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<h1>Node.js v16.16.0 documentation</h1>
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<li><span class="stability_1"><a href="#web-streams-api">Web Streams API</a></span>
<ul>
<li><a href="#overview">Overview</a>
<ul>
<li><a href="#example-readablestream">Example <code>ReadableStream</code></a></li>
</ul>
</li>
<li><a href="#api">API</a>
<ul>
<li><a href="#class-readablestream">Class: <code>ReadableStream</code></a>
<ul>
<li><a href="#new-readablestreamunderlyingsource--strategy"><code>new ReadableStream([underlyingSource [, strategy]])</code></a></li>
<li><a href="#readablestreamlocked"><code>readableStream.locked</code></a></li>
<li><a href="#readablestreamcancelreason"><code>readableStream.cancel([reason])</code></a></li>
<li><a href="#readablestreamgetreaderoptions"><code>readableStream.getReader([options])</code></a></li>
<li><a href="#readablestreampipethroughtransform-options"><code>readableStream.pipeThrough(transform[, options])</code></a></li>
<li><a href="#readablestreampipetodestination-options"><code>readableStream.pipeTo(destination, options)</code></a></li>
<li><a href="#readablestreamtee"><code>readableStream.tee()</code></a></li>
<li><a href="#readablestreamvaluesoptions"><code>readableStream.values([options])</code></a></li>
<li><a href="#async-iteration">Async Iteration</a></li>
<li><a href="#transferring-with-postmessage">Transferring with <code>postMessage()</code></a></li>
</ul>
</li>
<li><a href="#class-readablestreamdefaultreader">Class: <code>ReadableStreamDefaultReader</code></a>
<ul>
<li><a href="#new-readablestreamdefaultreaderstream"><code>new ReadableStreamDefaultReader(stream)</code></a></li>
<li><a href="#readablestreamdefaultreadercancelreason"><code>readableStreamDefaultReader.cancel([reason])</code></a></li>
<li><a href="#readablestreamdefaultreaderclosed"><code>readableStreamDefaultReader.closed</code></a></li>
<li><a href="#readablestreamdefaultreaderread"><code>readableStreamDefaultReader.read()</code></a></li>
<li><a href="#readablestreamdefaultreaderreleaselock"><code>readableStreamDefaultReader.releaseLock()</code></a></li>
</ul>
</li>
<li><a href="#class-readablestreambyobreader">Class: <code>ReadableStreamBYOBReader</code></a>
<ul>
<li><a href="#new-readablestreambyobreaderstream"><code>new ReadableStreamBYOBReader(stream)</code></a></li>
<li><a href="#readablestreambyobreadercancelreason"><code>readableStreamBYOBReader.cancel([reason])</code></a></li>
<li><a href="#readablestreambyobreaderclosed"><code>readableStreamBYOBReader.closed</code></a></li>
<li><a href="#readablestreambyobreaderreadview"><code>readableStreamBYOBReader.read(view)</code></a></li>
<li><a href="#readablestreambyobreaderreleaselock"><code>readableStreamBYOBReader.releaseLock()</code></a></li>
</ul>
</li>
<li><a href="#class-readablestreamdefaultcontroller">Class: <code>ReadableStreamDefaultController</code></a>
<ul>
<li><a href="#readablestreamdefaultcontrollerclose"><code>readableStreamDefaultController.close()</code></a></li>
<li><a href="#readablestreamdefaultcontrollerdesiredsize"><code>readableStreamDefaultController.desiredSize</code></a></li>
<li><a href="#readablestreamdefaultcontrollerenqueuechunk"><code>readableStreamDefaultController.enqueue(chunk)</code></a></li>
<li><a href="#readablestreamdefaultcontrollererrorerror"><code>readableStreamDefaultController.error(error)</code></a></li>
</ul>
</li>
<li><a href="#class-readablebytestreamcontroller">Class: <code>ReadableByteStreamController</code></a>
<ul>
<li><a href="#readablebytestreamcontrollerbyobrequest"><code>readableByteStreamController.byobRequest</code></a></li>
<li><a href="#readablebytestreamcontrollerclose"><code>readableByteStreamController.close()</code></a></li>
<li><a href="#readablebytestreamcontrollerdesiredsize"><code>readableByteStreamController.desiredSize</code></a></li>
<li><a href="#readablebytestreamcontrollerenqueuechunk"><code>readableByteStreamController.enqueue(chunk)</code></a></li>
<li><a href="#readablebytestreamcontrollererrorerror"><code>readableByteStreamController.error(error)</code></a></li>
</ul>
</li>
<li><a href="#class-readablestreambyobrequest">Class: <code>ReadableStreamBYOBRequest</code></a>
<ul>
<li><a href="#readablestreambyobrequestrespondbyteswritten"><code>readableStreamBYOBRequest.respond(bytesWritten)</code></a></li>
<li><a href="#readablestreambyobrequestrespondwithnewviewview"><code>readableStreamBYOBRequest.respondWithNewView(view)</code></a></li>
<li><a href="#readablestreambyobrequestview"><code>readableStreamBYOBRequest.view</code></a></li>
</ul>
</li>
<li><a href="#class-writablestream">Class: <code>WritableStream</code></a>
<ul>
<li><a href="#new-writablestreamunderlyingsink-strategy"><code>new WritableStream([underlyingSink[, strategy]])</code></a></li>
<li><a href="#writablestreamabortreason"><code>writableStream.abort([reason])</code></a></li>
<li><a href="#writablestreamclose"><code>writableStream.close()</code></a></li>
<li><a href="#writablestreamgetwriter"><code>writableStream.getWriter()</code></a></li>
<li><a href="#writablestreamlocked"><code>writableStream.locked</code></a></li>
<li><a href="#transferring-with-postmessage_1">Transferring with postMessage()</a></li>
</ul>
</li>
<li><a href="#class-writablestreamdefaultwriter">Class: <code>WritableStreamDefaultWriter</code></a>
<ul>
<li><a href="#new-writablestreamdefaultwriterstream"><code>new WritableStreamDefaultWriter(stream)</code></a></li>
<li><a href="#writablestreamdefaultwriterabortreason"><code>writableStreamDefaultWriter.abort([reason])</code></a></li>
<li><a href="#writablestreamdefaultwriterclose"><code>writableStreamDefaultWriter.close()</code></a></li>
<li><a href="#writablestreamdefaultwriterclosed"><code>writableStreamDefaultWriter.closed</code></a></li>
<li><a href="#writablestreamdefaultwriterdesiredsize"><code>writableStreamDefaultWriter.desiredSize</code></a></li>
<li><a href="#writablestreamdefaultwriterready"><code>writableStreamDefaultWriter.ready</code></a></li>
<li><a href="#writablestreamdefaultwriterreleaselock"><code>writableStreamDefaultWriter.releaseLock()</code></a></li>
<li><a href="#writablestreamdefaultwriterwritechunk"><code>writableStreamDefaultWriter.write([chunk])</code></a></li>
</ul>
</li>
<li><a href="#class-writablestreamdefaultcontroller">Class: <code>WritableStreamDefaultController</code></a>
<ul>
<li><a href="#writablestreamdefaultcontrollerabortreason"><code>writableStreamDefaultController.abortReason</code></a></li>
<li><a href="#writablestreamdefaultcontrollererrorerror"><code>writableStreamDefaultController.error(error)</code></a></li>
<li><a href="#writablestreamdefaultcontrollersignal"><code>writableStreamDefaultController.signal</code></a></li>
</ul>
</li>
<li><a href="#class-transformstream">Class: <code>TransformStream</code></a>
<ul>
<li><a href="#new-transformstreamtransformer-writablestrategy-readablestrategy"><code>new TransformStream([transformer[, writableStrategy[, readableStrategy]]])</code></a></li>
<li><a href="#transformstreamreadable"><code>transformStream.readable</code></a></li>
<li><a href="#transformstreamwritable"><code>transformStream.writable</code></a></li>
<li><a href="#transferring-with-postmessage_2">Transferring with postMessage()</a></li>
</ul>
</li>
<li><a href="#class-transformstreamdefaultcontroller">Class: <code>TransformStreamDefaultController</code></a>
<ul>
<li><a href="#transformstreamdefaultcontrollerdesiredsize"><code>transformStreamDefaultController.desiredSize</code></a></li>
<li><a href="#transformstreamdefaultcontrollerenqueuechunk"><code>transformStreamDefaultController.enqueue([chunk])</code></a></li>
<li><a href="#transformstreamdefaultcontrollererrorreason"><code>transformStreamDefaultController.error([reason])</code></a></li>
<li><a href="#transformstreamdefaultcontrollerterminate"><code>transformStreamDefaultController.terminate()</code></a></li>
</ul>
</li>
<li><a href="#class-bytelengthqueuingstrategy">Class: <code>ByteLengthQueuingStrategy</code></a>
<ul>
<li><a href="#new-bytelengthqueuingstrategyoptions"><code>new ByteLengthQueuingStrategy(options)</code></a></li>
<li><a href="#bytelengthqueuingstrategyhighwatermark"><code>byteLengthQueuingStrategy.highWaterMark</code></a></li>
<li><a href="#bytelengthqueuingstrategysize"><code>byteLengthQueuingStrategy.size</code></a></li>
</ul>
</li>
<li><a href="#class-countqueuingstrategy">Class: <code>CountQueuingStrategy</code></a>
<ul>
<li><a href="#new-countqueuingstrategyoptions"><code>new CountQueuingStrategy(options)</code></a></li>
<li><a href="#countqueuingstrategyhighwatermark"><code>countQueuingStrategy.highWaterMark</code></a></li>
<li><a href="#countqueuingstrategysize"><code>countQueuingStrategy.size</code></a></li>
</ul>
</li>
<li><a href="#class-textencoderstream">Class: <code>TextEncoderStream</code></a>
<ul>
<li><a href="#new-textencoderstream"><code>new TextEncoderStream()</code></a></li>
<li><a href="#textencoderstreamencoding"><code>textEncoderStream.encoding</code></a></li>
<li><a href="#textencoderstreamreadable"><code>textEncoderStream.readable</code></a></li>
<li><a href="#textencoderstreamwritable"><code>textEncoderStream.writable</code></a></li>
</ul>
</li>
<li><a href="#class-textdecoderstream">Class: <code>TextDecoderStream</code></a>
<ul>
<li><a href="#new-textdecoderstreamencoding-options"><code>new TextDecoderStream([encoding[, options]])</code></a></li>
<li><a href="#textdecoderstreamencoding"><code>textDecoderStream.encoding</code></a></li>
<li><a href="#textdecoderstreamfatal"><code>textDecoderStream.fatal</code></a></li>
<li><a href="#textdecoderstreamignorebom"><code>textDecoderStream.ignoreBOM</code></a></li>
<li><a href="#textdecoderstreamreadable"><code>textDecoderStream.readable</code></a></li>
<li><a href="#textdecoderstreamwritable"><code>textDecoderStream.writable</code></a></li>
</ul>
</li>
<li><a href="#utility-consumers">Utility Consumers</a>
<ul>
