.
1. If _module_.[[Status]] is ~evaluating~ or ~evaluating-async~, return *false*.
1. Assert: _module_.[[Status]] is ~linked~.
1. If _module_.[[HasTLA]] is *true*, return *false*.
1. For each ModuleRequest Record _request_ of _module_.[[RequestedModules]], do
1. Let _requiredModule_ be GetImportedModule(_module_, _request_).
1. If ReadyForSyncExecution(_requiredModule_, _seen_) is *false*, then
1. Return *false*.
1. Return *true*.
</emu-alg>
</emu-clause>
</emu-clause>
</emu-clause>
</emu-clause>
</emu-clause>
<emu-clause id="sec-ecmascript-language-expressions" number="13">
<h1>ECMAScript Language: Expressions</h1>
<emu-clause id="sec-left-hand-side-expressions" number="3">
<h1>Left-Hand-Side Expressions</h1>
<h2>Syntax</h2>
<emu-grammar type="definition">
ImportCall[Yield, Await] :
<del>`import` `(` AssignmentExpression[+In, ?Yield, ?Await] `,`? `)`</del>
<del>`import` `(` AssignmentExpression[+In, ?Yield, ?Await] `,` AssignmentExpression[+In, ?Yield, ?Await] `,`? `)`</del>
<ins>`import` ImportCallArguments[?Yield, ?Await]</ins>
<ins>`import` `.` `defer` ImportCallArguments[?Yield, ?Await]</ins>
<ins>
ImportCallArguments[Yield, Await] :
`(` AssignmentExpression[+In, ?Yield, ?Await] `,`? `)`
`(` AssignmentExpression[+In, ?Yield, ?Await] `,` AssignmentExpression[+In, ?Yield, ?Await] `,`? `)`
</ins>
</emu-grammar>
<emu-clause id="sec-import-calls" number="10">
<h1>Import Calls</h1>
<emu-note type="editor">
The changes to this section are intended to mirror the changes proposed by the
<a href="https://tc39.es/proposal-source-phase-imports/#sec-import-calls">Source
Phase Imports</a> proposal, but adapted to the ~defer~ phase.
</emu-note>
<emu-clause id="sec-import-call-runtime-semantics-evaluation" type="sdo">
<h1>Runtime Semantics: Evaluation</h1>
<emu-grammar><del>ImportCall : `import` `(` AssignmentExpression `,`? `)`</del></emu-grammar>
<emu-alg>
1. <del>Return ? EvaluateImportCall(|AssignmentExpression|).</del>
</emu-alg>
<emu-grammar><del>ImportCall : `import` `(` AssignmentExpression `,` AssignmentExpression `,`? `)`</del></emu-grammar>
<emu-alg>
1. <del>Return ? EvaluateImportCall(the first |AssignmentExpression|, the second |AssignmentExpression|).</del>
</emu-alg>
<emu-grammar>ImportCall : `import` ImportCallArguments</emu-grammar>
<emu-alg>
1. <ins>Return ? EvaluateImportCall(|ImportCallArguments|, ~evaluation~).</ins>
</emu-alg>
<emu-grammar>ImportCall : `import` `.` `defer` ImportCallArguments</emu-grammar>
<emu-alg>
1. <ins>Return ? EvaluateImportCall(|ImportCallArguments|, ~defer~).</ins>
</emu-alg>
</emu-clause>
<emu-clause id="sec-import-call-runtime-semantics-EvaluateImportCallSpecifier" type="sdo">
<h1><ins>Runtime Semantics: EvaluateImportCallSpecifier</ins></h1>
<emu-grammar>ImportCallArguments : `(` AssignmentExpression `,`? `)`</emu-grammar>
<emu-alg>
1. Let _ref_ be ? Evaluation of |AssignmentExpression|.
1. Return ? GetValue(_ref_).
</emu-alg>
<emu-grammar>ImportCallArguments : `(` AssignmentExpression `,` AssignmentExpression `,`? `)`</emu-grammar>
<emu-alg>
1. Let _ref_ be ? Evaluation of the first |AssignmentExpression|.
1. Return ? GetValue(_ref_).
</emu-alg>
</emu-clause>
<emu-clause id="sec-import-call-runtime-semantics-EvaluateImportCallOptions" type="sdo">
<h1><ins>Runtime Semantics: EvaluateImportCallOptions</ins></h1>
<emu-grammar>ImportCallArguments : `(` AssignmentExpression `,`? `)`</emu-grammar>
