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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="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/8.4/styles/github.min.css">
<link rel="spec" href="es2015" />
<style>
h1.ins {
background-color: #e0f8e0;
text-decoration: none;
border-bottom: 1px solid #396;
}
hr {
height: 0.25em;
background: #ccc;
border: 0;
margin: 2em 0;
}
.unicode-property-table {
table-layout: fixed;
width: 100%;
font-size: 80%;
}
.unicode-property-table ul {
padding-left: 0;
list-style: none;
}
</style>
<pre class="metadata">
title: ECMAScript Explicit Resource Management
status: proposal
stage: 3
contributors: Ron Buckton, Ecma International
</pre>
<emu-biblio href="node_modules/@tc39/ecma262-biblio/biblio.json"></emu-biblio>
<emu-intro id="intro">
<h1>Introduction</h1>
<p>This proposal introduces syntax and semantics around explicit resource management.</p>
<p>See <a href="https://github.com/tc39/proposal-explicit-resource-management">the proposal repository</a> for background material and discussion.</p>
</emu-intro>
<emu-clause id="sec-ecmascript-data-types-and-values" aoid="Type">
<h1>ECMAScript Data Types and Values</h1>
<emu-clause id="sec-ecmascript-language-types">
<h1>ECMAScript Language Types</h1>
<emu-clause id="sec-ecmascript-language-types-symbol-type">
<h1>The Symbol Type</h1>
<emu-clause id="sec-well-known-symbols">
<h1>Well-Known Symbols</h1>
<emu-table id="table-1" caption="Well-known Symbols">
<table>
<tbody>
<tr>
<th>
Specification Name
</th>
<th>
[[Description]]
</th>
<th>
Value and Purpose
</th>
</tr>
<tr>
<td>
<ins>@@asyncDispose</ins>
</td>
<td>
<ins>`"Symbol.asyncDispose"`</ins>
</td>
<td>
<ins>A method that performs explicit resource cleanup on an object. Called by the semantics of the `await using` declaration and AsyncDisposableStack objects.</ins>
</td>
</tr>
<tr>
<td>
<ins>@@dispose</ins>
</td>
<td>
<ins>`"Symbol.dispose"`</ins>
</td>
<td>
<ins>A method that performs explicit resource cleanup on an object. Called by the semantics of the `using` declaration and DisposableStack objects.</ins>
</td>
</tr>
</tbody>
</table>
</emu-table>
</emu-clause>
</emu-clause>
<emu-clause id="sec-object-type">
<h1>The Object Type</h1>
<emu-clause id="sec-well-known-intrinsic-objects">
<h1>Well-Known Intrinsic Objects</h1>
<emu-table id="table-well-known-intrinsic-objects" caption="Well-Known Intrinsic Objects" oldids="table-7">
<table>
<tr>
<th>
Intrinsic Name
</th>
<th>
Global Name
</th>
<th>
ECMAScript Language Association
</th>
</tr>
<tr>
<td>
%AggregateError%
</td>
<td>
`AggregateError`
</td>
<td>
The `AggregateError` constructor (<emu-xref href="#sec-aggregate-error-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Array%
</td>
<td>
`Array`
</td>
<td>
The Array constructor (<emu-xref href="#sec-array-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%ArrayBuffer%
</td>
<td>
`ArrayBuffer`
</td>
<td>
The ArrayBuffer constructor (<emu-xref href="#sec-arraybuffer-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%ArrayIteratorPrototype%
</td>
<td>
</td>
<td>
The prototype of Array iterator objects (<emu-xref href="#sec-array-iterator-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
<ins>%AsyncDisposableStack%</ins>
</td>
<td>
<ins>`AsyncDisposableStack`</ins>
</td>
<td>
<ins>The AsyncDisposableStack constructor (<emu-xref href="#sec-asyncdisposablestack-constructor"></emu-xref>)</ins>
</td>
</tr>
<tr>
<td>
%AsyncFromSyncIteratorPrototype%
</td>
<td>
</td>
<td>