<li><a href="#streamconsumersarraybufferstream"><code>streamConsumers.arrayBuffer(stream)</code></a></li>
<li><a href="#streamconsumersblobstream"><code>streamConsumers.blob(stream)</code></a></li>
<li><a href="#streamconsumersbufferstream"><code>streamConsumers.buffer(stream)</code></a></li>
<li><a href="#streamconsumersjsonstream"><code>streamConsumers.json(stream)</code></a></li>
<li><a href="#streamconsumerstextstream"><code>streamConsumers.text(stream)</code></a></li>
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<div class="picker"><ol id="alt-docs"><li><a href="https://nodejs.org/docs/latest-v18.x/api/webstreams.html">18.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v17.x/api/webstreams.html">17.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v16.x/api/webstreams.html">16.x <b>LTS</b></a></li></ol></div>
</li>
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Options
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<ul>
<li>
<a href="all.html">View on single page</a>
</li>
<li>
<a href="webstreams.json">View as JSON</a>
</li>
<li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/master/doc/api/webstreams.md">Edit on GitHub</a></li>
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</ul>
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<hr>
</header>
<details id="toc" open><summary>Table of contents</summary><ul>
<li><span class="stability_1"><a href="#web-streams-api">Web Streams API</a></span>
<ul>
<li><a href="#overview">Overview</a>
<ul>
<li><a href="#example-readablestream">Example <code>ReadableStream</code></a></li>
</ul>
</li>
<li><a href="#api">API</a>
<ul>
<li><a href="#class-readablestream">Class: <code>ReadableStream</code></a>
<ul>
<li><a href="#new-readablestreamunderlyingsource--strategy"><code>new ReadableStream([underlyingSource [, strategy]])</code></a></li>
<li><a href="#readablestreamlocked"><code>readableStream.locked</code></a></li>
<li><a href="#readablestreamcancelreason"><code>readableStream.cancel([reason])</code></a></li>
<li><a href="#readablestreamgetreaderoptions"><code>readableStream.getReader([options])</code></a></li>
<li><a href="#readablestreampipethroughtransform-options"><code>readableStream.pipeThrough(transform[, options])</code></a></li>
<li><a href="#readablestreampipetodestination-options"><code>readableStream.pipeTo(destination, options)</code></a></li>
<li><a href="#readablestreamtee"><code>readableStream.tee()</code></a></li>
<li><a href="#readablestreamvaluesoptions"><code>readableStream.values([options])</code></a></li>
<li><a href="#async-iteration">Async Iteration</a></li>
<li><a href="#transferring-with-postmessage">Transferring with <code>postMessage()</code></a></li>
</ul>
</li>
<li><a href="#class-readablestreamdefaultreader">Class: <code>ReadableStreamDefaultReader</code></a>
<ul>
<li><a href="#new-readablestreamdefaultreaderstream"><code>new ReadableStreamDefaultReader(stream)</code></a></li>
<li><a href="#readablestreamdefaultreadercancelreason"><code>readableStreamDefaultReader.cancel([reason])</code></a></li>
<li><a href="#readablestreamdefaultreaderclosed"><code>readableStreamDefaultReader.closed</code></a></li>
<li><a href="#readablestreamdefaultreaderread"><code>readableStreamDefaultReader.read()</code></a></li>
<li><a href="#readablestreamdefaultreaderreleaselock"><code>readableStreamDefaultReader.releaseLock()</code></a></li>
</ul>
</li>
<li><a href="#class-readablestreambyobreader">Class: <code>ReadableStreamBYOBReader</code></a>
<ul>
<li><a href="#new-readablestreambyobreaderstream"><code>new ReadableStreamBYOBReader(stream)</code></a></li>
<li><a href="#readablestreambyobreadercancelreason"><code>readableStreamBYOBReader.cancel([reason])</code></a></li>
<li><a href="#readablestreambyobreaderclosed"><code>readableStreamBYOBReader.closed</code></a></li>
<li><a href="#readablestreambyobreaderreadview"><code>readableStreamBYOBReader.read(view)</code></a></li>
<li><a href="#readablestreambyobreaderreleaselock"><code>readableStreamBYOBReader.releaseLock()</code></a></li>
</ul>
</li>
<li><a href="#class-readablestreamdefaultcontroller">Class: <code>ReadableStreamDefaultController</code></a>
<ul>
<li><a href="#readablestreamdefaultcontrollerclose"><code>readableStreamDefaultController.close()</code></a></li>
<li><a href="#readablestreamdefaultcontrollerdesiredsize"><code>readableStreamDefaultController.desiredSize</code></a></li>
<li><a href="#readablestreamdefaultcontrollerenqueuechunk"><code>readableStreamDefaultController.enqueue(chunk)</code></a></li>
<li><a href="#readablestreamdefaultcontrollererrorerror"><code>readableStreamDefaultController.error(error)</code></a></li>
</ul>
</li>
<li><a href="#class-readablebytestreamcontroller">Class: <code>ReadableByteStreamController</code></a>
<ul>
<li><a href="#readablebytestreamcontrollerbyobrequest"><code>readableByteStreamController.byobRequest</code></a></li>
<li><a href="#readablebytestreamcontrollerclose"><code>readableByteStreamController.close()</code></a></li>
<li><a href="#readablebytestreamcontrollerdesiredsize"><code>readableByteStreamController.desiredSize</code></a></li>
<li><a href="#readablebytestreamcontrollerenqueuechunk"><code>readableByteStreamController.enqueue(chunk)</code></a></li>
<li><a href="#readablebytestreamcontrollererrorerror"><code>readableByteStreamController.error(error)</code></a></li>
</ul>
</li>
<li><a href="#class-readablestreambyobrequest">Class: <code>ReadableStreamBYOBRequest</code></a>
<ul>
<li><a href="#readablestreambyobrequestrespondbyteswritten"><code>readableStreamBYOBRequest.respond(bytesWritten)</code></a></li>
<li><a href="#readablestreambyobrequestrespondwithnewviewview"><code>readableStreamBYOBRequest.respondWithNewView(view)</code></a></li>
<li><a href="#readablestreambyobrequestview"><code>readableStreamBYOBRequest.view</code></a></li>
</ul>
</li>
<li><a href="#class-writablestream">Class: <code>WritableStream</code></a>
<ul>
<li><a href="#new-writablestreamunderlyingsink-strategy"><code>new WritableStream([underlyingSink[, strategy]])</code></a></li>
<li><a href="#writablestreamabortreason"><code>writableStream.abort([reason])</code></a></li>
<li><a href="#writablestreamclose"><code>writableStream.close()</code></a></li>
<li><a href="#writablestreamgetwriter"><code>writableStream.getWriter()</code></a></li>
<li><a href="#writablestreamlocked"><code>writableStream.locked</code></a></li>
<li><a href="#transferring-with-postmessage_1">Transferring with postMessage()</a></li>
</ul>
</li>
<li><a href="#class-writablestreamdefaultwriter">Class: <code>WritableStreamDefaultWriter</code></a>
<ul>
<li><a href="#new-writablestreamdefaultwriterstream"><code>new WritableStreamDefaultWriter(stream)</code></a></li>
<li><a href="#writablestreamdefaultwriterabortreason"><code>writableStreamDefaultWriter.abort([reason])</code></a></li>
<li><a href="#writablestreamdefaultwriterclose"><code>writableStreamDefaultWriter.close()</code></a></li>
<li><a href="#writablestreamdefaultwriterclosed"><code>writableStreamDefaultWriter.closed</code></a></li>
<li><a href="#writablestreamdefaultwriterdesiredsize"><code>writableStreamDefaultWriter.desiredSize</code></a></li>
<li><a href="#writablestreamdefaultwriterready"><code>writableStreamDefaultWriter.ready</code></a></li>
<li><a href="#writablestreamdefaultwriterreleaselock"><code>writableStreamDefaultWriter.releaseLock()</code></a></li>
<li><a href="#writablestreamdefaultwriterwritechunk"><code>writableStreamDefaultWriter.write([chunk])</code></a></li>
</ul>
</li>
<li><a href="#class-writablestreamdefaultcontroller">Class: <code>WritableStreamDefaultController</code></a>
<ul>
<li><a href="#writablestreamdefaultcontrollerabortreason"><code>writableStreamDefaultController.abortReason</code></a></li>
<li><a href="#writablestreamdefaultcontrollererrorerror"><code>writableStreamDefaultController.error(error)</code></a></li>
<li><a href="#writablestreamdefaultcontrollersignal"><code>writableStreamDefaultController.signal</code></a></li>
</ul>
</li>
<li><a href="#class-transformstream">Class: <code>TransformStream</code></a>
<ul>
<li><a href="#new-transformstreamtransformer-writablestrategy-readablestrategy"><code>new TransformStream([transformer[, writableStrategy[, readableStrategy]]])</code></a></li>
<li><a href="#transformstreamreadable"><code>transformStream.readable</code></a></li>
<li><a href="#transformstreamwritable"><code>transformStream.writable</code></a></li>
<li><a href="#transferring-with-postmessage_2">Transferring with postMessage()</a></li>
</ul>
</li>
<li><a href="#class-transformstreamdefaultcontroller">Class: <code>TransformStreamDefaultController</code></a>
<ul>
<li><a href="#transformstreamdefaultcontrollerdesiredsize"><code>transformStreamDefaultController.desiredSize</code></a></li>
<li><a href="#transformstreamdefaultcontrollerenqueuechunk"><code>transformStreamDefaultController.enqueue([chunk])</code></a></li>
<li><a href="#transformstreamdefaultcontrollererrorreason"><code>transformStreamDefaultController.error([reason])</code></a></li>
<li><a href="#transformstreamdefaultcontrollerterminate"><code>transformStreamDefaultController.terminate()</code></a></li>
</ul>
</li>
<li><a href="#class-bytelengthqueuingstrategy">Class: <code>ByteLengthQueuingStrategy</code></a>
<ul>
<li><a href="#new-bytelengthqueuingstrategyoptions"><code>new ByteLengthQueuingStrategy(options)</code></a></li>
<li><a href="#bytelengthqueuingstrategyhighwatermark"><code>byteLengthQueuingStrategy.highWaterMark</code></a></li>
<li><a href="#bytelengthqueuingstrategysize"><code>byteLengthQueuingStrategy.size</code></a></li>
</ul>
</li>
<li><a href="#class-countqueuingstrategy">Class: <code>CountQueuingStrategy</code></a>
<ul>
<li><a href="#new-countqueuingstrategyoptions"><code>new CountQueuingStrategy(options)</code></a></li>
<li><a href="#countqueuingstrategyhighwatermark"><code>countQueuingStrategy.highWaterMark</code></a></li>
<li><a href="#countqueuingstrategysize"><code>countQueuingStrategy.size</code></a></li>
</ul>
</li>