<emu-alg>
1. Return *undefined*.
</emu-alg>
<emu-grammar>ImportCallArguments : `(` AssignmentExpression `,` AssignmentExpression `,`? `)`</emu-grammar>
<emu-alg>
1. Let _ref_ be ? Evaluation of the second |AssignmentExpression|.
1. Return ? GetValue(_ref_).
</emu-alg>
</emu-clause>
<emu-clause id="sec-evaluate-import-call" type="abstract operation">
<h1>
EvaluateImportCall (
<ins>_arguments_: a Parse Node,</ins>
<ins>_phase_: ~defer~ or ~evaluation~,</ins>
<del>_specifierExpression_: a Parse Node,</del>
<del>optional _optionsExpression_: a Parse Node,</del>
): either a normal completion containing a Promise or an abrupt completion
</h1>
<dl class="header"></dl>
<emu-alg>
1. Let _referrer_ be GetActiveScriptOrModule().
1. If _referrer_ is *null*, set _referrer_ to the current Realm Record.
1. <del>Let _specifierRef_ be ? Evaluation of _specifierExpression_.</del>
1. Let _specifier_ be ? <del>GetValue(_specifierRef_)</del><ins>EvaluateImportCallSpecifier of _arguments_</ins>.
1. <del>If _optionsExpression_ is present, then</del>
1. <del>Let _optionsRef_ be ? Evaluation of _optionsExpression_.</del>
1. <del>Let _options_ be ? GetValue(_optionsRef_).</del>
1. <del>Else,</del>
1. <del>Let _options_ be *undefined*.</del>
1. <ins>Let _options_ be ? EvaluateImportCallOptions of _arguments_.</ins>
1. Let _promiseCapability_ be ! NewPromiseCapability(%Promise%).
1. Let _specifierString_ be Completion(ToString(_specifier_)).
1. IfAbruptRejectPromise(_specifierString_, _promiseCapability_).
1. Let _attributes_ be a new empty List.
1. If _options_ is not *undefined*, then
1. If _options_ is not an Object, then
1. Perform ! Call(_promiseCapability_.[[Reject]], *undefined*, « a newly created *TypeError* object »).
1. Return _promiseCapability_.[[Promise]].
1. Let _attributesObj_ be Completion(Get(_options_, *"with"*)).
1. IfAbruptRejectPromise(_attributesObj_, _promiseCapability_).
1. If _attributesObj_ is not *undefined*, then
1. If _attributesObj_ is not an Object, then
1. Perform ! Call(_promiseCapability_.[[Reject]], *undefined*, « a newly created *TypeError* object »).
1. Return _promiseCapability_.[[Promise]].
1. Let _entries_ be Completion(EnumerableOwnProperties(_attributesObj_, ~key+value~)).
1. IfAbruptRejectPromise(_entries_, _promiseCapability_).
1. For each element _entry_ of _entries_, do
1. Let _key_ be ! Get(_entry_, *"0"*).
1. Let _value_ be ! Get(_entry_, *"1"*).
1. If _key_ is a String, then
1. If _value_ is not a String, then
1. Perform ! Call(_promiseCapability_.[[Reject]], *undefined*, « a newly created *TypeError* object »).
1. Return _promiseCapability_.[[Promise]].
1. Append the ImportAttribute Record { [[Key]]: _key_, [[Value]]: _value_ } to _attributes_.
1. If AllImportAttributesSupported(_attributes_) is *false*, then
1. Perform ! Call(_promiseCapability_.[[Reject]], *undefined*, « a newly created *TypeError* object »).
1. Return _promiseCapability_.[[Promise]].
1. Sort _attributes_ according to the lexicographic order of their [[Key]] field, treating the value of each such field as a sequence of UTF-16 code unit values. NOTE: This sorting is observable only in that hosts are prohibited from changing behaviour based on the order in which attributes are enumerated.
1. Let _moduleRequest_ be a new ModuleRequest Record { [[Specifier]]: _specifierString_, [[Attributes]]: _attributes_, <ins>[[Phase]]: _phase_</ins> }.
