Body.body

The body read-only property of the Body mixin is a simple getter used to expose a ReadableStream of the body contents.

var stream = response.body;

A ReadableStream.

In our simple stream pump example we fetch an image, expose the response's stream using response.body, create a reader using ReadableStream.getReader(), then enqueue that stream's chunks into a second, custom readable stream — effectively creating an identical copy of the image.

const image = document.getElementById('target');

// Fetch the original image
fetch('./tortoise.png')
// Retrieve its body as ReadableStream
.then(response => response.body)
.then(body => {
  const reader = body.getReader();

  return new ReadableStream({
    start(controller) {
      return pump();

      function pump() {
        return reader.read().then(({ done, value }) => {
          // When no more data needs to be consumed, close the stream
          if (done) {
            controller.close();
            return;
          }

          // Enqueue the next data chunk into our target stream
          controller.enqueue(value);
          return pump();
        });
      }
    }
  })
})
.then(stream => new Response(stream))
.then(response => response.blob())
.then(blob => URL.createObjectURL(blob))
.then(url => console.log(image.src = url))
.catch(err => console.error(err));

• Fetch API
• Streams API
• ServiceWorker API