<li><a href="#class-textencoderstream">Class: <code>TextEncoderStream</code></a>
<ul>
<li><a href="#new-textencoderstream"><code>new TextEncoderStream()</code></a></li>
<li><a href="#textencoderstreamencoding"><code>textEncoderStream.encoding</code></a></li>
<li><a href="#textencoderstreamreadable"><code>textEncoderStream.readable</code></a></li>
<li><a href="#textencoderstreamwritable"><code>textEncoderStream.writable</code></a></li>
</ul>
</li>
<li><a href="#class-textdecoderstream">Class: <code>TextDecoderStream</code></a>
<ul>
<li><a href="#new-textdecoderstreamencoding-options"><code>new TextDecoderStream([encoding[, options]])</code></a></li>
<li><a href="#textdecoderstreamencoding"><code>textDecoderStream.encoding</code></a></li>
<li><a href="#textdecoderstreamfatal"><code>textDecoderStream.fatal</code></a></li>
<li><a href="#textdecoderstreamignorebom"><code>textDecoderStream.ignoreBOM</code></a></li>
<li><a href="#textdecoderstreamreadable"><code>textDecoderStream.readable</code></a></li>
<li><a href="#textdecoderstreamwritable"><code>textDecoderStream.writable</code></a></li>
</ul>
</li>
<li><a href="#utility-consumers">Utility Consumers</a>
<ul>
<li><a href="#streamconsumersarraybufferstream"><code>streamConsumers.arrayBuffer(stream)</code></a></li>
<li><a href="#streamconsumersblobstream"><code>streamConsumers.blob(stream)</code></a></li>
<li><a href="#streamconsumersbufferstream"><code>streamConsumers.buffer(stream)</code></a></li>
<li><a href="#streamconsumersjsonstream"><code>streamConsumers.json(stream)</code></a></li>
<li><a href="#streamconsumerstextstream"><code>streamConsumers.text(stream)</code></a></li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
</ul></details>
<div id="apicontent">
<h2>Web Streams API<span><a class="mark" href="#web-streams-api" id="web-streams-api">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_web_streams_api"></a></h2>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<p>An implementation of the <a href="https://streams.spec.whatwg.org/">WHATWG Streams Standard</a>.</p>
<pre><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> {
<span class="hljs-title class_">ReadableStream</span>,
<span class="hljs-title class_">WritableStream</span>,
<span class="hljs-title class_">TransformStream</span>,
} <span class="hljs-keyword">from</span> <span class="hljs-string">'node:stream/web'</span>;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> {
<span class="hljs-title class_">ReadableStream</span>,
<span class="hljs-title class_">WritableStream</span>,
<span class="hljs-title class_">TransformStream</span>,
} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'stream/web'</span>);</code></pre>
<section><h3>Overview<span><a class="mark" href="#overview" id="overview">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_overview"></a></h3>
<p>The <a href="https://streams.spec.whatwg.org/">WHATWG Streams Standard</a> (or "web streams") defines an API for handling
streaming data. It is similar to the Node.js <a href="stream.html">Streams</a> API but emerged later
and has become the "standard" API for streaming data across many JavaScript
environments.</p>
<p>There are three primary types of objects</p>
<ul>
<li><code>ReadableStream</code> - Represents a source of streaming data.</li>
<li><code>WritableStream</code> - Represents a destination for streaming data.</li>
<li><code>TransformStream</code> - Represents an algorithm for transforming streaming data.</li>
</ul>
<h4>Example <code>ReadableStream</code><span><a class="mark" href="#example-readablestream" id="example-readablestream">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_example_readablestream"></a></h4>
<p>This example creates a simple <code>ReadableStream</code> that pushes the current
<code>performance.now()</code> timestamp once every second forever. An async iterable
is used to read the data from the stream.</p>
<pre><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> {
<span class="hljs-title class_">ReadableStream</span>
} <span class="hljs-keyword">from</span> <span class="hljs-string">'node:stream/web'</span>;
<span class="hljs-keyword">import</span> {
<span class="hljs-built_in">setInterval</span> <span class="hljs-keyword">as</span> every
} <span class="hljs-keyword">from</span> <span class="hljs-string">'node:timers/promises'</span>;
<span class="hljs-keyword">import</span> {
performance
} <span class="hljs-keyword">from</span> <span class="hljs-string">'node:perf_hooks'</span>;
<span class="hljs-keyword">const</span> <span class="hljs-variable constant_">SECOND</span> = <span class="hljs-number">1000</span>;
<span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">ReadableStream</span>({
<span class="hljs-keyword">async</span> <span class="hljs-title function_">start</span>(<span class="hljs-params">controller</span>) {
<span class="hljs-keyword">for</span> <span class="hljs-keyword">await</span> (<span class="hljs-keyword">const</span> _ <span class="hljs-keyword">of</span> <span class="hljs-title function_">every</span>(<span class="hljs-variable constant_">SECOND</span>))
controller.<span class="hljs-title function_">enqueue</span>(performance.<span class="hljs-title function_">now</span>());
}
});
<span class="hljs-keyword">for</span> <span class="hljs-keyword">await</span> (<span class="hljs-keyword">const</span> value <span class="hljs-keyword">of</span> stream)
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(value);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> {
<span class="hljs-title class_">ReadableStream</span>
} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'stream/web'</span>);
<span class="hljs-keyword">const</span> {
<span class="hljs-attr">setInterval</span>: every
} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'timers/promises'</span>);
<span class="hljs-keyword">const</span> {
performance
} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>);
<span class="hljs-keyword">const</span> <span class="hljs-variable constant_">SECOND</span> = <span class="hljs-number">1000</span>;
<span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">ReadableStream</span>({
<span class="hljs-keyword">async</span> <span class="hljs-title function_">start</span>(<span class="hljs-params">controller</span>) {
<span class="hljs-keyword">for</span> <span class="hljs-keyword">await</span> (<span class="hljs-keyword">const</span> _ <span class="hljs-keyword">of</span> <span class="hljs-title function_">every</span>(<span class="hljs-variable constant_">SECOND</span>))
controller.<span class="hljs-title function_">enqueue</span>(performance.<span class="hljs-title function_">now</span>());
}
});
(<span class="hljs-keyword">async</span> () => {
<span class="hljs-keyword">for</span> <span class="hljs-keyword">await</span> (<span class="hljs-keyword">const</span> value <span class="hljs-keyword">of</span> stream)
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(value);
})();</code></pre>
</section><section><h3>API<span><a class="mark" href="#api" id="api">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_api"></a></h3>
<h4>Class: <code>ReadableStream</code><span><a class="mark" href="#class-readablestream" id="class-readablestream">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_class_readablestream"></a></h4>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<h5><code>new ReadableStream([underlyingSource [, strategy]])</code><span><a class="mark" href="#new-readablestreamunderlyingsource--strategy" id="new-readablestreamunderlyingsource--strategy">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_new_readablestream_underlyingsource_strategy"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<!--lint disable maximum-line-length remark-lint-->
<ul>
<li><code>underlyingSource</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>start</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A user-defined function that is invoked immediately when
the <code>ReadableStream</code> is created.
<ul>
<li><code>controller</code> <a href="webstreams.html#class-readablestreamdefaultcontroller" class="type"><ReadableStreamDefaultController></a> | <a href="webstreams.html#class-readablebytestreamcontroller" class="type"><ReadableByteStreamController></a></li>
<li>Returns: <code>undefined</code> or a promise fulfilled with <code>undefined</code>.</li>
</ul>
</li>
<li><code>pull</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A user-defined function that is called repeatedly when the
<code>ReadableStream</code> internal queue is not full. The operation may be sync or
async. If async, the function will not be called again until the previously
returned promise is fulfilled.
<ul>
<li><code>controller</code> <a href="webstreams.html#class-readablestreamdefaultcontroller" class="type"><ReadableStreamDefaultController></a> | <a href="webstreams.html#class-readablebytestreamcontroller" class="type"><ReadableByteStreamController></a></li>
<li>Returns: A promise fulfilled with <code>undefined</code>.</li>
</ul>
</li>
<li><code>cancel</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A user-defined function that is called when the
<code>ReadableStream</code> is canceled.
<ul>
<li><code>reason</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: A promise fulfilled with <code>undefined</code>.</li>
</ul>
</li>
<li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Must be <code>'bytes'</code> or <code>undefined</code>.</li>
<li><code>autoAllocateChunkSize</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> Used only when <code>type</code> is equal to
<code>'bytes'</code>.</li>
</ul>
</li>
<li><code>strategy</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>highWaterMark</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The maximum internal queue size before backpressure
is applied.</li>
<li><code>size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A user-defined function used to identify the size of each
chunk of data.