1. Perform HostLoadImportedModule(_referrer_, _moduleRequest_, ~empty~, _promiseCapability_).
1. Return _promiseCapability_.[[Promise]].
</emu-alg>
<emu-clause id="sec-ContinueDynamicImport" type="abstract operation">
<h1>
ContinueDynamicImport (
_promiseCapability_: a PromiseCapability Record,
_moduleCompletion_: either a normal completion containing a Module Record or a throw completion,
<ins>_phase_: ~defer~ or ~evaluation~,</ins>
): ~unused~
</h1>
<dl class="header">
<dt>description</dt>
<dd>It completes the process of a dynamic import originally started by an <emu-xref href="#sec-import-calls">`import()`</emu-xref> call, resolving or rejecting the promise returned by that call as appropriate.</dd>
</dl>
<emu-alg>
1. If _moduleCompletion_ is an abrupt completion, then
1. Perform ! Call(_promiseCapability_.[[Reject]], *undefined*, « _moduleCompletion_.[[Value]] »).
1. Return ~unused~.
1. Let _module_ be _moduleCompletion_.[[Value]].
1. Let _loadPromise_ be _module_.LoadRequestedModules().
1. 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_ »).
1. Return ~unused~.
1. Let _onRejected_ be CreateBuiltinFunction(_rejectedClosure_, 1, *""*, « »).
1. Let _linkAndEvaluateClosure_ be a new Abstract Closure with no parameters that captures _module_, _promiseCapability_, <ins>_phase_</ins> and _onRejected_ and performs the following steps when called:
1. Let _link_ be Completion(_module_.Link()).
1. If _link_ is an abrupt completion, then
1. Perform ! Call(_promiseCapability_.[[Reject]], *undefined*, « _link_.[[Value]] »).
1. Return ~unused~.
1. <del>Let _evaluatePromise_ be _module_.Evaluate().</del>
1. Let _fulfilledClosure_ be a new Abstract Closure with no parameters that captures _module_, <ins>_phase_,</ins> and _promiseCapability_ and performs the following steps when called:
1. Let _namespace_ be GetModuleNamespace(_module_, <ins>_phase_</ins>).
1. Perform ! Call(_promiseCapability_.[[Resolve]], *undefined*, « _namespace_ »).
1. Return ~unused~.
1. <ins>If _phase_ is ~defer~, then</ins>
1. <ins>Let _evaluationList_ be GatherAsynchronousTransitiveDependencies(_module_).</ins>
1. <ins>If _evaluationList_ is empty, then</ins>
1. <ins>Perform _fulfilledClosure_().</ins>
1. <ins>Return ~unused~.</ins>
1. <ins>Let _asyncDepsEvaluationPromises_ be a new empty List.</ins>
1. <ins>For each Module Record _dep_ of _evaluationList_, append _dep_.Evaluate() to _asyncDepsEvaluationPromises_.</ins>
1. <ins>Let _iterator_ be CreateListIteratorRecord(_asyncDepsEvaluationPromises_).</ins>
1. <ins>Let _pc_ be ! NewPromiseCapability(%Promise%).</ins>
1. <ins>Let _evaluatePromise_ be ! PerformPromiseAll(_iterator_, %Promise%, _pc_, %Promise.resolve%).</ins>
1. <ins>Else,</ins>
1. <ins>Assert: _phase_ is ~evaluation~.</ins>
1. <ins>Let _evaluatePromise_ be _module_.Evaluate().</ins>
1. Let _onFulfilled_ be CreateBuiltinFunction(_fulfilledClosure_, *""*, 0, « »).
1. Perform PerformPromiseThen(_evaluatePromise_, _onFulfilled_, _onRejected_).
1. Return ~unused~.
1. Let _linkAndEvaluate_ be CreateBuiltinFunction(_linkAndEvaluateClosure_, *""*, 0, « »).
1. Perform PerformPromiseThen(_loadPromise_, _linkAndEvaluate_, _onRejected_).
1. Return ~unused~.
</emu-alg>
</emu-clause>
</emu-clause>
</emu-clause>
</emu-clause>
</emu-clause>
<emu-clause id="sec-ecmascript-language-scripts-and-modules" number="16">
<h1>ECMAScript Language: Scripts and Modules</h1>
<emu-clause id="sec-modules" number="2">
<h1>Modules</h1>
<h2>Syntax</h2>
<emu-grammar type="definition">
Module :
ModuleBody?
