ReadableStreamDefaultController: close() method

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since January 2020.

Note: This feature is available in Web Workers.

The close() method of the ReadableStreamDefaultController interface closes the associated stream.

Readers will still be able to read any previously-enqueued chunks from the stream, but once those are read, the stream will become closed. If you want to completely get rid of the stream and discard any enqueued chunks, you'd use ReadableStream.cancel() or ReadableStreamDefaultReader.cancel().

Syntax

close()

Parameters

None.

Return value

None (undefined).

Exceptions

TypeError

Thrown if close() 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.

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.

When a button is pressed, the generation is stopped, the stream is closed using 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);
  },
});