This is an experimental technologyCheck the Browser compatibility table carefully before using this in production.
The WritableStreamDefaultWriter
interface of the the Streams API is the object returned by WritableStream.getWriter()
and once created locks the writer to the WritableStream
ensuring that no other streams can write to the underlying sink.
Constructor
WritableStreamDefaultWriter()
- Creates a new
WritableStreamDefaultWriter
object instance.
Properties
WritableStreamDefaultWriter.closed
Read only- Allows you to write code that responds to an end to the streaming process. Returns a promise that fulfills if the stream becomes closed or the writer's lock is released, or rejects if the stream errors.
WritableStreamDefaultWriter.desiredSize
Read only- Returns the desired size required to fill the stream's internal queue.
WritableStreamDefaultWriter.ready
Read only- Returns a
Promise
that resolves when the desired size of the stream's internal queue transitions from non-positive to positive, signaling that it is no longer applying backpressure.
Methods
WritableStreamDefaultWriter.abort()
- Aborts the stream, signaling that the producer can no longer successfully write to the stream and it is to be immediately moved to an error state, with any queued writes discarded.
WritableStreamDefaultWriter.close()
- Closes the associated writable stream.
WritableStreamDefaultWriter.releaseLock()
- Releases the writer's lock on the corresponding stream. After the lock is released, the writer is no longer active. If the associated stream is errored when the lock is released, the writer will appear errored in the same way from now on; otherwise, the writer will appear closed.
WritableStreamDefaultWriter.write()
- Writes a passed chunk of data to a
WritableStream
and its underlying sink, then returns aPromise
that resolves to indicate the success or failure of the write operation.
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 'WritableStreamDefaultWriter' 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 |
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 | |
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 | |
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 | |
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 | |
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 | |
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 | |
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 | |
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 by Mozilla Contributors is licensed under CC-BY-SA 2.5.