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spec.emu
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spec.emu
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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-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>
<emu-clause id="sec-module-namespace-exotic-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>
[[Deferred]]
</td>
<td>
a Boolean
</td>
<td>
Whether this module namespace was obtained through `import defer`/`import.defer()`. Deferred namespaces can have side effects when accessing properties on them.
</td>
</tr>
</table>
</emu-table>
<emu-clause id="sec-module-namespace-exotic-objects-get-p-receiver" type="internal method" number="8">
<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 _P_ is a Symbol, then
1. Return ! OrdinaryGet(_O_, _P_, _Receiver_).
1. <ins>If _O_.[[Deferred]] is *true*, perform ? EnsureDeferredNamespaceEvaluation(_O_).</ins>
1. Let _exports_ be _O_.[[Exports]].
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-note>
<ins>ReadyForSyncExecution can return *false* when this [[Get]] operation on a namespace coming from a deferred import is triggered during the evaluation of one of its dependencies, either synchronously or asynchronously. In that case, the module cannot be fully evaluated and some of its exports will not be initialized yet.</ins>
</emu-note>
<emu-clause id="sec-module-namespace-exotic-objects-get-p-receiver-EnsureDeferredNamespaceEvaluation" type="abstract operation">
<h1>
<ins>
EnsureDeferredNamespaceEvaluation (
_O_: a Module Namespace Exotic Object,
): either a normal completion containing ~unused~ or a throw completion
</ins>
</h1>
<dl class="header"></dl>
<emu-alg>
1. Assert: _O_.[[Deferred]] is *false*.
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 ~unused~.
</emu-alg>
</emu-clause>
<emu-clause id="sec-module-namespace-exotic-objects-get-p-receiver-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 provided, let _seen_ be 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 _required_ of _module_.[[RequestedModules]], do
1. Let _requiredModule_ be GetImportedModule(_module_, _required_.[[Specifer]]).
1. If ReadyForSyncExecution(_requiredModule_, _seen_) is *false*, then
1. Return *false*.
1. Return *true*.
</emu-alg>
</emu-clause>
</emu-clause>
<emu-clause id="sec-modulenamespacecreate" type="abstract operation" number="10">
<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. Create own properties of _M_ corresponding to the definitions in <emu-xref href="#sec-module-namespace-objects"></emu-xref>.
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>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. Return _M_.
</emu-alg>
</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] :
`import` `(` AssignmentExpression[+In, ?Yield, ?Await] `)`
<ins>`import` `.` `defer` `(` 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 intendend 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>ImportCall : `import` `(` AssignmentExpression `)`</emu-grammar>
<emu-alg>
1. <ins>Return ? EvaluateImportCall(|AssignmentExpression|, ~evaluation~).</ins>
1. <del>Let _referrer_ be GetActiveScriptOrModule().</del>
1. <del>If _referrer_ is *null*, set _referrer_ to the current Realm Record.</del>
1. <del>Let _argRef_ be ? Evaluation of |AssignmentExpression|.</del>
1. <del>Let _specifier_ be ? GetValue(_argRef_).</del>
1. <del>Let _promiseCapability_ be ! NewPromiseCapability(%Promise%).</del>
1. <del>Let _specifierString_ be Completion(ToString(_specifier_)).</del>
1. <del>IfAbruptRejectPromise(_specifierString_, _promiseCapability_).</del>
1. <del>Perform HostLoadImportedModule(_referrer_, _specifierString_, ~empty~, _promiseCapability_).</del>
1. <del>Return _promiseCapability_.[[Promise]].</del>
</emu-alg>
<emu-grammar><ins>ImportCall : `import` `.` `defer` `(` AssignmentExpression[+In, ?Yield, ?Await] `)`</ins></emu-grammar>
<emu-alg>
1. <ins>Return ? EvaluateImportCall(|AssignmentExpression|, ~defer~).</ins>
</emu-alg>
</emu-clause>
<emu-clause id="sec-evaluate-import-call" type="abstract operation">
<h1>
<ins>
EvaluateImportCall (
_specifierExpression_: a ParseNode,
_phase_: ~defer~ or ~evaluation~
): either a normal completion containing a Promise or a throw completion
</ins>
</h1>
<dl class="header"></dl>
<emu-note type="editor">
The diff presented for this algorithm is relative to the original algorithm for the Evaluation of |ImportCall| : `import` `(` |AssignmentExpression| `)`.
