WritableStreamDefaultWriter: close() method - Web APIs | MDN

WritableStreamDefaultWriter: close() method - Web APIs | MDN
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WritableStreamDefaultWriter: close() method
Baseline
Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since May 2022.
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Note:
This feature is available in
Web Workers
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
js
close()
Parameters
None.
Return value
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
. Each chunk of the
encoded string is written to the stream using the
write()
method, and the
forEach()
method of the encoded
Uint8Array
to process it byte-by-byte.
Finally,
close()
is called and the Promise it returns is handled to deal
with success (or any failures) of the chunked write operations.
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);
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 view a live demonstration of this at our
simple writer example
Specifications
Specification
Streams
# ref-for-default-writer-close⑦
Browser compatibility
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This page was last modified on
Apr 22, 2024
by
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