WritableStreamDefaultWriter.close()
Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The close()
method of the
WritableStreamDefaultWriter
interface closes the associated writable
stream.
The underlying sink will finish processing any previously-written chunks, before invoking the close behavior. During this time any further attempts to write will fail (without erroring the stream).
Syntax
var promise = writableStreamDefaultWriter.close();
Parameters
None.
Return value
A Promise
, which fulfills with the undefined
if all
remaining chunks were successfully written before the close, or rejects with an error if
a problem was encountered during the process.
Exceptions
- TypeError
-
The stream you are trying to close is not a
WritableStream
.
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(1);
var view = new Uint8Array(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 |
---|
Streams Standard # ref-for-default-writer-close⑦ |
Browser compatibility
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