</emu-note>
<emu-alg>
1. Let _referrer_ be GetActiveScriptOrModule().
1. If _referrer_ is *null*, set _referrer_ to the current Realm Record.
1. Let _specifierRef_ be ? Evaluation of <del>|AssignmentExpression|</del><ins>_specifierExpression_</ins>.
1. Let _specifier_ be ? GetValue(_specifierRef_).
1. Let _promiseCapability_ be ! NewPromiseCapability(%Promise%).
1. Let _specifierString_ be Completion(ToString(_specifier_)).
1. IfAbruptRejectPromise(_specifierString_, _promiseCapability_).
1. <ins>Let _payload_ be a new DynamicImportState Record { [[PromiseCapability]]: _promiseCapability_, [[Phase]]: _phase_ }.</ins>
1. Perform HostLoadImportedModule(_referrer_, _specifierString_, ~empty~, <del>_promiseCapability_</del><ins>_payload_</ins>).
1. Return _promiseCapability_.[[Promise]].
</emu-alg>
<p><ins>A <dfn id="dynamicimportstate-record" variants="DynamicImportState Records">DynamicImportState Record</dfn> is a Record that contains information about a dynamic import call. It's used to continue loading after a call to HostLoadImportedModule. Each DynamicImportState Record has the fields defined in <emu-xref href="#table-dynamicimportstate-record-fields"></emu-xref>:</ins></p>
<emu-table id="table-dynamicimportstate-record-fields" caption="DynamicImportState Record Fields">
<table>
<tr>
<th>
Field Name
</th>
<th>
Value Type
</th>
<th>
Meaning
</th>
</tr>
<tr>
<td>
<ins>[[PromiseCapability]]</ins>
</td>
<td>
<ins>a PromiseCapability Record</ins>
</td>
<td>
<ins>The promise to resolve when the loading process finishes.</ins>
</td>
</tr>
<tr>
<td>
<ins>[[Phase]]</ins>
</td>
<td>
<ins>~defer~ or ~evaluation~</ins>
</td>
<td>
<ins>The target import phase</ins>
</td>
</tr>
</table>
</emu-table>
<emu-clause id="sec-ContinueDynamicImport" type="abstract operation">
<h1>
ContinueDynamicImport (
<del>_promiseCapability_: a PromiseCapability Record,</del>
<ins>_payload_: a DynamicImportState Record,</ins>
_moduleCompletion_: either a normal completion containing a Module Record or a throw completion,
): ~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. <ins>Let _promiseCapability_ be _payload_.[[PromiseCapability]].</ins>
1. <ins>Let _phase_ be _payload_.[[Phase]].</ins>
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. Let _evaluatePromise_ be <del>_module_.Evaluate()</del><ins>~EMPTY~</ins>.
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 a new empty List.</ins>
1. <ins>Perform GatherAsynchronousTransitiveDependencies(_module_, _evaluationList_).</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>Set _evaluatePromise_ to ! PerformPromiseAll(_iterator_, %Promise%, _pc_, %Promise.resolve%).</ins>
1. <ins>Else,</ins>
1. <ins>Assert: _phase_ is ~evaluation~.</ins>
1. <ins>Set _evaluatePromise_ to _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 up to a given phase. 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>
String
</td>
<td>
The module specifier
</td>
</tr>
<tr>
<td>
[[Phase]]
</td>
<td>
~defer~ or ~evaluation~
</td>
<td>
The target import phase
</td>
</tr>
</tbody>
</table>
</emu-table>
<emu-note type="editor">In general, this proposal replaces places where module specifiers are passed around with ModuleRequest Records. For example, several syntax-directed operations, such as ModuleRequests produce Lists of ModuleRequest Records rather than Lists of Strings which are interpreted as module specifiers. Some algorithms like ImportEntries and ImportEntriesForModule pass around ModuleRequest Records rather than Strings, in a way which doesn't require any particular textual change. Additionally, record fields in Cyclic Module Records and Source Text Module Records which contained Lists of Strings are replaced by Lists of ModuleRequest Records, as indicated above.</emu-note>
</emu-clause>
<emu-clause id="sec-static-semantics-modulerequests" type="sdo" number="3">
<h1>
Static Semantics: ModuleRequests ( ): a List of <del>Strings</del><ins>ModuleRequest Records</ins>
</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 <del>_moduleNames_</del><ins>_requests_</ins> be ModuleRequests of |ModuleItemList|.