The prototype of async-from-sync iterator objects (<emu-xref href="#sec-async-from-sync-iterator-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
%AsyncFunction%
</td>
<td>
</td>
<td>
The constructor of async function objects (<emu-xref href="#sec-async-function-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%AsyncGeneratorFunction%
</td>
<td>
</td>
<td>
The constructor of async iterator objects (<emu-xref href="#sec-asyncgeneratorfunction-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%AsyncIteratorPrototype%
</td>
<td>
</td>
<td>
An object that all standard built-in async iterator objects indirectly inherit from
</td>
</tr>
<tr>
<td>
%Atomics%
</td>
<td>
`Atomics`
</td>
<td>
The `Atomics` object (<emu-xref href="#sec-atomics-object"></emu-xref>)
</td>
</tr>
<tr>
<td>
%BigInt%
</td>
<td>
`BigInt`
</td>
<td>
The BigInt constructor (<emu-xref href="#sec-bigint-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%BigInt64Array%
</td>
<td>
`BigInt64Array`
</td>
<td>
The BigInt64Array constructor (<emu-xref href="#sec-typedarray-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
%BigUint64Array%
</td>
<td>
`BigUint64Array`
</td>
<td>
The BigUint64Array constructor (<emu-xref href="#sec-typedarray-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Boolean%
</td>
<td>
`Boolean`
</td>
<td>
The Boolean constructor (<emu-xref href="#sec-boolean-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%DataView%
</td>
<td>
`DataView`
</td>
<td>
The DataView constructor (<emu-xref href="#sec-dataview-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Date%
</td>
<td>
`Date`
</td>
<td>
The Date constructor (<emu-xref href="#sec-date-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%decodeURI%
</td>
<td>
`decodeURI`
</td>
<td>
The `decodeURI` function (<emu-xref href="#sec-decodeuri-encodeduri"></emu-xref>)
</td>
</tr>
<tr>
<td>
%decodeURIComponent%
</td>
<td>
`decodeURIComponent`
</td>
<td>
The `decodeURIComponent` function (<emu-xref href="#sec-decodeuricomponent-encodeduricomponent"></emu-xref>)
</td>
</tr>
<tr>
<td>
<ins>%DisposableStack%</ins>
</td>
<td>
<ins>`DisposableStack`</ins>
</td>
<td>
<ins>The DisposableStack constructor (<emu-xref href="#sec-disposablestack-constructor"></emu-xref>)</ins>
</td>
</tr>
<tr>
<td>
%encodeURI%
</td>
<td>
`encodeURI`
</td>
<td>
The `encodeURI` function (<emu-xref href="#sec-encodeuri-uri"></emu-xref>)
</td>
</tr>
<tr>
<td>
%encodeURIComponent%
</td>
<td>
`encodeURIComponent`
</td>
<td>
The `encodeURIComponent` function (<emu-xref href="#sec-encodeuricomponent-uricomponent"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Error%
</td>
<td>
`Error`
</td>
<td>
The Error constructor (<emu-xref href="#sec-error-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%eval%
</td>
<td>
`eval`
</td>
<td>
The `eval` function (<emu-xref href="#sec-eval-x"></emu-xref>)
</td>
</tr>
<tr>
<td>
%EvalError%
</td>
<td>
`EvalError`
</td>
<td>
The EvalError constructor (<emu-xref href="#sec-native-error-types-used-in-this-standard-evalerror"></emu-xref>)
</td>
</tr>
<tr>
<td>
%FinalizationRegistry%
</td>
<td>
`FinalizationRegistry`
</td>
<td>
The FinalizationRegistry constructor (<emu-xref href="#sec-finalization-registry-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Float32Array%
</td>
<td>
`Float32Array`
</td>
<td>
The Float32Array constructor (<emu-xref href="#sec-typedarray-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Float64Array%
</td>
<td>
`Float64Array`
</td>
<td>
The Float64Array constructor (<emu-xref href="#sec-typedarray-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
%ForInIteratorPrototype%