<ul>
<li><code>chunk</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
</ul>
</li>
</ul>
</li>
</ul>
<!--lint enable maximum-line-length remark-lint-->
<h5><code>readableStream.locked</code><span><a class="mark" href="#readablestreamlocked" id="readablestreamlocked">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestream_locked"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Set to <code>true</code> if there is an active reader for this
<a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a>.</li>
</ul>
<p>The <code>readableStream.locked</code> property is <code>false</code> by default, and is
switched to <code>true</code> while there is an active reader consuming the
stream's data.</p>
<h5><code>readableStream.cancel([reason])</code><span><a class="mark" href="#readablestreamcancelreason" id="readablestreamcancelreason">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestream_cancel_reason"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>reason</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: A promise fulfilled with <code>undefined</code> once cancelation has
been completed.</li>
</ul>
<h5><code>readableStream.getReader([options])</code><span><a class="mark" href="#readablestreamgetreaderoptions" id="readablestreamgetreaderoptions">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestream_getreader_options"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>mode</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> <code>'byob'</code> or <code>undefined</code></li>
</ul>
</li>
<li>Returns: <a href="webstreams.html#class-readablestreamdefaultreader" class="type"><ReadableStreamDefaultReader></a> | <a href="webstreams.html#class-readablestreambyobreader" class="type"><ReadableStreamBYOBReader></a></li>
</ul>
<pre><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">ReadableStream</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:stream/web'</span>;
<span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">ReadableStream</span>();
<span class="hljs-keyword">const</span> reader = stream.<span class="hljs-title function_">getReader</span>();
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-keyword">await</span> reader.<span class="hljs-title function_">read</span>());</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">ReadableStream</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'stream/web'</span>);
<span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">ReadableStream</span>();
<span class="hljs-keyword">const</span> reader = stream.<span class="hljs-title function_">getReader</span>();
reader.<span class="hljs-title function_">read</span>().<span class="hljs-title function_">then</span>(<span class="hljs-variable language_">console</span>.<span class="hljs-property">log</span>);</code></pre>
<p>Causes the <code>readableStream.locked</code> to be <code>true</code>.</p>
<h5><code>readableStream.pipeThrough(transform[, options])</code><span><a class="mark" href="#readablestreampipethroughtransform-options" id="readablestreampipethroughtransform-options">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestream_pipethrough_transform_options"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>transform</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>readable</code> <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> The <code>ReadableStream</code> to which
<code>transform.writable</code> will push the potentially modified data
is receives from this <code>ReadableStream</code>.</li>
<li><code>writable</code> <a href="webstreams.html#class-writablestream" class="type"><WritableStream></a> The <code>WritableStream</code> to which this
<code>ReadableStream</code>'s data will be written.</li>
</ul>
</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>preventAbort</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> When <code>true</code>, errors in this <code>ReadableStream</code>
will not cause <code>transform.writable</code> to be aborted.</li>
<li><code>preventCancel</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> When <code>true</code>, errors in the destination
<code>transform.writable</code> is not cause this <code>ReadableStream</code> to be
canceled.</li>
<li><code>preventClose</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> When <code>true</code>, closing this <code>ReadableStream</code>
will no cause <code>transform.writable</code> to be closed.</li>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type"><AbortSignal></a> Allows the transfer of data to be canceled
using an <a href="globals.html#class-abortcontroller" class="type"><AbortController></a>.</li>
</ul>
</li>
<li>Returns: <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> From <code>transform.readable</code>.</li>
</ul>
<p>Connects this <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> to the pair of <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> and
<a href="webstreams.html#class-writablestream" class="type"><WritableStream></a> provided in the <code>transform</code> argument such that the
data from this <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> is written in to <code>transform.writable</code>,
possibly transformed, then pushed to <code>transform.readable</code>. Once the
pipeline is configured, <code>transform.readable</code> is returned.</p>
<p>Causes the <code>readableStream.locked</code> to be <code>true</code> while the pipe operation
is active.</p>
<pre><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> {
<span class="hljs-title class_">ReadableStream</span>,
<span class="hljs-title class_">TransformStream</span>,
} <span class="hljs-keyword">from</span> <span class="hljs-string">'node:stream/web'</span>;
<span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">ReadableStream</span>({
<span class="hljs-title function_">start</span>(<span class="hljs-params">controller</span>) {
controller.<span class="hljs-title function_">enqueue</span>(<span class="hljs-string">'a'</span>);
},
});
<span class="hljs-keyword">const</span> transform = <span class="hljs-keyword">new</span> <span class="hljs-title class_">TransformStream</span>({
<span class="hljs-title function_">transform</span>(<span class="hljs-params">chunk, controller</span>) {
controller.<span class="hljs-title function_">enqueue</span>(chunk.<span class="hljs-title function_">toUpperCase</span>());
}
});
<span class="hljs-keyword">const</span> transformedStream = stream.<span class="hljs-title function_">pipeThrough</span>(transform);
<span class="hljs-keyword">for</span> <span class="hljs-keyword">await</span> (<span class="hljs-keyword">const</span> chunk <span class="hljs-keyword">of</span> transformedStream)
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(chunk);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> {
<span class="hljs-title class_">ReadableStream</span>,
<span class="hljs-title class_">TransformStream</span>,
} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'stream/web'</span>);
<span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">ReadableStream</span>({
<span class="hljs-title function_">start</span>(<span class="hljs-params">controller</span>) {
controller.<span class="hljs-title function_">enqueue</span>(<span class="hljs-string">'a'</span>);
},
});
<span class="hljs-keyword">const</span> transform = <span class="hljs-keyword">new</span> <span class="hljs-title class_">TransformStream</span>({
<span class="hljs-title function_">transform</span>(<span class="hljs-params">chunk, controller</span>) {
controller.<span class="hljs-title function_">enqueue</span>(chunk.<span class="hljs-title function_">toUpperCase</span>());
}
});
<span class="hljs-keyword">const</span> transformedStream = stream.<span class="hljs-title function_">pipeThrough</span>(transform);
(<span class="hljs-keyword">async</span> () => {
<span class="hljs-keyword">for</span> <span class="hljs-keyword">await</span> (<span class="hljs-keyword">const</span> chunk <span class="hljs-keyword">of</span> transformedStream)
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(chunk);
})();</code></pre>
<h5><code>readableStream.pipeTo(destination, options)</code><span><a class="mark" href="#readablestreampipetodestination-options" id="readablestreampipetodestination-options">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestream_pipeto_destination_options"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>destination</code> <a href="webstreams.html#class-writablestream" class="type"><WritableStream></a> A <a href="webstreams.html#class-writablestream" class="type"><WritableStream></a> to which this
<code>ReadableStream</code>'s data will be written.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>preventAbort</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> When <code>true</code>, errors in this <code>ReadableStream</code>
will not cause <code>transform.writable</code> to be aborted.</li>
<li><code>preventCancel</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> When <code>true</code>, errors in the destination
<code>transform.writable</code> is not cause this <code>ReadableStream</code> to be
canceled.</li>
<li><code>preventClose</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> When <code>true</code>, closing this <code>ReadableStream</code>
will no cause <code>transform.writable</code> to be closed.</li>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type"><AbortSignal></a> Allows the transfer of data to be canceled
using an <a href="globals.html#class-abortcontroller" class="type"><AbortController></a>.</li>
</ul>
</li>
<li>Returns: A promise fulfilled with <code>undefined</code></li>
</ul>
<p>Causes the <code>readableStream.locked</code> to be <code>true</code> while the pipe operation
is active.</p>
<h5><code>readableStream.tee()</code><span><a class="mark" href="#readablestreamtee" id="readablestreamtee">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestream_tee"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Returns: <a href="webstreams.html#class-readablestream" class="type"><ReadableStream[]></a></li>
</ul>
<p>Returns a pair of new <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> instances to which this
<code>ReadableStream</code>'s data will be forwarded. Each will receive the
same data.</p>
<p>Causes the <code>readableStream.locked</code> to be <code>true</code>.</p>
<h5><code>readableStream.values([options])</code><span><a class="mark" href="#readablestreamvaluesoptions" id="readablestreamvaluesoptions">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestream_values_options"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>preventCancel</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> When <code>true</code>, prevents the <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a>
from being closed when the async iterator abruptly terminates.
<strong>Defaults</strong>: <code>false</code></li>
</ul>
</li>
</ul>
<p>Creates and returns an async iterator usable for consuming this
<code>ReadableStream</code>'s data.</p>
<p>Causes the <code>readableStream.locked</code> to be <code>true</code> while the async iterator
is active.</p>
<pre><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">Buffer</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:buffer'</span>;
<span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">ReadableStream</span>(<span class="hljs-title function_">getSomeSource</span>());
<span class="hljs-keyword">for</span> <span class="hljs-keyword">await</span> (<span class="hljs-keyword">const</span> chunk <span class="hljs-keyword">of</span> stream.<span class="hljs-title function_">values</span>({ <span class="hljs-attr">preventCancel</span>: <span class="hljs-literal">true</span> }))
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title class_">Buffer</span>.<span class="hljs-title function_">from</span>(chunk).<span class="hljs-title function_">toString</span>());</code></pre>
<h5>Async Iteration<span><a class="mark" href="#async-iteration" id="async-iteration">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_async_iteration"></a></h5>
<p>The <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> object supports the async iterator protocol using
<code>for await</code> syntax.</p>
<pre><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">Buffer</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'buffer'</span>;
<span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">ReadableStream</span>(<span class="hljs-title function_">getSomeSource</span>());
<span class="hljs-keyword">for</span> <span class="hljs-keyword">await</span> (<span class="hljs-keyword">const</span> chunk <span class="hljs-keyword">of</span> stream)
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title class_">Buffer</span>.<span class="hljs-title function_">from</span>(chunk).<span class="hljs-title function_">toString</span>());</code></pre>
<p>The async iterator will consume the <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> until it terminates.</p>
<p>By default, if the async iterator exits early (via either a <code>break</code>,
