An ArrayBuffer is an opaque representation of bytes available in memory. It is likened to a Blob which is an opaque representation of data available on a disk.

Its constructor takes a parameter which is the length in bytes like so:

 const myBuffer = new ArrayBuffer(64);

The value of an ArrayBuffer has a read-only property: byteLength - which expresses its length in bytes.

It provides a slice() instance method which creates a new ArrayBuffer from an existing one, taking a begin position and an optional length.

const myBuffer = new ArrayBuffer(64);
const slicedBuffer = myBuffer.slice(32, 8);

Fetching Data from the web as an ArrayBuffer

A blob can be dowloaded from the web and stored into an ArrayBuffer using XHR:

const downloadBlob = (url, cb) => {
    const xhr = new XMLHttpRequest();
    xhr.open('GET', url);
    xhr.responseType = 'arraybuffer';
    xhr.onload = () =>  cb(xhr.response);
    xhr.send(null);
 }

That's all guys :)