</td>
<td>
</td>
<td>
The prototype of For-In iterator objects (<emu-xref href="#sec-for-in-iterator-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Function%
</td>
<td>
`Function`
</td>
<td>
The Function constructor (<emu-xref href="#sec-function-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%GeneratorFunction%
</td>
<td>
</td>
<td>
The constructor of Generators (<emu-xref href="#sec-generatorfunction-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Int8Array%
</td>
<td>
`Int8Array`
</td>
<td>
The Int8Array constructor (<emu-xref href="#sec-typedarray-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Int16Array%
</td>
<td>
`Int16Array`
</td>
<td>
The Int16Array constructor (<emu-xref href="#sec-typedarray-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Int32Array%
</td>
<td>
`Int32Array`
</td>
<td>
The Int32Array constructor (<emu-xref href="#sec-typedarray-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
%isFinite%
</td>
<td>
`isFinite`
</td>
<td>
The `isFinite` function (<emu-xref href="#sec-isfinite-number"></emu-xref>)
</td>
</tr>
<tr>
<td>
%isNaN%
</td>
<td>
`isNaN`
</td>
<td>
The `isNaN` function (<emu-xref href="#sec-isnan-number"></emu-xref>)
</td>
</tr>
<tr>
<td>
%IteratorPrototype%
</td>
<td>
</td>
<td>
An object that all standard built-in iterator objects indirectly inherit from
</td>
</tr>
<tr>
<td>
%JSON%
</td>
<td>
`JSON`
</td>
<td>
The `JSON` object (<emu-xref href="#sec-json-object"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Map%
</td>
<td>
`Map`
</td>
<td>
The Map constructor (<emu-xref href="#sec-map-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%MapIteratorPrototype%
</td>
<td>
</td>
<td>
The prototype of Map iterator objects (<emu-xref href="#sec-map-iterator-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Math%
</td>
<td>
`Math`
</td>
<td>
The `Math` object (<emu-xref href="#sec-math-object"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Number%
</td>
<td>
`Number`
</td>
<td>
The Number constructor (<emu-xref href="#sec-number-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Object%
</td>
<td>
`Object`
</td>
<td>
The Object constructor (<emu-xref href="#sec-object-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%parseFloat%
</td>
<td>
`parseFloat`
</td>
<td>
The `parseFloat` function (<emu-xref href="#sec-parsefloat-string"></emu-xref>)
</td>
</tr>
<tr>
<td>
%parseInt%
</td>
<td>
`parseInt`
</td>
<td>
The `parseInt` function (<emu-xref href="#sec-parseint-string-radix"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Promise%
</td>
<td>
`Promise`
</td>
<td>
The Promise constructor (<emu-xref href="#sec-promise-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Proxy%
</td>
<td>
`Proxy`
</td>
<td>
The Proxy constructor (<emu-xref href="#sec-proxy-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%RangeError%
</td>
<td>
`RangeError`
</td>
<td>
The RangeError constructor (<emu-xref href="#sec-native-error-types-used-in-this-standard-rangeerror"></emu-xref>)
</td>
</tr>
<tr>
<td>
%ReferenceError%
</td>
<td>
`ReferenceError`
</td>
<td>
The ReferenceError constructor (<emu-xref href="#sec-native-error-types-used-in-this-standard-referenceerror"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Reflect%
</td>
<td>
`Reflect`
</td>
<td>
The `Reflect` object (<emu-xref href="#sec-reflect-object"></emu-xref>)
</td>
</tr>
<tr>
<td>
%RegExp%
</td>
<td>
`RegExp`
</td>
<td>
The RegExp constructor (<emu-xref href="#sec-regexp-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%RegExpStringIteratorPrototype%
</td>