ModuleBody :
ModuleItemList
ModuleItemList :
ModuleItem
ModuleItemList ModuleItem
ModuleItem :
ImportDeclaration
ExportDeclaration
StatementListItem[~Yield, +Await, ~Return]
ModuleExportName :
IdentifierName
StringLiteral
</emu-grammar>
<emu-clause id="sec-module-semantics">
<h1>Module Semantics</h1>
<emu-clause id="sec-modulerequest-record">
<h1><ins>ModuleRequest Records</ins></h1>
<p>A <dfn id="modulerequest-record" variants="ModuleRequest Records">ModuleRequest Record</dfn> represents the request to import a module with given import attributes <ins>and import phase</ins>. It consists of the following fields:</p>
<emu-table id="table-modulerequest-fields" caption="ModuleRequest Record Fields">
<table>
<tbody>
<tr>
<th>
Field Name
</th>
<th>
Value Type
</th>
<th>
Meaning
</th>
</tr>
<tr>
<td>
[[Specifier]]
</td>
<td>
a String
</td>
<td>
The module specifier
</td>
</tr>
<tr>
<td>
[[Attributes]]
</td>
<td>
a List of ImportAttribute Records
</td>
<td>
The import attributes
</td>
</tr>
<tr>
<td>
<ins>[[Phase]]</ins>
</td>
<td>
<ins>~defer~ or ~evaluation~</ins>
</td>
<td>
<ins>The target import phase</ins>
</td>
</tr>
</tbody>
</table>
</emu-table>
<emu-clause id="sec-ModuleRequestsEqual" type="abstract operation">
<h1>
ModuleRequestsEqual (
_left_: a ModuleRequest Record or a LoadedModuleRequest Record,
_right_: a ModuleRequest Record or a LoadedModuleRequest Record,
): a Boolean
</h1>
<dl class="header">
<dt>description</dt>
<dd>‍<ins>It checks whether the two ModuleRequest Records have the same specifier and attributes.</ins></dd>
</dl>
<emu-alg>
1. If _left_.[[Specifier]] is not _right_.[[Specifier]], return *false*.
1. Let _leftAttrs_ be _left_.[[Attributes]].
1. Let _rightAttrs_ be _right_.[[Attributes]].
1. Let _leftAttrsCount_ be the number of elements in _leftAttrs_.
1. Let _rightAttrsCount_ be the number of elements in _rightAttrs_.
1. If _leftAttrsCount_ ≠ _rightAttrsCount_, return *false*.
1. For each ImportAttribute Record _l_ of _leftAttrs_, do
1. If _rightAttrs_ does not contain an ImportAttribute Record _r_ such that _l_.[[Key]] is _r_.[[Key]] and _l_.[[Value]] is _r_.[[Value]], return *false*.
1. Return *true*.
</emu-alg>
</emu-clause>
</emu-clause>
<emu-clause id="sec-static-semantics-modulerequests" type="sdo" number="3">
<h1>Static Semantics: ModuleRequests ( ): a List of ModuleRequest Records</h1>
<dl class="header">
</dl>
<emu-grammar>Module : [empty]</emu-grammar>
<emu-alg>
1. Return a new empty List.
</emu-alg>
<emu-grammar>ModuleItemList : ModuleItem</emu-grammar>
<emu-alg>
1. Return ModuleRequests of |ModuleItem|.
</emu-alg>
<emu-grammar>ModuleItemList : ModuleItemList ModuleItem</emu-grammar>
<emu-alg>
1. Let _requests_ be the ModuleRequests of |ModuleItemList|.
1. Let _additionalRequests_ be the ModuleRequests of |ModuleItem|.
1. For each ModuleRequest Record _mr_ of _additionalRequests_, do
1. If _requests_ does not contain a ModuleRequest Record _mr2_ such that ModuleRequestsEqual(_mr_, _mr2_) is *true* <ins>and _mr_.[[Phase]] is _mr2_.[[Phase]]</ins>, then
1. Append _mr_ to _requests_.
1. Return _requests_.
</emu-alg>
<emu-grammar>ModuleItem : StatementListItem</emu-grammar>
<emu-alg>
1. Return a new empty List.
</emu-alg>
<emu-grammar>
ImportDeclaration : `import` ImportClause FromClause `;`
</emu-grammar>
<emu-alg>
1. Let _specifier_ be the SV of |FromClause|.
1. Return a List whose sole element is the ModuleRequest Record { [[Specifier]]: _specifier_, [[Attributes]]: « », <ins>[[Phase]]: ~evaluation~</ins> }.
