ReadableStreamDefaultController

This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

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

ReadableStreamDefaultController()
Creates and returns a ReadableStreamDefaultController() object instance.

Properties

ReadableStreamDefaultController.desiredSize
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 Status Comment
Streams
The definition of 'ReadableStreamDefaultController' in that specification.
Living Standard Initial definition

Browser Compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support

52.0

No support[1] ?

39

?
Feature Android Webview Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support 52 52 No support[1] ? 39 ?

[1] Readable streams are currently enabled in Firefox, but hidden behind the dom.streams.enabled and javascript.options.streams prefs.

Document Tags and Contributors

 Contributors to this page: chrisdavidmills
 Last updated by: chrisdavidmills,