The getWriter()
method of the WritableStream
interface returns a new instance of WritableStreamDefaultWriter
and locks the stream to that instance. While the stream is locked, no other writer can be acquired until this one is released.
The getWriter()
method of the WritableStream
interface returns a new instance of WritableStreamDefaultWriter
and locks the stream to that instance. While the stream is locked, no other writer can be acquired until this one is released.
js
getWriter()
None.
A WritableStreamDefaultWriter
object instance.
TypeError
The stream you are trying to create a writer for is not a WritableStream
.
The following example illustrates several features of this interface. It shows the creation of the WritableStream
with a custom sink and an API-supplied queuing strategy. It then calls a function called sendMessage()
, passing the newly created stream and a string. Inside this function it calls the stream's getWriter()
method, which returns an instance of WritableStreamDefaultWriter
. A forEach()
call is used to write each chunk of the string to the stream. Finally, write()
and close()
return promises that are processed to deal with success or failure of chunks and streams.
js
const list = document.querySelector("ul"); function sendMessage(message, writableStream) { // defaultWriter is of type WritableStreamDefaultWriter const defaultWriter = writableStream.getWriter(); const encoder = new TextEncoder(); const encoded = encoder.encode(message, { stream: true }); encoded.forEach((chunk) => { defaultWriter.ready .then(() => defaultWriter.write(chunk)) .then(() => { console.log("Chunk written to sink."); }) .catch((err) => { console.log("Chunk error:", err); }); }); // Call ready again to ensure that all chunks are written // before closing the writer. defaultWriter.ready .then(() => { defaultWriter.close(); }) .then(() => { console.log("All chunks written"); }) .catch((err) => { console.log("Stream error:", err); }); } const decoder = new TextDecoder("utf-8"); const queuingStrategy = new CountQueuingStrategy({ highWaterMark: 1 }); let result = ""; const writableStream = new WritableStream( { // Implement the sink write(chunk) { return new Promise((resolve, reject) => { const buffer = new ArrayBuffer(1); const view = new Uint8Array(buffer); view[0] = chunk; const decoded = decoder.decode(view, { stream: true }); const listItem = document.createElement("li"); listItem.textContent = `Chunk decoded: ${decoded}`; list.appendChild(listItem); result += decoded; resolve(); }); }, close() { const listItem = document.createElement("li"); listItem.textContent = `[MESSAGE RECEIVED] ${result}`; list.appendChild(listItem); }, abort(err) { console.log("Sink error:", err); }, }, queuingStrategy, ); sendMessage("Hello, world.", writableStream);
You can find the full code in our Simple writer example.
Specification |
---|
Streams Standard # ref-for-ws-get-writer① |
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
getWriter |
59 | 16 | 100 | No | 47 | 14.1 | 59 | 59 | 100 | 44 | 14.5 | 7.0 |
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https://developer.mozilla.org/en-US/docs/Web/API/WritableStream/getWriter