</emu-alg>
<emu-grammar>ImportDeclaration : `import` ImportClause FromClause WithClause `;`</emu-grammar>
<emu-alg>
1. Let _specifier_ be the SV of |FromClause|.
1. Let _attributes_ be WithClauseToAttributes of |WithClause|.
1. Return a List whose sole element is the ModuleRequest Record { [[Specifier]]: _specifier_, [[Attributes]]: _attributes_, <ins>[[Phase]]: ~evaluation~</ins> }.
</emu-alg>
<emu-grammar>
<ins>ImportDeclaration : `import` `defer` NameSpaceImport FromClause `;`</ins>
</emu-grammar>
<emu-alg>
1. <ins>Let _specifier_ be SV of |FromClause|.</ins>
1. <ins>Return a List whose sole element is the ModuleRequest Record { [[Specifier]]: _specifier_, [[Attributes]]: « », [[Phase]]: ~defer~ }.</ins>
</emu-alg>
<emu-grammar>
<ins>ImportDeclaration : `import` `defer` NameSpaceImport FromClause WithClause `;`</ins>
</emu-grammar>
<emu-alg>
1. <ins>Let _specifier_ be SV of |FromClause|.</ins>
1. <ins>Let _attributes_ be WithClauseToAttributes of |WithClause|.</ins>
1. <ins>Return a List whose sole element is the ModuleRequest Record { [[Specifier]]: _specifier_, [[Attributes]]: _attributes_, [[Phase]]: ~defer~ }.</ins>
</emu-alg>
<emu-grammar><del>ModuleSpecifier : StringLiteral</del></emu-grammar>
<emu-alg>
1. <del>Return a List whose sole element is the SV of |StringLiteral|.</del>
</emu-alg>
<emu-grammar>
ExportDeclaration : `export` ExportFromClause FromClause `;`
</emu-grammar>
<emu-alg>
1. Let _specifier_ be SV of |FromClause|.
1. Return a List whose sole element is the ModuleRequest Record { [[Specifier]]: _specifier_, [[Attributes]]: « », <ins>[[Phase]]: ~evaluation~</ins> }.
</emu-alg>
<emu-grammar>
ExportDeclaration : `export` ExportFromClause FromClause WithClause `;`
</emu-grammar>
<emu-alg>
1. Let _specifier_ be the SV of |FromClause|.
1. Let _attributes_ be WithClauseToAttributes of |WithClause|.
1. Return a List whose sole element is the ModuleRequest Record { [[Specifier]]: _specifier_, [[Attributes]]: _attributes_, <ins>[[Phase]]: ~evaluation~</ins> }.
</emu-alg>
<emu-grammar>
ExportDeclaration :
`export` NamedExports `;`
`export` VariableStatement
`export` Declaration
`export` `default` HoistableDeclaration
`export` `default` ClassDeclaration
`export` `default` AssignmentExpression `;`
</emu-grammar>
<emu-alg>
1. Return a new empty List.
</emu-alg>
</emu-clause>
<emu-clause id="sec-abstract-module-records" number="4">
<h1>Abstract Module Records</h1>
<p>A <dfn variants="Module Records">Module Record</dfn> encapsulates structural information about the imports and exports of a single module. This information is used to link the imports and exports of sets of connected modules. A Module Record includes four fields that are only used when evaluating a module.</p>
<p>For specification purposes Module Record values are values of the Record specification type and can be thought of as existing in a simple object-oriented hierarchy where Module Record is an abstract class with both abstract and concrete subclasses. This specification defines the abstract subclass named Cyclic Module Record and its concrete subclass named Source Text Module Record. Other specifications and implementations may define additional Module Record subclasses corresponding to alternative module definition facilities that they defined.</p>
<p>Module Record defines the fields listed in <emu-xref href="#table-module-record-fields"></emu-xref>. All Module Definition subclasses include at least those fields. Module Record also defines the abstract method list in <emu-xref href="#table-abstract-methods-of-module-records"></emu-xref>. All Module definition subclasses must provide concrete implementations of these abstract methods.</p>
<emu-table id="table-module-record-fields" caption="Module Record Fields" oldids="table-36">
<table>
<thead>
<tr>
<th>
Field Name
</th>
<th>
Value Type
</th>
<th>
Meaning
</th>
</tr>
</thead>
<tr>
<td>
[[Realm]]
</td>
<td>
a Realm Record
</td>
<td>
The Realm within which this module was created.
</td>
</tr>
<tr>
<td>
[[Environment]]
</td>
<td>
a Module Environment Record or ~empty~
</td>
<td>
The Environment Record containing the top level bindings for this module. This field is set when the module is linked.