1. Let <del>_additionalNames_</del><ins>_additionalRequests_</ins> be ModuleRequests of |ModuleItem|.
1. <del>For each String _name_ of _additionalNames_, do</del>
1. <ins>For each ModuleRequest Record _mr_ of _additionalRequests_, do</ins>
1. <ins>Let _found_ be *false*.</ins>
1. <ins>For each ModuleRequest Record _mr2_ of _requests_, do</ins>
1. <ins>If _mr_.[[Specifer]] is _mr2_.[[Specifer]] and _mr_.[[Phase]] is _mr2_.[[Phase]], then</ins>
1. <ins>Assert: _found_ is *false*.</ins>
1. <ins>Set _found_ to *true*.</ins>
1. <del>If _moduleNames_ does not contain _name_, then</del>
1. <ins>If _found_ is *false*, then</ins>
1. Append <del>_name_</del><ins>_mr_</ins> to <del>_moduleNames_</del><ins>_requests_</ins>.
1. Return <del>_moduleNames_</del><ins>_requests_</ins>.
</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. <del>Return ModuleRequests of |FromClause|.</del>
1. <ins>Let _specifier_ be SV of |FromClause|.</ins>
1. <ins>Return a List whose sole element is the ModuleRequest Record { [[Specifer]]: _specifier_, [[Phase]]: ~evaluation~ }.</ins>
</emu-alg>
<emu-grammar>
<ins>ImportDeclaration : `import` `defer` ImportClause 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 { [[Specifer]]: _specifier_, [[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. <del>Return ModuleRequests of |FromClause|.</del>
1. <ins>Let _specifier_ be SV of |FromClause|.</ins>
1. <ins>Return a List whose sole element is the ModuleRequest Record { [[Specifer]]: _specifier_, [[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">
<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-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-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>
<p>In addition to the fields defined in <emu-xref href="#table-module-record-fields"></emu-xref> Cyclic Module Records have the additional fields listed in <emu-xref href="#table-cyclic-module-fields"></emu-xref></p>
<emu-table id="table-cyclic-module-fields" caption="Additional Fields of Cyclic Module Records">
<table>
<tr>
<th>
Field Name
</th>
<th>
Value Type
</th>
<th>
Meaning
</th>
</tr>
<tr>
<td>
[[Status]]
</td>
<td>
~new~, ~unlinked~, ~linking~, ~linked~, ~evaluating~, ~evaluating-async~, or ~evaluated~
</td>
<td>
Initially ~new~. Transitions to ~unlinked~, ~linking~, ~linked~, ~evaluating~, possibly ~evaluating-async~, ~evaluated~ (in that order) as the module progresses throughout its lifecycle. ~evaluating-async~ indicates this module is queued to execute on completion of its asynchronous dependencies or it is a module whose [[HasTLA]] field is *true* that has been executed and is pending top-level completion.
</td>
</tr>
<tr>
<td>
[[EvaluationError]]
</td>
<td>
a throw completion or ~empty~
</td>
<td>
A throw completion representing the exception that occurred during evaluation. *undefined* if no exception occurred or if [[Status]] is not ~evaluated~.
</td>
</tr>
<tr>
<td>
[[DFSIndex]]
</td>
<td>
an integer or ~empty~
</td>
<td>
Auxiliary field used during Link and Evaluate only. If [[Status]] is either ~linking~ or ~evaluating~, this non-negative number records the point at which the module was first visited during the depth-first traversal of the dependency graph.
</td>
</tr>
<tr>
<td>
[[DFSAncestorIndex]]
</td>
<td>
an integer or ~empty~
</td>
<td>
Auxiliary field used during Link and Evaluate only. If [[Status]] is either ~linking~ or ~evaluating~, this is either the module's own [[DFSIndex]] or that of an "earlier" module in the same strongly connected component.
</td>
</tr>
<tr>
<td>
[[RequestedModules]]
</td>
<td>
a List of <del>Strings</del><ins>ModuleRequest Records</ins>
</td>
<td>
A List of all the |ModuleSpecifier| strings used by the module represented by this record to request the importation of a module, <ins>along with their maximum specified import phase (~defer~ or ~evaluation~)</ins>. The List is in source text occurrence order.