<code>return</code>, or a <code>throw</code>), the <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> will be closed. To prevent
automatic closing of the <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a>, use the <code>readableStream.values()</code>
method to acquire the async iterator and set the <code>preventCancel</code> option to
<code>true</code>.</p>
<p>The <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> must not be locked (that is, it must not have an existing
active reader). During the async iteration, the <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> will be locked.</p>
<h5>Transferring with <code>postMessage()</code><span><a class="mark" href="#transferring-with-postmessage" id="transferring-with-postmessage">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_transferring_with_postmessage"></a></h5>
<p>A <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> instance can be transferred using a <a href="worker_threads.html#class-messageport" class="type"><MessagePort></a>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">ReadableStream</span>(<span class="hljs-title function_">getReadableSourceSomehow</span>());
<span class="hljs-keyword">const</span> { port1, port2 } = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MessageChannel</span>();
port1.<span class="hljs-property">onmessage</span> = <span class="hljs-function">(<span class="hljs-params">{ data }</span>) =></span> {
data.<span class="hljs-title function_">getReader</span>().<span class="hljs-title function_">read</span>().<span class="hljs-title function_">then</span>(<span class="hljs-function">(<span class="hljs-params">chunk</span>) =></span> {
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(chunk);
});
};
port2.<span class="hljs-title function_">postMessage</span>(stream, [stream]);</code></pre>
<h4>Class: <code>ReadableStreamDefaultReader</code><span><a class="mark" href="#class-readablestreamdefaultreader" id="class-readablestreamdefaultreader">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_class_readablestreamdefaultreader"></a></h4>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<p>By default, calling <code>readableStream.getReader()</code> with no arguments
will return an instance of <code>ReadableStreamDefaultReader</code>. The default
reader treats the chunks of data passed through the stream as opaque
values, which allows the <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> to work with generally any
JavaScript value.</p>
<h5><code>new ReadableStreamDefaultReader(stream)</code><span><a class="mark" href="#new-readablestreamdefaultreaderstream" id="new-readablestreamdefaultreaderstream">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_new_readablestreamdefaultreader_stream"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>stream</code> <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a></li>
</ul>
<p>Creates a new <a href="webstreams.html#class-readablestreamdefaultreader" class="type"><ReadableStreamDefaultReader></a> that is locked to the
given <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a>.</p>
<h5><code>readableStreamDefaultReader.cancel([reason])</code><span><a class="mark" href="#readablestreamdefaultreadercancelreason" id="readablestreamdefaultreadercancelreason">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestreamdefaultreader_cancel_reason"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>reason</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: A promise fulfilled with <code>undefined</code>.</li>
</ul>
<p>Cancels the <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> and returns a promise that is fulfilled
when the underlying stream has been canceled.</p>
<h5><code>readableStreamDefaultReader.closed</code><span><a class="mark" href="#readablestreamdefaultreaderclosed" id="readablestreamdefaultreaderclosed">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestreamdefaultreader_closed"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a> Fulfilled with <code>undefined</code> when the associated
<a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> is closed or rejected if the stream errors or the reader's
lock is released before the stream finishes closing.</li>
</ul>
<h5><code>readableStreamDefaultReader.read()</code><span><a class="mark" href="#readablestreamdefaultreaderread" id="readablestreamdefaultreaderread">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestreamdefaultreader_read"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Returns: A promise fulfilled with an object:
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer" class="type"><ArrayBuffer></a></li>
<li><code>done</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
</li>
</ul>
<p>Requests the next chunk of data from the underlying <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a>
and returns a promise that is fulfilled with the data once it is
available.</p>
<h5><code>readableStreamDefaultReader.releaseLock()</code><span><a class="mark" href="#readablestreamdefaultreaderreleaselock" id="readablestreamdefaultreaderreleaselock">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestreamdefaultreader_releaselock"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<p>Releases this reader's lock on the underlying <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a>.</p>
<h4>Class: <code>ReadableStreamBYOBReader</code><span><a class="mark" href="#class-readablestreambyobreader" id="class-readablestreambyobreader">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_class_readablestreambyobreader"></a></h4>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<p>The <code>ReadableStreamBYOBReader</code> is an alternative consumer for
byte-oriented <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a>'s (those that are created with
<code>underlyingSource.type</code> set equal to <code>'bytes'</code> when the
<code>ReadableStream</code> was created).</p>
<p>The <code>BYOB</code> is short for "bring your own buffer". This is a
pattern that allows for more efficient reading of byte-oriented
data that avoids extraneous copying.</p>
<pre><code class="language-js mjs"><span class="hljs-keyword">import</span> {
open
} <span class="hljs-keyword">from</span> <span class="hljs-string">'node:fs/promises'</span>;
<span class="hljs-keyword">import</span> {
<span class="hljs-title class_">ReadableStream</span>
} <span class="hljs-keyword">from</span> <span class="hljs-string">'node:stream/web'</span>;
<span class="hljs-keyword">import</span> { <span class="hljs-title class_">Buffer</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:buffer'</span>;
<span class="hljs-keyword">class</span> <span class="hljs-title class_">Source</span> {
type = <span class="hljs-string">'bytes'</span>;
autoAllocateChunkSize = <span class="hljs-number">1024</span>;
<span class="hljs-keyword">async</span> <span class="hljs-title function_">start</span>(<span class="hljs-params">controller</span>) {
<span class="hljs-variable language_">this</span>.<span class="hljs-property">file</span> = <span class="hljs-keyword">await</span> <span class="hljs-title function_">open</span>(<span class="hljs-keyword">new</span> <span class="hljs-title function_">URL</span>(<span class="hljs-keyword">import</span>.<span class="hljs-property">meta</span>.<span class="hljs-property">url</span>));
<span class="hljs-variable language_">this</span>.<span class="hljs-property">controller</span> = controller;
}
<span class="hljs-keyword">async</span> <span class="hljs-title function_">pull</span>(<span class="hljs-params">controller</span>) {
<span class="hljs-keyword">const</span> view = controller.<span class="hljs-property">byobRequest</span>?.<span class="hljs-property">view</span>;
<span class="hljs-keyword">const</span> {
bytesRead,
} = <span class="hljs-keyword">await</span> <span class="hljs-variable language_">this</span>.<span class="hljs-property">file</span>.<span class="hljs-title function_">read</span>({
<span class="hljs-attr">buffer</span>: view,
<span class="hljs-attr">offset</span>: view.<span class="hljs-property">byteOffset</span>,
<span class="hljs-attr">length</span>: view.<span class="hljs-property">byteLength</span>
});
<span class="hljs-keyword">if</span> (bytesRead === <span class="hljs-number">0</span>) {
<span class="hljs-keyword">await</span> <span class="hljs-variable language_">this</span>.<span class="hljs-property">file</span>.<span class="hljs-title function_">close</span>();
<span class="hljs-variable language_">this</span>.<span class="hljs-property">controller</span>.<span class="hljs-title function_">close</span>();
}
controller.<span class="hljs-property">byobRequest</span>.<span class="hljs-title function_">respond</span>(bytesRead);
}
}
<span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">ReadableStream</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Source</span>());
<span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">read</span>(<span class="hljs-params">stream</span>) {
<span class="hljs-keyword">const</span> reader = stream.<span class="hljs-title function_">getReader</span>({ <span class="hljs-attr">mode</span>: <span class="hljs-string">'byob'</span> });
<span class="hljs-keyword">const</span> chunks = [];
<span class="hljs-keyword">let</span> result;
<span class="hljs-keyword">do</span> {
result = <span class="hljs-keyword">await</span> reader.<span class="hljs-title function_">read</span>(<span class="hljs-title class_">Buffer</span>.<span class="hljs-title function_">alloc</span>(<span class="hljs-number">100</span>));
<span class="hljs-keyword">if</span> (result.<span class="hljs-property">value</span> !== <span class="hljs-literal">undefined</span>)
chunks.<span class="hljs-title function_">push</span>(<span class="hljs-title class_">Buffer</span>.<span class="hljs-title function_">from</span>(result.<span class="hljs-property">value</span>));
} <span class="hljs-keyword">while</span> (!result.<span class="hljs-property">done</span>);
<span class="hljs-keyword">return</span> <span class="hljs-title class_">Buffer</span>.<span class="hljs-title function_">concat</span>(chunks);
}
<span class="hljs-keyword">const</span> data = <span class="hljs-keyword">await</span> <span class="hljs-title function_">read</span>(stream);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title class_">Buffer</span>.<span class="hljs-title function_">from</span>(data).<span class="hljs-title function_">toString</span>());</code></pre>
<h5><code>new ReadableStreamBYOBReader(stream)</code><span><a class="mark" href="#new-readablestreambyobreaderstream" id="new-readablestreambyobreaderstream">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_new_readablestreambyobreader_stream"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>stream</code> <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a></li>
</ul>
<p>Creates a new <code>ReadableStreamBYOBReader</code> that is locked to the
given <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a>.</p>
<h5><code>readableStreamBYOBReader.cancel([reason])</code><span><a class="mark" href="#readablestreambyobreadercancelreason" id="readablestreambyobreadercancelreason">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestreambyobreader_cancel_reason"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>reason</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: A promise fulfilled with <code>undefined</code>.</li>
</ul>
<p>Cancels the <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> and returns a promise that is fulfilled
when the underlying stream has been canceled.</p>
<h5><code>readableStreamBYOBReader.closed</code><span><a class="mark" href="#readablestreambyobreaderclosed" id="readablestreambyobreaderclosed">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestreambyobreader_closed"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a> Fulfilled with <code>undefined</code> when the associated
<a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> is closed or rejected if the stream errors or the reader's
lock is released before the stream finishes closing.</li>
</ul>
<h5><code>readableStreamBYOBReader.read(view)</code><span><a class="mark" href="#readablestreambyobreaderreadview" id="readablestreambyobreaderreadview">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestreambyobreader_read_view"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>view</code> <a href="buffer.html#class-buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray" class="type"><TypedArray></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView" class="type"><DataView></a></li>
<li>Returns: A promise fulfilled with an object:
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer" class="type"><ArrayBuffer></a></li>
<li><code>done</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
</li>
</ul>
<p>Requests the next chunk of data from the underlying <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a>
and returns a promise that is fulfilled with the data once it is
available.</p>
<p>Do not pass a pooled <a href="buffer.html#class-buffer" class="type"><Buffer></a> object instance in to this method.
