ReadableStreamBYOBReader

The ReadableStreamDefaultReader interface of the Streams API represents a BYOB ("bring your own buffer") reader that can be used to read stream data supplied by the developer (e.g. a custom ReadableStream.ReadableSteam() constructor).

Constructor

ReadableStreamBYOBReader()

Creates and returns a ReadableStreamBYOBReader() object instance.

Properties

ReadableStreamBYOBReader.closed

Allows you to write code that responds to an end to the streaming process. Returns a promise that fulfills if the stream becomes closed or the reader's lock is released, or rejects if the stream errors.

Methods

ReadableStreamBYOBReader.cancel()

Cancels the stream, signaling a loss of interest in the stream by a consumer. The supplied reason argument will be given to the underlying source, which may or may not use it.

ReadableStreamBYOBReader.read()

Returns a providing access to the next chunk in the stream's internal queue.

ReadableStreamBYOBReader.releaseLock()

Releases the reader's lock on the stream.

Examples

In the following example, an artifical Response is created to stream HTML fragments fetched from another resource to the browser.

It demonstrates the usage of a ReadableStream in combination with a Uint8Array.

fetch("https://www.example.org/").then((response) => {
  const reader = response.body.getReader();
  const stream = new ReadableStream({
    start(controller) {
      // The following function handles each data chunk
      function push() {
        // "done" is a Boolean and value a "Uint8Array"
        return reader.read().then(({ done, value }) => {
          // Is there no more data to read?
          if (done) {
            // Tell the browser that we have finished sending data
            controller.close();
            return;
          }

          // Get the data and send it to the browser via the controller
          controller.enqueue(value);
        }).then(push);
      };
      
      push();
    }
  });

  return new Response(stream, { headers: { "Content-Type": "text/html" } });
});

Specifications

Browser Compatibility

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