</td>
</tr>
<tr>
<td>
[[Namespace]]
</td>
<td>
an Object or ~empty~
</td>
<td>
The Module Namespace Object (<emu-xref href="#sec-module-namespace-exotic-objects"></emu-xref>) whose [[Deferred]] slot is *false*, if one has been created for this module.
</td>
</tr>
<tr>
<td>
<ins>[[DeferredNamespace]]</ins>
</td>
<td>
<ins>an Object or ~empty~</ins>
</td>
<td>
<ins>The Module Namespace Object (<emu-xref href="#sec-module-namespace-exotic-objects"></emu-xref>) whose [[Deferred]] slot is *true*, if one has been requested for this module.</ins>
</td>
</tr>
<tr>
<td>
[[HostDefined]]
</td>
<td>
anything (default value is *undefined*)
</td>
<td>
Field reserved for use by host environments that need to associate additional information with a module.
</td>
</tr>
</table>
</emu-table>
</emu-clause>
<emu-clause id="sec-cyclic-module-records" number="5">
<h1>Cyclic Module Records</h1>
<p>A <dfn id="cyclic-module-record" variants="Cyclic Module Records">Cyclic Module Record</dfn> is used to represent information about a module that can participate in dependency cycles with other modules that are subclasses of the Cyclic Module Record type. Module Records that are not subclasses of the Cyclic Module Record type must not participate in dependency cycles with Source Text Module Records.</p>
<emu-clause id="sec-LoadRequestedModules" type="concrete method">
<h1>
LoadRequestedModules (
optional _hostDefined_: anything,
): a Promise
</h1>
<dl class="header">
<dt>for</dt>
<dd>a Cyclic Module Record _module_</dd>
</dl>
<emu-clause id="sec-InnerModuleLoading" type="abstract operation">
<h1>
InnerModuleLoading (
_state_: a GraphLoadingState Record,
_module_: a Module Record,
): ~unused~
</h1>
<dl class="header">
</dl>
<emu-note>
<ins>There is no special handling for ModuleRequests whose [[Phase]] is ~defer~: any error from loading or parsing the corresponding modules will make InnerModuleLoading fail.</ins>
</emu-note>
</emu-clause>
</emu-clause>
<emu-clause id="sec-moduledeclarationlinking" type="concrete method" oldids="sec-moduledeclarationinstantiation">
<h1>Link ( ): either a normal completion containing ~unused~ or a throw completion</h1>
<dl class="header">
<dt>for</dt>
<dd>a Cyclic Module Record _module_</dd>
</dl>
<emu-clause id="sec-InnerModuleLinking" type="abstract operation" oldids="sec-innermoduleinstantiation">
<h1>
InnerModuleLinking (
_module_: a Module Record,
_stack_: a List of Cyclic Module Records,
_index_: a non-negative integer,
): either a normal completion containing a non-negative integer or a throw completion
</h1>
<dl class="header">
</dl>
<emu-note>
<ins>There is no special handling for ModuleRequests whose [[Phase]] is ~defer~: any error from linking the corresponding modules will make InnerModuleLinking fail.</ins>
</emu-note>
</emu-clause>
</emu-clause>
<emu-clause id="sec-moduleevaluation" type="concrete method">
<h1>Evaluate ( ): a Promise</h1>
<dl class="header">
<dt>for</dt>
<dd>a Cyclic Module Record _module_</dd>
<dt>description</dt>
<dd>Evaluate transitions this module's [[Status]] from ~linked~ to either ~evaluating-async~ or ~evaluated~. The first time it is called on a module in a given strongly connected component, Evaluate creates and returns a Promise which resolves when the module has finished evaluating. This Promise is stored in the [[TopLevelCapability]] field of the [[CycleRoot]] for the component. Future invocations of Evaluate on any module in the component return the same Promise. (Most of the work is done by the auxiliary function InnerModuleEvaluation.)</dd>
</dl>
<emu-alg>
1. <del>Assert: This call to Evaluate is not happening at the same time as another call to Evaluate within the surrounding agent.</del>.
