files/en-us/web/api/readablestreamdefaultcontroller/enqueue/index.md
{{APIRef("Streams")}}{{AvailableInWorkers}}
The enqueue() method of the
{{domxref("ReadableStreamDefaultController")}} interface enqueues a given chunk in the associated stream.
enqueue(chunk)
chunk
None ({{jsxref("undefined")}}).
enqueue() is called when the stream is not readable — because it is already closed, cancelled, or errored — or because it has been requested to close by the underlying source but it has not yet done so because there are still enqueued chunks to read.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 — see
controller.enqueue(string). A cancel() function is also
provided to stop the generation if {{domxref("ReadableStream.cancel()")}} is called for
any reason.
When a button is pressed, the generation is stopped, the stream is closed using {{domxref("ReadableStreamDefaultController.close()")}}, and another function is run, which reads the data back out of the stream.
let interval;
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", () => {
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}}
{{Compat}}