Pooled <code>Buffer</code> objects are created using <code>Buffer.allocUnsafe()</code>,
or <code>Buffer.from()</code>, or are often returned by various <code>fs</code> module
callbacks. These types of <code>Buffer</code>s use a shared underlying
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer" class="type"><ArrayBuffer></a> object that contains all of the data from all of
the pooled <code>Buffer</code> instances. When a <code>Buffer</code>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray" class="type"><TypedArray></a>,
or <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView" class="type"><DataView></a> is passed in to <code>readableStreamBYOBReader.read()</code>,
the view's underlying <code>ArrayBuffer</code> is <em>detached</em>, invalidating
all existing views that may exist on that <code>ArrayBuffer</code>. This
can have disastrous consequences for your application.</p>
<h5><code>readableStreamBYOBReader.releaseLock()</code><span><a class="mark" href="#readablestreambyobreaderreleaselock" id="readablestreambyobreaderreleaselock">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestreambyobreader_releaselock"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<p>Releases this reader's lock on the underlying <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a>.</p>
<h4>Class: <code>ReadableStreamDefaultController</code><span><a class="mark" href="#class-readablestreamdefaultcontroller" id="class-readablestreamdefaultcontroller">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_class_readablestreamdefaultcontroller"></a></h4>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<p>Every <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> has a controller that is responsible for
the internal state and management of the stream's queue. The
<code>ReadableStreamDefaultController</code> is the default controller
implementation for <code>ReadableStream</code>s that are not byte-oriented.</p>
<h5><code>readableStreamDefaultController.close()</code><span><a class="mark" href="#readablestreamdefaultcontrollerclose" id="readablestreamdefaultcontrollerclose">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestreamdefaultcontroller_close"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<p>Closes the <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> to which this controller is associated.</p>
<h5><code>readableStreamDefaultController.desiredSize</code><span><a class="mark" href="#readablestreamdefaultcontrollerdesiredsize" id="readablestreamdefaultcontrollerdesiredsize">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestreamdefaultcontroller_desiredsize"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
</ul>
<p>Returns the amount of data remaining to fill the <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a>'s
queue.</p>
<h5><code>readableStreamDefaultController.enqueue(chunk)</code><span><a class="mark" href="#readablestreamdefaultcontrollerenqueuechunk" id="readablestreamdefaultcontrollerenqueuechunk">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestreamdefaultcontroller_enqueue_chunk"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>chunk</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
</ul>
<p>Appends a new chunk of data to the <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a>'s queue.</p>
<h5><code>readableStreamDefaultController.error(error)</code><span><a class="mark" href="#readablestreamdefaultcontrollererrorerror" id="readablestreamdefaultcontrollererrorerror">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestreamdefaultcontroller_error_error"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
</ul>
<p>Signals an error that causes the <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> to error and close.</p>
<h4>Class: <code>ReadableByteStreamController</code><span><a class="mark" href="#class-readablebytestreamcontroller" id="class-readablebytestreamcontroller">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_class_readablebytestreamcontroller"></a></h4>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<p>Every <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> has a controller that is responsible for
the internal state and management of the stream's queue. The
<code>ReadableByteStreamController</code> is for byte-oriented <code>ReadableStream</code>s.</p>
<h5><code>readableByteStreamController.byobRequest</code><span><a class="mark" href="#readablebytestreamcontrollerbyobrequest" id="readablebytestreamcontrollerbyobrequest">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablebytestreamcontroller_byobrequest"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="webstreams.html#class-readablestreambyobrequest" class="type"><ReadableStreamBYOBRequest></a></li>
</ul>
<h5><code>readableByteStreamController.close()</code><span><a class="mark" href="#readablebytestreamcontrollerclose" id="readablebytestreamcontrollerclose">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablebytestreamcontroller_close"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<p>Closes the <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> to which this controller is associated.</p>
<h5><code>readableByteStreamController.desiredSize</code><span><a class="mark" href="#readablebytestreamcontrollerdesiredsize" id="readablebytestreamcontrollerdesiredsize">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablebytestreamcontroller_desiredsize"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
</ul>
<p>Returns the amount of data remaining to fill the <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a>'s
queue.</p>
<h5><code>readableByteStreamController.enqueue(chunk)</code><span><a class="mark" href="#readablebytestreamcontrollerenqueuechunk" id="readablebytestreamcontrollerenqueuechunk">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablebytestreamcontroller_enqueue_chunk"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>chunk</code>: <a href="buffer.html#class-buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray" class="type"><TypedArray></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView" class="type"><DataView></a></li>
</ul>
<p>Appends a new chunk of data to the <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a>'s queue.</p>
<h5><code>readableByteStreamController.error(error)</code><span><a class="mark" href="#readablebytestreamcontrollererrorerror" id="readablebytestreamcontrollererrorerror">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablebytestreamcontroller_error_error"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
</ul>
<p>Signals an error that causes the <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> to error and close.</p>
<h4>Class: <code>ReadableStreamBYOBRequest</code><span><a class="mark" href="#class-readablestreambyobrequest" id="class-readablestreambyobrequest">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_class_readablestreambyobrequest"></a></h4>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<p>When using <code>ReadableByteStreamController</code> in byte-oriented
streams, and when using the <code>ReadableStreamBYOBReader</code>,
the <code>readableByteStreamController.byobRequest</code> property
provides access to a <code>ReadableStreamBYOBRequest</code> instance
that represents the current read request. The object
is used to gain access to the <code>ArrayBuffer</code>/<code>TypedArray</code>
that has been provided for the read request to fill,
and provides methods for signaling that the data has
been provided.</p>
<h5><code>readableStreamBYOBRequest.respond(bytesWritten)</code><span><a class="mark" href="#readablestreambyobrequestrespondbyteswritten" id="readablestreambyobrequestrespondbyteswritten">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestreambyobrequest_respond_byteswritten"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>bytesWritten</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
</ul>
<p>Signals that a <code>bytesWritten</code> number of bytes have been written
to <code>readableStreamBYOBRequest.view</code>.</p>
<h5><code>readableStreamBYOBRequest.respondWithNewView(view)</code><span><a class="mark" href="#readablestreambyobrequestrespondwithnewviewview" id="readablestreambyobrequestrespondwithnewviewview">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestreambyobrequest_respondwithnewview_view"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>view</code> <a href="buffer.html#class-buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray" class="type"><TypedArray></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView" class="type"><DataView></a></li>
</ul>
<p>Signals that the request has been fulfilled with bytes written
to a new <code>Buffer</code>, <code>TypedArray</code>, or <code>DataView</code>.</p>
<h5><code>readableStreamBYOBRequest.view</code><span><a class="mark" href="#readablestreambyobrequestview" id="readablestreambyobrequestview">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_readablestreambyobrequest_view"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="buffer.html#class-buffer" class="type"><Buffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray" class="type"><TypedArray></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView" class="type"><DataView></a></li>
</ul>
<h4>Class: <code>WritableStream</code><span><a class="mark" href="#class-writablestream" id="class-writablestream">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_class_writablestream"></a></h4>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<p>The <code>WritableStream</code> is a destination to which stream data is sent.</p>
<pre><code class="language-js mjs"><span class="hljs-keyword">import</span> {
<span class="hljs-title class_">WritableStream</span>
} <span class="hljs-keyword">from</span> <span class="hljs-string">'node:stream/web'</span>;
<span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WritableStream</span>({
<span class="hljs-title function_">write</span>(<span class="hljs-params">chunk</span>) {
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(chunk);
}
});
<span class="hljs-keyword">await</span> stream.<span class="hljs-title function_">getWriter</span>().<span class="hljs-title function_">write</span>(<span class="hljs-string">'Hello World'</span>);</code></pre>
<h5><code>new WritableStream([underlyingSink[, strategy]])</code><span><a class="mark" href="#new-writablestreamunderlyingsink-strategy" id="new-writablestreamunderlyingsink-strategy">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_new_writablestream_underlyingsink_strategy"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>underlyingSink</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>start</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A user-defined function that is invoked immediately when
the <code>WritableStream</code> is created.
<ul>
<li><code>controller</code> <a href="webstreams.html#class-writablestreamdefaultcontroller" class="type"><WritableStreamDefaultController></a></li>
<li>Returns: <code>undefined</code> or a promise fulfilled with <code>undefined</code>.</li>
</ul>
</li>
<li><code>write</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A user-defined function that is invoked when a chunk of
data has been written to the <code>WritableStream</code>.
<ul>
<li><code>chunk</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>controller</code> <a href="webstreams.html#class-writablestreamdefaultcontroller" class="type"><WritableStreamDefaultController></a></li>
<li>Returns: A promise fulfilled with <code>undefined</code>.</li>
</ul>
</li>
<li><code>close</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A user-defined function that is called when the
<code>WritableStream</code> is closed.
<ul>
<li>Returns: A promise fulfilled with <code>undefined</code>.</li>
</ul>
</li>
<li><code>abort</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A user-defined function that is called to abruptly close
the <code>WritableStream</code>.
<ul>
<li><code>reason</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: A promise fulfilled with <code>undefined</code>.</li>
</ul>
</li>
<li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> The <code>type</code> option is reserved for future use and <em>must</em> be
undefined.</li>
</ul>
</li>
<li><code>strategy</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>highWaterMark</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The maximum internal queue size before backpressure
is applied.</li>
<li><code>size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A user-defined function used to identify the size of each
chunk of data.
<ul>
<li><code>chunk</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
</ul>
</li>
</ul>
</li>
</ul>
<h5><code>writableStream.abort([reason])</code><span><a class="mark" href="#writablestreamabortreason" id="writablestreamabortreason">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_writablestream_abort_reason"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>reason</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: A promise fulfilled with <code>undefined</code>.</li>
</ul>
<p>Abruptly terminates the <code>WritableStream</code>. All queued writes will be
canceled with their associated promises rejected.</p>
<h5><code>writableStream.close()</code><span><a class="mark" href="#writablestreamclose" id="writablestreamclose">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_writablestream_close"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Returns: A promise fulfilled with <code>undefined</code>.</li>