<td>
</td>
<td>
The prototype of RegExp String Iterator objects (<emu-xref href="#sec-regexp-string-iterator-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Set%
</td>
<td>
`Set`
</td>
<td>
The Set constructor (<emu-xref href="#sec-set-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%SetIteratorPrototype%
</td>
<td>
</td>
<td>
The prototype of Set iterator objects (<emu-xref href="#sec-set-iterator-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
%SharedArrayBuffer%
</td>
<td>
`SharedArrayBuffer`
</td>
<td>
The SharedArrayBuffer constructor (<emu-xref href="#sec-sharedarraybuffer-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%String%
</td>
<td>
`String`
</td>
<td>
The String constructor (<emu-xref href="#sec-string-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%StringIteratorPrototype%
</td>
<td>
</td>
<td>
The prototype of String iterator objects (<emu-xref href="#sec-string-iterator-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
<ins>%SuppressedError%</ins>
</td>
<td>
<ins>`SuppressedError`</ins>
</td>
<td>
<ins>The `SuppressedError` constructor (<emu-xref href="#sec-suppressederror-constructor"></emu-xref>)</ins>
</td>
</tr>
<tr>
<td>
%Symbol%
</td>
<td>
`Symbol`
</td>
<td>
The Symbol constructor (<emu-xref href="#sec-symbol-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%SyntaxError%
</td>
<td>
`SyntaxError`
</td>
<td>
The SyntaxError constructor (<emu-xref href="#sec-native-error-types-used-in-this-standard-syntaxerror"></emu-xref>)
</td>
</tr>
<tr>
<td>
%ThrowTypeError%
</td>
<td>
</td>
<td>
A function object that unconditionally throws a new instance of %TypeError%
</td>
</tr>
<tr>
<td>
%TypedArray%
</td>
<td>
</td>
<td>
The super class of all typed Array constructors (<emu-xref href="#sec-%typedarray%-intrinsic-object"></emu-xref>)
</td>
</tr>
<tr>
<td>
%TypeError%
</td>
<td>
`TypeError`
</td>
<td>
The TypeError constructor (<emu-xref href="#sec-native-error-types-used-in-this-standard-typeerror"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Uint8Array%
</td>
<td>
`Uint8Array`
</td>
<td>
The Uint8Array constructor (<emu-xref href="#sec-typedarray-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Uint8ClampedArray%
</td>
<td>
`Uint8ClampedArray`
</td>
<td>
The Uint8ClampedArray constructor (<emu-xref href="#sec-typedarray-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Uint16Array%
</td>
<td>
`Uint16Array`
</td>
<td>
The Uint16Array constructor (<emu-xref href="#sec-typedarray-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
%Uint32Array%
</td>
<td>
`Uint32Array`
</td>
<td>
The Uint32Array constructor (<emu-xref href="#sec-typedarray-objects"></emu-xref>)
</td>
</tr>
<tr>
<td>
%URIError%
</td>
<td>
`URIError`
</td>
<td>
The URIError constructor (<emu-xref href="#sec-native-error-types-used-in-this-standard-urierror"></emu-xref>)
</td>
</tr>
<tr>
<td>
%WeakMap%
</td>
<td>
`WeakMap`
</td>
<td>
The WeakMap constructor (<emu-xref href="#sec-weakmap-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%WeakRef%
</td>
<td>
`WeakRef`
</td>
<td>
The WeakRef constructor (<emu-xref href="#sec-weak-ref-constructor"></emu-xref>)
</td>
</tr>
<tr>
<td>
%WeakSet%
</td>
<td>
`WeakSet`
</td>
<td>
The WeakSet constructor (<emu-xref href="#sec-weakset-constructor"></emu-xref>)
</td>
</tr>
</table>
</emu-table>
</emu-clause>
</emu-clause>
</emu-clause>
<emu-clause id="sec-ecmascript-specification-types">
<h1>ECMAScript Specification Types</h1>
<emu-clause id="sec-reference-record-specification-type" oldids="sec-reference-specification-type">