1. <ins>Assert: None of _module_ or any of its recursive dependencies have [[Status]] set to ~evaluating~, ~linking~, ~unlinked~, or ~new~.</ins>
1. Assert: _module_.[[Status]] is one of ~linked~, ~evaluating-async~, or ~evaluated~.
1. If _module_.[[Status]] is either ~evaluating-async~ or ~evaluated~, set _module_ to _module_.[[CycleRoot]].
1. If _module_.[[TopLevelCapability]] is not ~empty~, then
1. Return _module_.[[TopLevelCapability]].[[Promise]].
1. Let _stack_ be a new empty List.
1. Let _capability_ be ! NewPromiseCapability(%Promise%).
1. Set _module_.[[TopLevelCapability]] to _capability_.
1. Let _result_ be Completion(InnerModuleEvaluation(_module_, _stack_, 0)).
1. If _result_ is an abrupt completion, then
1. For each Cyclic Module Record _m_ of _stack_, do
1. Assert: _m_.[[Status]] is ~evaluating~.
1. Set _m_.[[Status]] to ~evaluated~.
1. Set _m_.[[EvaluationError]] to _result_.
1. Assert: _module_.[[Status]] is ~evaluated~.
1. Assert: _module_.[[EvaluationError]] is _result_.
1. Perform ! Call(_capability_.[[Reject]], *undefined*, « _result_.[[Value]] »).
1. Else,
1. Assert: _module_.[[Status]] is either ~evaluating-async~ or ~evaluated~.
1. Assert: _module_.[[EvaluationError]] is ~empty~.
1. If _module_.[[AsyncEvaluation]] is *false*, then
1. Assert: _module_.[[Status]] is ~evaluated~.
1. Perform ! Call(_capability_.[[Resolve]], *undefined*, « *undefined* »).
1. Assert: _stack_ is empty.
1. Return _capability_.[[Promise]].
</emu-alg>
<emu-clause id="sec-innermoduleevaluation" type="abstract operation">
<h1>
InnerModuleEvaluation (
_module_: a Module Record,
_stack_: a List of Cyclic Module Records,
_index_: a non-negative integer,
): either a normal completion containing a non-negative integer or a throw completion
</h1>
<dl class="header">
<dt>description</dt>
<dd>It is used by Evaluate to perform the actual evaluation process for _module_, as well as recursively on all other modules in the dependency graph. The _stack_ and _index_ parameters, as well as _module_'s [[DFSIndex]] and [[DFSAncestorIndex]] fields, are used the same way as in InnerModuleLinking.</dd>
</dl>
<emu-alg>
1. If _module_ is not a Cyclic Module Record, then
1. <del>Let _promise_ be ! _module_.Evaluate().</del>
1. <del>Assert: _promise_.[[PromiseState]] is not ~pending~.</del>
1. <del>If _promise_.[[PromiseState]] is ~rejected~, then</del>
1. <del>Return ThrowCompletion(_promise_.[[PromiseResult]]).</del>
1. <ins>Perform ? EvaluateSync(_module_).</ins>
1. Return _index_.
1. If _module_.[[Status]] is either ~evaluating-async~ or ~evaluated~, then
1. If _module_.[[EvaluationError]] is ~empty~, return _index_.
1. Otherwise, return ? _module_.[[EvaluationError]].
1. If _module_.[[Status]] is ~evaluating~, return _index_.
1. Assert: _module_.[[Status]] is ~linked~.
1. Set _module_.[[Status]] to ~evaluating~.
1. Set _module_.[[DFSIndex]] to _index_.
1. Set _module_.[[DFSAncestorIndex]] to _index_.
1. Set _module_.[[PendingAsyncDependencies]] to 0.
1. Set _index_ to _index_ + 1.
1. <ins>Let _evaluationList_ be a new empty List.</ins>
1. <ins>For each ModuleRequest Record _request_ of _module_.[[RequestedModules]], do</ins>
1. <ins>Let _requiredModule_ be GetImportedModule(_module_, _request_).</ins>
1. <ins>If _request_.[[Phase]] is ~defer~, then</ins>
1. <ins>Let _additionalModules_ be GatherAsynchronousTransitiveDependencies(_requiredModule_).</ins>
1. <ins>For each Module Record _additionalModule_ of _additionalModules_, do</ins>