</td>
</tr>
<tr>
<td>
[[LoadedModules]]
</td>
<td>
a List of Records with fields [[Specifier]] (a String) and [[Module]] (a Module Record)
</td>
<td>
A map from the specifier strings used by the module represented by this record to request the importation of a module to the resolved Module Record. The list does not contain two different Records with the same [[Specifier]].
</td>
</tr>
<tr>
<td>
[[CycleRoot]]
</td>
<td>
a Cyclic Module Record or ~empty~
</td>
<td>
The first visited module of the cycle, the root DFS ancestor of the strongly connected component. For a module not in a cycle, this would be the module itself. Once Evaluate has completed, a module's [[DFSAncestorIndex]] is the [[DFSIndex]] of its [[CycleRoot]].
</td>
</tr>
<tr>
<td>
[[HasTLA]]
</td>
<td>
a Boolean
</td>
<td>
Whether this module is individually asynchronous (for example, if it's a Source Text Module Record containing a top-level await). Having an asynchronous dependency does not mean this field is *true*. This field must not change after the module is parsed.
</td>
</tr>
<tr>
<td>
[[AsyncEvaluation]]
</td>
<td>
a Boolean
</td>
<td>
Whether this module is either itself asynchronous or has an asynchronous dependency. Note: The order in which this field is set is used to order queued executions, see <emu-xref href="#sec-async-module-execution-fulfilled"></emu-xref>.
</td>
</tr>
<tr>
<td>
[[TopLevelCapability]]
</td>
<td>
a PromiseCapability Record or ~empty~
</td>
<td>
If this module is the [[CycleRoot]] of some cycle, and Evaluate() was called on some module in that cycle, this field contains the PromiseCapability Record for that entire evaluation. It is used to settle the Promise object that is returned from the Evaluate() abstract method. This field will be ~empty~ for any dependencies of that module, unless a top-level Evaluate() has been initiated for some of those dependencies.
</td>
</tr>
<tr>
<td>
[[AsyncParentModules]]
</td>
<td>
a List of Cyclic Module Records
</td>
<td>
If this module or a dependency has [[HasTLA]] *true*, and execution is in progress, this tracks the parent importers of this module for the top-level execution job. These parent modules will not start executing before this module has successfully completed execution.
</td>
</tr>
<tr>
<td>
[[PendingAsyncDependencies]]
</td>
<td>
an integer or ~empty~
</td>
<td>
If this module has any asynchronous dependencies, this tracks the number of asynchronous dependency modules remaining to execute for this module. A module with asynchronous dependencies will be executed when this field reaches 0 and there are no execution errors.
</td>
</tr>
</table>
</emu-table>
<p>In addition to the methods defined in <emu-xref href="#table-abstract-methods-of-module-records"></emu-xref> Cyclic Module Records have the additional methods listed in <emu-xref href="#table-cyclic-module-methods"></emu-xref></p>
<emu-table id="table-cyclic-module-methods" caption="Additional Abstract Methods of Cyclic Module Records">
<table>
<tr>
<th>
Method
</th>
<th>
Purpose
</th>
</tr>
<tr>
<td>
InitializeEnvironment()
</td>
<td>
Initialize the Environment Record of the module, including resolving all imported bindings, and create the module's execution context.
</td>
</tr>
<tr>
<td>
ExecuteModule( [ _promiseCapability_ ] )
</td>
<td>
Evaluate the module's code within its execution context. If this module has *true* in [[HasTLA]], then a PromiseCapability Record is passed as an argument, and the method is expected to resolve or reject the given capability. In this case, the method must not throw an exception, but instead reject the PromiseCapability Record if necessary.
</td>
</tr>
</table>
</emu-table>
<p>A <dfn id="graphloadingstate-record" variants="GraphLoadingState Records">GraphLoadingState Record</dfn> is a Record that contains information about the loading process of a module graph. It's used to continue loading after a call to HostLoadImportedModule. Each GraphLoadingState Record has the fields defined in <emu-xref href="#table-graphloadingstate-record-fields"></emu-xref>:</p>
<emu-table id="table-graphloadingstate-record-fields" caption="GraphLoadingState Record Fields">
<table>
<tr>
<th>
Field Name
</th>
<th>
Value Type
</th>
<th>
Meaning
</th>
</tr>
<tr>
<td>
[[PromiseCapability]]
</td>
<td>
a PromiseCapability Record
</td>
<td>
The promise to resolve when the loading process finishes.