<h1>The Reference Record Specification Type</h1>
<emu-clause id="sec-initializereferencedbinding" type="abstract operation">
<h1>
InitializeReferencedBinding (
_V_: a Reference Record,
_W_: a Reference Record,
<ins>_hint_: one of ~normal~, ~sync-dispose~, or ~async-dispose~,</ins>
): either a normal completion containing ~unused~ or an abrupt completion
</h1>
<dl class="header">
</dl>
<emu-alg>
1. Assert: IsUnresolvableReference(_V_) is *false*.
1. Let _base_ be _V_.[[Base]].
1. Assert: _base_ is an Environment Record.
1. Return ? _base_.InitializeBinding(_V_.[[ReferencedName]], _W_<ins>, _hint_</ins>).
</emu-alg>
</emu-clause>
</emu-clause>
</emu-clause>
</emu-clause>
<emu-clause id="sec-abstract-operations">
<h1>Abstract Operations</h1>
<ins class="block">
<emu-clause id="sec-operations-on-disposable-objects">
<h1>Operations on Disposable Objects</h1>
<p>See Common Resource Management Interfaces (<emu-xref href="#sec-common-resource-management-interfaces"></emu-xref>).</p>
<emu-clause id="sec-disposecapability-records">
<h1>DisposeCapability Records</h1>
<p>A <dfn variants="DisposeCapability Records">DisposeCapability Record</dfn> is a Record value used to contain a List of DisposableResource Records that are disposed together. DisposeCapability Records are produced by the NewDisposeCapability abstract operation.</p>
<p>DisposeCapability Records have the fields listed in <emu-xref href="#table-disposecapability-record-fields"></emu-xref>:</p>
<emu-table id="table-disposecapability-record-fields" caption="DisposeCapability Record Fields">
<table>
<tbody>
<tr>
<th>
Field Name
</th>
<th>
Value
</th>
<th>
Meaning
</th>
</tr>
<tr>
<td>
[[DisposableResourceStack]]
</td>
<td>
A List of DisposableResource Records.
</td>
<td>
The resources to be disposed. Resources are added in the order they are initialized, and are disposed in reverse order.
</td>
</tr>
</tbody>
</table>
</emu-table>
</emu-clause>
<emu-clause id="sec-disposableresource-records">
<h1>DisposableResource Records</h1>
<p>A <dfn variants="DisposableResource Records">DisposableResource Record</dfn> is a Record value used to encapsulate a disposable object along with the method used to dispose the object. DisposableResource Records are produced by the CreateDisposableResource abstract operation.</p>
<p>DisposableResource Records have the fields listed in <emu-xref href="#table-disposableresource-record-fields"></emu-xref>:</p>
<emu-table id="table-disposableresource-record-fields" caption="DisposableResource Record Fields">
<table>
<tbody>
<tr>
<th>
Field Name
</th>
<th>
Value
</th>
<th>
Meaning
</th>
</tr>
<tr>
<td>
[[ResourceValue]]
</td>
<td>
An Object or *undefined*.
</td>
<td>
The value to be disposed.
</td>
</tr>
<tr>
<td>
[[Hint]]
</td>
<td>
~sync-dispose~ or ~async-dispose~.
</td>
<td>
Indicates whether the resource was added by a `using` declaration or DisposableStack object (~sync-dispose~) or by an `await using` declaration or AsyncDisposableStack object (~async-dispose~).
</td>
</tr>
<tr>
<td>
[[DisposeMethod]]
</td>
<td>
A function object or *undefined*.
</td>
<td>
A function object that will be called with [[ResourceValue]] as its *this* value when the resource disposed.
</td>
</tr>
</tbody>
</table>
</emu-table>
</emu-clause>
<emu-clause id="sec-newdisposecapability" type="abstract operation">
<h1>
NewDisposeCapability (
): a DisposeCapability Record
</h1>
<dl class="header"></dl>
<emu-alg>