This is an experimental technologyCheck 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 [[../../../../../../../mdn.github.io/dom-examples/streams/simple-writer/index|Simple writer example]].
Specifications
Specification | Status | Comment |
StreamsThe definition of 'write()' in that specification. | Living Standard | Initial definition. |
Browser compatibility
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Update compatibility data on GitHub
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
|
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.
WritableStreamDefaultWriter.write() by Mozilla Contributors is licensed under CC-BY-SA 2.5.