ReadableStreamDefaultController: enqueue() method

Note: This feature is available in Web Workers.

The enqueue() method of the ReadableStreamDefaultController interface enqueues a given chunk in the associated stream.

Syntax

js
enqueue(chunk)

Parameters

chunk

The chunk to enqueue.

Return value

None (undefined).

Exceptions

TypeError

Thrown if the source object is not a ReadableStreamDefaultController.

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 — see controller.enqueue(string). A cancel() function is also provided to stop the generation if ReadableStream.cancel() is called for any reason.

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.

js
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

Specification
Streams Standard
# ref-for-rs-default-controller-enqueue①

Browser compatibility

BCD tables only load in the browser

See also