</td>
</tr>
<tr>
<td>
[[IsLoading]]
</td>
<td>
a Boolean
</td>
<td>
It is true if the loading process has not finished yet, neither successfully nor with an error.
</td>
</tr>
<tr>
<td>
[[PendingModulesCount]]
</td>
<td>
a non-negative integer
</td>
<td>
It tracks the number of pending HostLoadImportedModule calls.
</td>
</tr>
<tr>
<td>
[[Visited]]
</td>
<td>
a List of Cyclic Module Records
</td>
<td>
It is a list of the Cyclic Module Records that have been already loaded by the current loading process, to avoid infinite loops with circular dependencies.
</td>
</tr>
<tr>
<td>
[[HostDefined]]
</td>
<td>
anything (default value is ~empty~)
</td>
<td>
It contains host-defined data to pass from the LoadRequestedModules caller to HostLoadImportedModule.
</td>
</tr>
</table>
</emu-table>
<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>
<dt>description</dt>
<dd>It populates the [[LoadedModules]] of all the Module Records in the dependency graph of _module_ (most of the work is done by the auxiliary function InnerModuleLoading). It takes an optional _hostDefined_ parameter that is passed to the HostLoadImportedModule hook.</dd>
</dl>
<emu-alg>
1. If _hostDefined_ is not present, let _hostDefined_ be ~empty~.
1. Let _pc_ be ! NewPromiseCapability(%Promise%).
1. Let _state_ be the GraphLoadingState Record { [[IsLoading]]: *true*, [[PendingModulesCount]]: 1, [[Visited]]: « », [[PromiseCapability]]: _pc_, [[HostDefined]]: _hostDefined_ }.
1. Perform InnerModuleLoading(_state_, _module_).
1. Return _pc_.[[Promise]].
</emu-alg>
<emu-note>
The _hostDefined_ parameter can be used to pass additional information necessary to fetch the imported modules. It is used, for example, by HTML to set the correct fetch destination for <code><link rel="preload" as="..."></code> tags.
<code>import()</code> expressions never set the _hostDefined_ parameter.
</emu-note>
<emu-clause id="sec-InnerModuleLoading" type="abstract operation">
<h1>
InnerModuleLoading (
_state_: a GraphLoadingState Record,
_module_: a Module Record,
): ~unused~
</h1>
<dl class="header">
<dt>description</dt>
<dd>It is used by LoadRequestedModules to recursively perform the actual loading process for _module_'s dependency graph.</dd>
</dl>
<emu-alg>
1. Assert: _state_.[[IsLoading]] is *true*.
1. If _module_ is a Cyclic Module Record, _module_.[[Status]] is ~new~, and _state_.[[Visited]] does not contain _module_, then
1. Append _module_ to _state_.[[Visited]].
1. Let _requestedModulesCount_ be the number of elements in _module_.[[RequestedModules]].
1. Set _state_.[[PendingModulesCount]] to _state_.[[PendingModulesCount]] + _requestedModulesCount_.
1. <del>For each String _required_ of _module_.[[RequestedModules]], do</del>
1. <ins>For each ModuleRequest Record _required_ of _module_.[[RequestedModules]], do</ins>
1. <ins>Let _specifier_ be _required_.[[Specifier]].</ins>
1. If _module_.[[LoadedModules]] contains a Record whose [[Specifier]] is <del>_required_</del><ins>_specifier_</ins>, then
1. Let _record_ be that Record.
1. Perform InnerModuleLoading(_state_, _record_.[[Module]]).
1. Else,
1. Perform HostLoadImportedModule(_module_, <del>_required_</del><ins>_specifier_</ins>, _state_.[[HostDefined]], _state_).
1. NOTE: HostLoadImportedModule will call FinishLoadingImportedModule, which re-enters the graph loading process through ContinueModuleLoading.