</ul>
<p>Closes the <code>WritableStream</code> when no additional writes are expected.</p>
<h5><code>writableStream.getWriter()</code><span><a class="mark" href="#writablestreamgetwriter" id="writablestreamgetwriter">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_writablestream_getwriter"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Returns: <a href="webstreams.html#class-writablestreamdefaultwriter" class="type"><WritableStreamDefaultWriter></a></li>
</ul>
<p>Creates and creates a new writer instance that can be used to write
data into the <code>WritableStream</code>.</p>
<h5><code>writableStream.locked</code><span><a class="mark" href="#writablestreamlocked" id="writablestreamlocked">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_writablestream_locked"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>The <code>writableStream.locked</code> property is <code>false</code> by default, and is
switched to <code>true</code> while there is an active writer attached to this
<code>WritableStream</code>.</p>
<h5>Transferring with postMessage()<span><a class="mark" href="#transferring-with-postmessage_1" id="transferring-with-postmessage_1">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_transferring_with_postmessage_1"></a></h5>
<p>A <a href="webstreams.html#class-writablestream" class="type"><WritableStream></a> instance can be transferred using a <a href="worker_threads.html#class-messageport" class="type"><MessagePort></a>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WritableStream</span>(<span class="hljs-title function_">getWritableSinkSomehow</span>());
<span class="hljs-keyword">const</span> { port1, port2 } = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MessageChannel</span>();
port1.<span class="hljs-property">onmessage</span> = <span class="hljs-function">(<span class="hljs-params">{ data }</span>) =></span> {
data.<span class="hljs-title function_">getWriter</span>().<span class="hljs-title function_">write</span>(<span class="hljs-string">'hello'</span>);
};
port2.<span class="hljs-title function_">postMessage</span>(stream, [stream]);</code></pre>
<h4>Class: <code>WritableStreamDefaultWriter</code><span><a class="mark" href="#class-writablestreamdefaultwriter" id="class-writablestreamdefaultwriter">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_class_writablestreamdefaultwriter"></a></h4>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<h5><code>new WritableStreamDefaultWriter(stream)</code><span><a class="mark" href="#new-writablestreamdefaultwriterstream" id="new-writablestreamdefaultwriterstream">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_new_writablestreamdefaultwriter_stream"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>stream</code> <a href="webstreams.html#class-writablestream" class="type"><WritableStream></a></li>
</ul>
<p>Creates a new <code>WritableStreamDefaultWriter</code> that is locked to the given
<code>WritableStream</code>.</p>
<h5><code>writableStreamDefaultWriter.abort([reason])</code><span><a class="mark" href="#writablestreamdefaultwriterabortreason" id="writablestreamdefaultwriterabortreason">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_writablestreamdefaultwriter_abort_reason"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>reason</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: A promise fulfilled with <code>undefined</code>.</li>
</ul>
<p>Abruptly terminates the <code>WritableStream</code>. All queued writes will be
canceled with their associated promises rejected.</p>
<h5><code>writableStreamDefaultWriter.close()</code><span><a class="mark" href="#writablestreamdefaultwriterclose" id="writablestreamdefaultwriterclose">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_writablestreamdefaultwriter_close"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Returns: A promise fulfilled with <code>undefined</code>.</li>
</ul>
<p>Closes the <code>WritableStream</code> when no additional writes are expected.</p>
<h5><code>writableStreamDefaultWriter.closed</code><span><a class="mark" href="#writablestreamdefaultwriterclosed" id="writablestreamdefaultwriterclosed">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_writablestreamdefaultwriter_closed"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a> Fulfilled with <code>undefined</code> when the associated
<a href="webstreams.html#class-writablestream" class="type"><WritableStream></a> is closed or rejected if the stream errors or the writer's
lock is released before the stream finishes closing.</li>
</ul>
<h5><code>writableStreamDefaultWriter.desiredSize</code><span><a class="mark" href="#writablestreamdefaultwriterdesiredsize" id="writablestreamdefaultwriterdesiredsize">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_writablestreamdefaultwriter_desiredsize"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
</ul>
<p>The amount of data required to fill the <a href="webstreams.html#class-writablestream" class="type"><WritableStream></a>'s queue.</p>
<h5><code>writableStreamDefaultWriter.ready</code><span><a class="mark" href="#writablestreamdefaultwriterready" id="writablestreamdefaultwriterready">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_writablestreamdefaultwriter_ready"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>type: A promise that is fulfilled with <code>undefined</code> when the
writer is ready to be used.</li>
</ul>
<h5><code>writableStreamDefaultWriter.releaseLock()</code><span><a class="mark" href="#writablestreamdefaultwriterreleaselock" id="writablestreamdefaultwriterreleaselock">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_writablestreamdefaultwriter_releaselock"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<p>Releases this writer's lock on the underlying <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a>.</p>
<h5><code>writableStreamDefaultWriter.write([chunk])</code><span><a class="mark" href="#writablestreamdefaultwriterwritechunk" id="writablestreamdefaultwriterwritechunk">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_writablestreamdefaultwriter_write_chunk"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>chunk</code>: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: A promise fulfilled with <code>undefined</code>.</li>
</ul>
<p>Appends a new chunk of data to the <a href="webstreams.html#class-writablestream" class="type"><WritableStream></a>'s queue.</p>
<h4>Class: <code>WritableStreamDefaultController</code><span><a class="mark" href="#class-writablestreamdefaultcontroller" id="class-writablestreamdefaultcontroller">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_class_writablestreamdefaultcontroller"></a></h4>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<p>The <code>WritableStreamDefaultController</code> manage's the <a href="webstreams.html#class-writablestream" class="type"><WritableStream></a>'s
internal state.</p>
<h5><code>writableStreamDefaultController.abortReason</code><span><a class="mark" href="#writablestreamdefaultcontrollerabortreason" id="writablestreamdefaultcontrollerabortreason">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_writablestreamdefaultcontroller_abortreason"></a></h5>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> The <code>reason</code> value passed to <code>writableStream.abort()</code>.</li>
</ul>
<h5><code>writableStreamDefaultController.error(error)</code><span><a class="mark" href="#writablestreamdefaultcontrollererrorerror" id="writablestreamdefaultcontrollererrorerror">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_writablestreamdefaultcontroller_error_error"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
</ul>
<p>Called by user-code to signal that an error has occurred while processing
the <code>WritableStream</code> data. When called, the <a href="webstreams.html#class-writablestream" class="type"><WritableStream></a> will be aborted,
with currently pending writes canceled.</p>
<h5><code>writableStreamDefaultController.signal</code><span><a class="mark" href="#writablestreamdefaultcontrollersignal" id="writablestreamdefaultcontrollersignal">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_writablestreamdefaultcontroller_signal"></a></h5>
<ul>
<li>Type: <a href="globals.html#class-abortsignal" class="type"><AbortSignal></a> An <code>AbortSignal</code> that can be used to cancel pending
write or close operations when a <a href="webstreams.html#class-writablestream" class="type"><WritableStream></a> is aborted.</li>
</ul>
<h4>Class: <code>TransformStream</code><span><a class="mark" href="#class-transformstream" id="class-transformstream">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_class_transformstream"></a></h4>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<p>A <code>TransformStream</code> consists of a <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> and a <a href="webstreams.html#class-writablestream" class="type"><WritableStream></a> that
are connected such that the data written to the <code>WritableStream</code> is received,
and potentially transformed, before being pushed into the <code>ReadableStream</code>'s
queue.</p>
<pre><code class="language-js mjs"><span class="hljs-keyword">import</span> {
<span class="hljs-title class_">TransformStream</span>
} <span class="hljs-keyword">from</span> <span class="hljs-string">'node:stream/web'</span>;
<span class="hljs-keyword">const</span> transform = <span class="hljs-keyword">new</span> <span class="hljs-title class_">TransformStream</span>({
<span class="hljs-title function_">transform</span>(<span class="hljs-params">chunk, controller</span>) {
controller.<span class="hljs-title function_">enqueue</span>(chunk.<span class="hljs-title function_">toUpperCase</span>());
}
});
<span class="hljs-keyword">await</span> <span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">all</span>([
transform.<span class="hljs-property">writable</span>.<span class="hljs-title function_">getWriter</span>().<span class="hljs-title function_">write</span>(<span class="hljs-string">'A'</span>),
transform.<span class="hljs-property">readable</span>.<span class="hljs-title function_">getReader</span>().<span class="hljs-title function_">read</span>(),
]);</code></pre>
<h5><code>new TransformStream([transformer[, writableStrategy[, readableStrategy]]])</code><span><a class="mark" href="#new-transformstreamtransformer-writablestrategy-readablestrategy" id="new-transformstreamtransformer-writablestrategy-readablestrategy">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_new_transformstream_transformer_writablestrategy_readablestrategy"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>transformer</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>start</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A user-defined function that is invoked immediately when
the <code>TransformStream</code> is created.
<ul>
<li><code>controller</code> <a href="webstreams.html#class-transformstreamdefaultcontroller" class="type"><TransformStreamDefaultController></a></li>
<li>Returns: <code>undefined</code> or a promise fulfilled with <code>undefined</code></li>
</ul>
</li>
<li><code>transform</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A user-defined function that receives, and
potentially modifies, a chunk of data written to <code>transformStream.writable</code>,
before forwarding that on to <code>transformStream.readable</code>.
<ul>
<li><code>chunk</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>controller</code> <a href="webstreams.html#class-transformstreamdefaultcontroller" class="type"><TransformStreamDefaultController></a></li>
<li>Returns: A promise fulfilled with <code>undefined</code>.</li>
</ul>
</li>
<li><code>flush</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A user-defined function that is called immediately before
the writable side of the <code>TransformStream</code> is closed, signaling the end of
the transformation process.
<ul>
<li><code>controller</code> <a href="webstreams.html#class-transformstreamdefaultcontroller" class="type"><TransformStreamDefaultController></a></li>
<li>Returns: A promise fulfilled with <code>undefined</code>.</li>
</ul>
</li>
<li><code>readableType</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> the <code>readableType</code> option is reserved for future use
and <em>must</em> be <code>undefined</code>.</li>
<li><code>writableType</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> the <code>writableType</code> option is reserved for future use
and <em>must</em> be <code>undefined</code>.</li>
</ul>
</li>
<li><code>writableStrategy</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>highWaterMark</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The maximum internal queue size before backpressure
is applied.</li>
<li><code>size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A user-defined function used to identify the size of each
chunk of data.
<ul>
<li><code>chunk</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
</ul>
</li>
</ul>
</li>
<li><code>readableStrategy</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>highWaterMark</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The maximum internal queue size before backpressure
is applied.</li>
<li><code>size</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A user-defined function used to identify the size of each
chunk of data.
