WritableStreamDefaultController: signal property
Note: This feature is available in Web Workers.
The read-only signal
property of the WritableStreamDefaultController
interface returns the AbortSignal
associated with the controller.
Value
An AbortSignal
object.
Examples
Aborting a long write operation
In this example, we simulate a slow operation using a local sink: We do nothing when some data is written but to wait for a second. This gives us enough time to call the writer.abort()
method and to immediately reject the promise.
js
const writingStream = new WritableStream({
// Define the slow local sink to simulate a long operation
write(chunk, controller) {
return new Promise((resolve, reject) => {
controller.signal.addEventListener("abort", () =>
reject(controller.signal.reason),
);
// Do nothing but wait with the data: it is a local sink
setTimeout(resolve, 1000); // Timeout to simulate a slow operation
});
},
});
// Perform the write
const writer = writingStream.getWriter();
writer.write("Lorem ipsum test data");
// Abort the write manually
await writer.abort("Manual abort!");
Transferring the AbortSignal
to the underlying layer
In this example, we use the Fetch API to actually send the message to a server. The Fetch API also support AbortSignal
: It is possible to use the same object for both the fetch
method and the WritableStreamDefaultController
.
js
const endpoint = "https://www.example.com/api"; // Fake URL for example purpose
const writingStream = new WritableStream({
async write(chunk, controller) {
// Write to the server using the Fetch API
const response = await fetch(endpoint, {
signal: controller.signal, // We use the same object for both fetch and controller
method: "POST",
body: chunk,
});
await response.text();
},
});
// Perform the write
const writer = writingStream.getWriter();
writer.write("Lorem ipsum test data");
// Abort the write manually
await writer.abort("Manual abort!");
Specifications
Specification |
---|
Streams Standard # ref-for-ws-default-controller-signal① |
Browser compatibility
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