1. If _state_.[[IsLoading]] is *false*, return ~unused~.
1. Assert: _state_.[[PendingModulesCount]] ≥ 1.
1. Set _state_.[[PendingModulesCount]] to _state_.[[PendingModulesCount]] - 1.
1. If _state_.[[PendingModulesCount]] = 0, then
1. Set _state_.[[IsLoading]] to *false*.
1. For each Cyclic Module Record _loaded_ of _state_.[[Visited]], do
1. If _loaded_.[[Status]] is ~new~, set _loaded_.[[Status]] to ~unlinked~.
1. Perform ! Call(_state_.[[PromiseCapability]].[[Resolve]], *undefined*, « *undefined* »).
1. Return ~unused~.
</emu-alg>
</emu-clause>
<emu-clause id="sec-ContinueModuleLoading" type="abstract operation">
<h1>
ContinueModuleLoading (
_state_: a GraphLoadingState Record,
_moduleCompletion_: either a normal completion containing a Module Record or a throw completion,
): ~unused~
</h1>
<dl class="header">
<dt>description</dt>
<dd>It is used to re-enter the loading process after a call to HostLoadImportedModule.</dd>
</dl>
<emu-alg>
1. If _state_.[[IsLoading]] is *false*, return ~unused~.
1. If _moduleCompletion_ is a normal completion, then
1. Perform InnerModuleLoading(_state_, _moduleCompletion_.[[Value]]).
1. Else,
1. Set _state_.[[IsLoading]] to *false*.
1. Perform ! Call(_state_.[[PromiseCapability]].[[Reject]], *undefined*, « _moduleCompletion_.[[Value]] »).
1. Return ~unused~.
</emu-alg>
</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>
<dt>description</dt>
<dd>On success, Link transitions this module's [[Status]] from ~unlinked~ to ~linked~. On failure, an exception is thrown and this module's [[Status]] remains ~unlinked~. (Most of the work is done by the auxiliary function InnerModuleLinking.)</dd>
</dl>
<emu-alg>
1. Assert: _module_.[[Status]] is one of ~unlinked~, ~linked~, ~evaluating-async~, or ~evaluated~.
1. Let _stack_ be a new empty List.
1. Let _result_ be Completion(InnerModuleLinking(_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 ~linking~.
1. Set _m_.[[Status]] to ~unlinked~.
1. Assert: _module_.[[Status]] is ~unlinked~.
1. Return ? _result_.
1. Assert: _module_.[[Status]] is one of ~linked~, ~evaluating-async~, or ~evaluated~.
1. Assert: _stack_ is empty.
1. Return ~unused~.
</emu-alg>
<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">
<dt>description</dt>
<dd>It is used by Link to perform the actual linking process for _module_, as well as recursively on all other modules in the dependency graph. The _stack_ and _index_ parameters, as well as a module's [[DFSIndex]] and [[DFSAncestorIndex]] fields, keep track of the depth-first search (DFS) traversal. In particular, [[DFSAncestorIndex]] is used to discover strongly connected components (SCCs), such that all modules in an SCC transition to ~linked~ together.</dd>
</dl>
<emu-alg>
1. If _module_ is not a Cyclic Module Record, then
1. Perform ? _module_.Link().
1. Return _index_.
1. If _module_.[[Status]] is one of ~linking~, ~linked~, ~evaluating-async~, or ~evaluated~, then
1. Return _index_.
1. Assert: _module_.[[Status]] is ~unlinked~.
1. Set _module_.[[Status]] to ~linking~.
1. Set _module_.[[DFSIndex]] to _index_.
1. Set _module_.[[DFSAncestorIndex]] to _index_.
1. Set _index_ to _index_ + 1.
1. Append _module_ to _stack_.
1. <del>For each String _required_ of _module_.[[RequestedModules]], do</del>
1. <ins>For each ModuleRequest Record _required_ of _module_.[[RequestedModules]], do</ins>
1. Let _requiredModule_ be GetImportedModule(_module_, _required_<ins>.[[Specifier]]</ins>).
1. Set _index_ to ? InnerModuleLinking(_requiredModule_, _stack_, _index_).
1. If _requiredModule_ is a Cyclic Module Record, then
1. Assert: _requiredModule_.[[Status]] is one of ~linking~, ~linked~, ~evaluating-async~, or ~evaluated~.
1. Assert: _requiredModule_.[[Status]] is ~linking~ if and only if _stack_ contains _requiredModule_.
1. If _requiredModule_.[[Status]] is ~linking~, then
1. Set _module_.[[DFSAncestorIndex]] to min(_module_.[[DFSAncestorIndex]], _requiredModule_.[[DFSAncestorIndex]]).
1. Perform ? _module_.InitializeEnvironment().
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_.