1. <ins>If _evaluationList_ does not contain _additionalModule_, then</ins>
1. <ins>Append _additionalModule_ to _evaluationList_.</ins>
1. <ins>Else if _evaluationList_ does not contain _requiredModule_, then</ins>
1. <ins>Append _requiredModule_ to _evaluationList_.</ins>
1. Append _module_ to _stack_.
1. <del>For each ModuleRequest Record _request_ of _module_.[[RequestedModules]], do</del>
1. <del>Let _requiredModule_ be GetImportedModule(_module_, _request_).</del>
1. <ins>For each Module Record _requiredModule_ of _evaluationList_, do</ins>
1. Set _index_ to ? InnerModuleEvaluation(_requiredModule_, _stack_, _index_).
1. If _requiredModule_ is a Cyclic Module Record, then
1. Assert: _requiredModule_.[[Status]] is one of ~evaluating~, ~evaluating-async~, or ~evaluated~.
1. Assert: _requiredModule_.[[Status]] is ~evaluating~ if and only if _stack_ contains _requiredModule_.
1. If _requiredModule_.[[Status]] is ~evaluating~, then
1. Set _module_.[[DFSAncestorIndex]] to min(_module_.[[DFSAncestorIndex]], _requiredModule_.[[DFSAncestorIndex]]).
1. Else,
1. Set _requiredModule_ to _requiredModule_.[[CycleRoot]].
1. Assert: _requiredModule_.[[Status]] is either ~evaluating-async~ or ~evaluated~.
1. If _requiredModule_.[[EvaluationError]] is not ~empty~, return ? _requiredModule_.[[EvaluationError]].
1. If _requiredModule_.[[AsyncEvaluation]] is *true*, then
1. Set _module_.[[PendingAsyncDependencies]] to _module_.[[PendingAsyncDependencies]] + 1.
1. Append _module_ to _requiredModule_.[[AsyncParentModules]].
1. If _module_.[[PendingAsyncDependencies]] > 0 or _module_.[[HasTLA]] is *true*, then
1. Assert: _module_.[[AsyncEvaluation]] is *false*.
1. Set _module_.[[AsyncEvaluation]] to *true*.
1. NOTE: The order in which module records have their [[AsyncEvaluation]] fields transition to *true* is significant. (See <emu-xref href="#sec-async-module-execution-fulfilled"></emu-xref>.)
1. If _module_.[[PendingAsyncDependencies]] = 0, perform ExecuteAsyncModule(_module_).
1. Else,
1. Perform ? <emu-meta effects="user-code">_module_.ExecuteModule()</emu-meta>.
1. Assert: _module_ occurs exactly once in _stack_.
1. Assert: _module_.[[DFSAncestorIndex]] ≤ _module_.[[DFSIndex]].
1. If _module_.[[DFSAncestorIndex]] = _module_.[[DFSIndex]], then
1. Let _done_ be *false*.
1. Repeat, while _done_ is *false*,
1. Let _requiredModule_ be the last element of _stack_.
1. Remove the last element of _stack_.
1. Assert: _requiredModule_ is a Cyclic Module Record.
1. If _requiredModule_.[[AsyncEvaluation]] is *false*, then
1. Set _requiredModule_.[[Status]] to ~evaluated~.
1. Else,
1. Set _requiredModule_.[[Status]] to ~evaluating-async~.
1. If _requiredModule_ and _module_ are the same Module Record, set _done_ to *true*.
1. Set _requiredModule_.[[CycleRoot]] to _module_.
1. Return _index_.
</emu-alg>
<emu-note>
<p>A module is ~evaluating~ while it is being traversed by InnerModuleEvaluation. A module is ~evaluated~ on execution completion or ~evaluating-async~ during execution if its [[HasTLA]] field is *true* or if it has asynchronous dependencies.</p>
</emu-note>
<emu-note>
<p>Any modules depending on a module of an asynchronous cycle when that cycle is not ~evaluating~ will instead depend on the execution of the root of the cycle via [[CycleRoot]]. This ensures that the cycle state can be treated as a single strongly connected component through its root module state.</p>
</emu-note>
</emu-clause>
<emu-clause id="sec-EvaluateSync" type="abstract operation">
<h1>
<ins>
EvaluateSync (
_module_: a Module Record,
): either a normal completion containing ~unused~ or a throw completion
</ins>
</h1>
<dl class="header">
<dt>description</dt>
<dd>It synchronously evaluates _module_ provided it is ready for synchronous execution.</dd>
</dl>
<emu-alg>
1. Assert: If _module_ is a Cyclic Module Record, _module_.[[HasTLA]] is *false*.
1. [declared="m"] Assert: For each Cyclic Module Record _m_ that it a transitive dependency of _module_, either _m_.[[HasTLA]] is *false* or _m_.[[Status]] is ~evaluated~.
1. Let _promise_ be ! _module_.Evaluate().