ReadableStreamDefaultController
The ReadableStreamDefaultController
interface of the Streams API represents a controller allowing control of a ReadableStream
's state and internal queue. Default controllers are for streams that are not byte streams.
Constructor
None. ReadableStreamDefaultController
instances are created automatically during ReadableStream
construction.
Properties
ReadableStreamDefaultController.desiredSize
Read only-
Returns the desired size required to fill the stream's internal queue.
Methods
ReadableStreamDefaultController.close()
-
Closes the associated stream.
ReadableStreamDefaultController.enqueue()
-
Enqueues a given chunk in the associated stream.
ReadableStreamDefaultController.error()
-
Causes any future interactions with the associated stream to error.
Examples
In the following simple example, a custom ReadableStream
is created using a constructor (see our Simple random stream example for the full code). The start()
function generates a random string of text every second and enqueues it into the stream. A cancel()
function is also provided to stop the generation if ReadableStream.cancel()
is called for any reason.
Note that a ReadableStreamDefaultController
object is provided as the parameter of the start()
and pull()
functions.
When a button is pressed, the generation is stopped, the stream is closed using ReadableStreamDefaultController.close()
, and another function is run, which reads the data back out of the stream.
const stream = new ReadableStream({
start(controller) {
interval = setInterval(() => {
let string = randomChars();
// Add the string to the stream
controller.enqueue(string);
// show it on the screen
let listItem = document.createElement('li');
listItem.textContent = string;
list1.appendChild(listItem);
}, 1000);
button.addEventListener('click', function() {
clearInterval(interval);
fetchStream();
controller.close();
})
},
pull(controller) {
// We don't really need a pull in this example
},
cancel() {
// This is called if the reader cancels,
// so we should stop generating strings
clearInterval(interval);
}
});
Specifications
Specification |
---|
Streams Standard # rs-default-controller-class |
Browser compatibility
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