This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The write()
property of the WritableStreamDefaultWriter
interface writes a passed chunk of data to a WritableStream
and its underlying sink, then returns a Promise
that resolves to indicate the success or failure of the write operation.
Note that what "success" means is up to the underlying sink; it might indicate simply that the chunk has been accepted, and not necessarily that it is safely saved to its ultimate destination.
Syntax
var promise = writableStreamDefaultWriter.write(chunk);
Parameters
- chunk
- A block of binary data to pass to the
WritableStream
.
Return value
A Promise
, which fulfills with the undefined
upon a successful write, or rejects if the write fails or stream becomes errored before the writing process is initiated.
Exceptions
- TypeError
- The target stream is not a writable stream, or it does not have an owner.
Examples
The following example shows the creation of a 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.
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(() => { return 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) => { var buffer = new ArrayBuffer(2); var view = new Uint16Array(buffer); view[0] = chunk; var decoded = decoder.decode(view, { stream: true }); var listItem = document.createElement('li'); listItem.textContent = "Chunk decoded: " + decoded; list.appendChild(listItem); result += decoded; resolve(); }); }, close() { var 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.
Specifications
Specification | Status | Comment |
---|---|---|
Streams The definition of 'write()' in that specification. |
Living Standard | Initial definition. |
Browser compatibility
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
write | Chrome Full support 59 | Edge Full support 16 | Firefox No support No | IE No support No | Opera Full support 46 | Safari ? | WebView Android Full support 59 | Chrome Android Full support 59 | Firefox Android No support No | Opera Android Full support 43 | Safari iOS ? | Samsung Internet Android Full support 7.0 |
Legend
- Full support
- Full support
- No support
- No support
- Compatibility unknown
- Compatibility unknown
- Experimental. Expect behavior to change in the future.
- Experimental. Expect behavior to change in the future.