<ul>
<li><code>chunk</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
</ul>
</li>
</ul>
</li>
</ul>
<h5><code>transformStream.readable</code><span><a class="mark" href="#transformstreamreadable" id="transformstreamreadable">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_transformstream_readable"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a></li>
</ul>
<h5><code>transformStream.writable</code><span><a class="mark" href="#transformstreamwritable" id="transformstreamwritable">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_transformstream_writable"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="webstreams.html#class-writablestream" class="type"><WritableStream></a></li>
</ul>
<h5>Transferring with postMessage()<span><a class="mark" href="#transferring-with-postmessage_2" id="transferring-with-postmessage_2">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_transferring_with_postmessage_2"></a></h5>
<p>A <a href="webstreams.html#class-transformstream" class="type"><TransformStream></a> instance can be transferred using a <a href="worker_threads.html#class-messageport" class="type"><MessagePort></a>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">TransformStream</span>();
<span class="hljs-keyword">const</span> { port1, port2 } = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MessageChannel</span>();
port1.<span class="hljs-property">onmessage</span> = <span class="hljs-function">(<span class="hljs-params">{ data }</span>) =></span> {
<span class="hljs-keyword">const</span> { writable, readable } = data;
<span class="hljs-comment">// ...</span>
};
port2.<span class="hljs-title function_">postMessage</span>(stream, [stream]);</code></pre>
<h4>Class: <code>TransformStreamDefaultController</code><span><a class="mark" href="#class-transformstreamdefaultcontroller" id="class-transformstreamdefaultcontroller">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_class_transformstreamdefaultcontroller"></a></h4>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<p>The <code>TransformStreamDefaultController</code> manages the internal state
of the <code>TransformStream</code>.</p>
<h5><code>transformStreamDefaultController.desiredSize</code><span><a class="mark" href="#transformstreamdefaultcontrollerdesiredsize" id="transformstreamdefaultcontrollerdesiredsize">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_transformstreamdefaultcontroller_desiredsize"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
</ul>
<p>The amount of data required to fill the readable side's queue.</p>
<h5><code>transformStreamDefaultController.enqueue([chunk])</code><span><a class="mark" href="#transformstreamdefaultcontrollerenqueuechunk" id="transformstreamdefaultcontrollerenqueuechunk">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_transformstreamdefaultcontroller_enqueue_chunk"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>chunk</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
</ul>
<p>Appends a chunk of data to the readable side's queue.</p>
<h5><code>transformStreamDefaultController.error([reason])</code><span><a class="mark" href="#transformstreamdefaultcontrollererrorreason" id="transformstreamdefaultcontrollererrorreason">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_transformstreamdefaultcontroller_error_reason"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>reason</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
</ul>
<p>Signals to both the readable and writable side that an error has occurred
while processing the transform data, causing both sides to be abruptly
closed.</p>
<h5><code>transformStreamDefaultController.terminate()</code><span><a class="mark" href="#transformstreamdefaultcontrollerterminate" id="transformstreamdefaultcontrollerterminate">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_transformstreamdefaultcontroller_terminate"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<p>Closes the readable side of the transport and causes the writable side
to be abruptly closed with an error.</p>
<h4>Class: <code>ByteLengthQueuingStrategy</code><span><a class="mark" href="#class-bytelengthqueuingstrategy" id="class-bytelengthqueuingstrategy">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_class_bytelengthqueuingstrategy"></a></h4>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<h5><code>new ByteLengthQueuingStrategy(options)</code><span><a class="mark" href="#new-bytelengthqueuingstrategyoptions" id="new-bytelengthqueuingstrategyoptions">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_new_bytelengthqueuingstrategy_options"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>highWaterMark</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
</ul>
</li>
</ul>
<h5><code>byteLengthQueuingStrategy.highWaterMark</code><span><a class="mark" href="#bytelengthqueuingstrategyhighwatermark" id="bytelengthqueuingstrategyhighwatermark">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_bytelengthqueuingstrategy_highwatermark"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
</ul>
<h5><code>byteLengthQueuingStrategy.size</code><span><a class="mark" href="#bytelengthqueuingstrategysize" id="bytelengthqueuingstrategysize">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_bytelengthqueuingstrategy_size"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a>
<ul>
<li><code>chunk</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
</ul>
</li>
</ul>
<h4>Class: <code>CountQueuingStrategy</code><span><a class="mark" href="#class-countqueuingstrategy" id="class-countqueuingstrategy">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_class_countqueuingstrategy"></a></h4>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<h5><code>new CountQueuingStrategy(options)</code><span><a class="mark" href="#new-countqueuingstrategyoptions" id="new-countqueuingstrategyoptions">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_new_countqueuingstrategy_options"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>highWaterMark</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
</ul>
</li>
</ul>
<h5><code>countQueuingStrategy.highWaterMark</code><span><a class="mark" href="#countqueuingstrategyhighwatermark" id="countqueuingstrategyhighwatermark">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_countqueuingstrategy_highwatermark"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
</ul>
<h5><code>countQueuingStrategy.size</code><span><a class="mark" href="#countqueuingstrategysize" id="countqueuingstrategysize">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_countqueuingstrategy_size"></a></h5>
<div class="api_metadata">
<span>Added in: v16.5.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a>
<ul>
<li><code>chunk</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
</ul>
</li>
</ul>
<h4>Class: <code>TextEncoderStream</code><span><a class="mark" href="#class-textencoderstream" id="class-textencoderstream">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_class_textencoderstream"></a></h4>
<div class="api_metadata">
<span>Added in: v16.6.0</span>
</div>
<h5><code>new TextEncoderStream()</code><span><a class="mark" href="#new-textencoderstream" id="new-textencoderstream">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_new_textencoderstream"></a></h5>
<div class="api_metadata">
<span>Added in: v16.6.0</span>
</div>
<p>Creates a new <code>TextEncoderStream</code> instance.</p>
<h5><code>textEncoderStream.encoding</code><span><a class="mark" href="#textencoderstreamencoding" id="textencoderstreamencoding">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_textencoderstream_encoding"></a></h5>
<div class="api_metadata">
<span>Added in: v16.6.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>The encoding supported by the <code>TextEncoderStream</code> instance.</p>
<h5><code>textEncoderStream.readable</code><span><a class="mark" href="#textencoderstreamreadable" id="textencoderstreamreadable">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_textencoderstream_readable"></a></h5>
<div class="api_metadata">
<span>Added in: v16.6.0</span>
</div>
<ul>
<li>Type: <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a></li>
</ul>
<h5><code>textEncoderStream.writable</code><span><a class="mark" href="#textencoderstreamwritable" id="textencoderstreamwritable">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_textencoderstream_writable"></a></h5>
<div class="api_metadata">
<span>Added in: v16.6.0</span>
</div>
<ul>
<li>Type: <a href="webstreams.html#class-writablestream" class="type"><WritableStream></a></li>
</ul>
<h4>Class: <code>TextDecoderStream</code><span><a class="mark" href="#class-textdecoderstream" id="class-textdecoderstream">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_class_textdecoderstream"></a></h4>
<div class="api_metadata">
<span>Added in: v16.6.0</span>
</div>
<h5><code>new TextDecoderStream([encoding[, options]])</code><span><a class="mark" href="#new-textdecoderstreamencoding-options" id="new-textdecoderstreamencoding-options">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_new_textdecoderstream_encoding_options"></a></h5>
<div class="api_metadata">
<span>Added in: v16.6.0</span>
</div>
<ul>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Identifies the <code>encoding</code> that this <code>TextDecoder</code> instance
supports. <strong>Default:</strong> <code>'utf-8'</code>.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>fatal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> if decoding failures are fatal.</li>
<li><code>ignoreBOM</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> When <code>true</code>, the <code>TextDecoderStream</code> will include the
byte order mark in the decoded result. When <code>false</code>, the byte order mark
will be removed from the output. This option is only used when <code>encoding</code> is
<code>'utf-8'</code>, <code>'utf-16be'</code> or <code>'utf-16le'</code>. <strong>Default:</strong> <code>false</code>.</li>
</ul>
</li>
</ul>
<p>Creates a new <code>TextDecoderStream</code> instance.</p>
<h5><code>textDecoderStream.encoding</code><span><a class="mark" href="#textdecoderstreamencoding" id="textdecoderstreamencoding">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_textdecoderstream_encoding"></a></h5>
<div class="api_metadata">
<span>Added in: v16.6.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>The encoding supported by the <code>TextDecoderStream</code> instance.</p>
<h5><code>textDecoderStream.fatal</code><span><a class="mark" href="#textdecoderstreamfatal" id="textdecoderstreamfatal">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_textdecoderstream_fatal"></a></h5>
<div class="api_metadata">
<span>Added in: v16.6.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>The value will be <code>true</code> if decoding errors result in a <code>TypeError</code> being
thrown.</p>
<h5><code>textDecoderStream.ignoreBOM</code><span><a class="mark" href="#textdecoderstreamignorebom" id="textdecoderstreamignorebom">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_textdecoderstream_ignorebom"></a></h5>
<div class="api_metadata">
<span>Added in: v16.6.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>The value will be <code>true</code> if the decoding result will include the byte order
mark.</p>
<h5><code>textDecoderStream.readable</code><span><a class="mark" href="#textdecoderstreamreadable" id="textdecoderstreamreadable">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_textdecoderstream_readable"></a></h5>
<div class="api_metadata">
<span>Added in: v16.6.0</span>
</div>
<ul>
<li>Type: <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a></li>
</ul>
<h5><code>textDecoderStream.writable</code><span><a class="mark" href="#textdecoderstreamwritable" id="textdecoderstreamwritable">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_textdecoderstream_writable"></a></h5>
<div class="api_metadata">
<span>Added in: v16.6.0</span>
</div>
<ul>
<li>Type: <a href="webstreams.html#class-writablestream" class="type"><WritableStream></a></li>
</ul>
<h4>Utility Consumers<span><a class="mark" href="#utility-consumers" id="utility-consumers">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_utility_consumers"></a></h4>
<div class="api_metadata">
<span>Added in: v16.7.0</span>
</div>
<p>The utility consumer functions provide common options for consuming
streams.</p>
<p>They are accessed using:</p>
<pre><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> {
arrayBuffer,
blob,
buffer,
json,
text,
} <span class="hljs-keyword">from</span> <span class="hljs-string">'node:stream/consumers'</span>;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> {
arrayBuffer,
blob,
buffer,
json,
text,
} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'stream/consumers'</span>);</code></pre>
<h5><code>streamConsumers.arrayBuffer(stream)</code><span><a class="mark" href="#streamconsumersarraybufferstream" id="streamconsumersarraybufferstream">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_streamconsumers_arraybuffer_stream"></a></h5>
<div class="api_metadata">
<span>Added in: v16.7.0</span>
</div>
<ul>
<li><code>stream</code> <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> | <a href="stream.html#class-streamreadable" class="type"><stream.Readable></a> | <a href="https://tc39.github.io/ecma262/#sec-asynciterator-interface" class="type"><AsyncIterator></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a> Fulfills with an <code>ArrayBuffer</code> containing the full
contents of the stream.</li>
</ul>
<h5><code>streamConsumers.blob(stream)</code><span><a class="mark" href="#streamconsumersblobstream" id="streamconsumersblobstream">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_streamconsumers_blob_stream"></a></h5>
<div class="api_metadata">
<span>Added in: v16.7.0</span>
</div>
<ul>
<li><code>stream</code> <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> | <a href="stream.html#class-streamreadable" class="type"><stream.Readable></a> | <a href="https://tc39.github.io/ecma262/#sec-asynciterator-interface" class="type"><AsyncIterator></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a> Fulfills with a <a href="buffer.html#class-blob" class="type"><Blob></a> containing the full contents
of the stream.</li>
</ul>
<h5><code>streamConsumers.buffer(stream)</code><span><a class="mark" href="#streamconsumersbufferstream" id="streamconsumersbufferstream">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_streamconsumers_buffer_stream"></a></h5>
<div class="api_metadata">
<span>Added in: v16.7.0</span>
</div>
<ul>
<li><code>stream</code> <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> | <a href="stream.html#class-streamreadable" class="type"><stream.Readable></a> | <a href="https://tc39.github.io/ecma262/#sec-asynciterator-interface" class="type"><AsyncIterator></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a> Fulfills with a <a href="buffer.html#class-buffer" class="type"><Buffer></a> containing the full
contents of the stream.</li>
</ul>
<h5><code>streamConsumers.json(stream)</code><span><a class="mark" href="#streamconsumersjsonstream" id="streamconsumersjsonstream">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_streamconsumers_json_stream"></a></h5>
<div class="api_metadata">
<span>Added in: v16.7.0</span>
</div>
<ul>
<li><code>stream</code> <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> | <a href="stream.html#class-streamreadable" class="type"><stream.Readable></a> | <a href="https://tc39.github.io/ecma262/#sec-asynciterator-interface" class="type"><AsyncIterator></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a> Fulfills with the contents of the stream parsed as a
UTF-8 encoded string that is then passed through <code>JSON.parse()</code>.</li>
</ul>
<h5><code>streamConsumers.text(stream)</code><span><a class="mark" href="#streamconsumerstextstream" id="streamconsumerstextstream">#</a></span><a aria-hidden="true" class="legacy" id="webstreams_streamconsumers_text_stream"></a></h5>
<div class="api_metadata">
<span>Added in: v16.7.0</span>
</div>
<ul>
<li><code>stream</code> <a href="webstreams.html#class-readablestream" class="type"><ReadableStream></a> | <a href="stream.html#class-streamreadable" class="type"><stream.Readable></a> | <a href="https://tc39.github.io/ecma262/#sec-asynciterator-interface" class="type"><AsyncIterator></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a> Fulfills with the contents of the stream parsed as a
UTF-8 encoded string.</li>
</ul></section>
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