DataView.prototype.byteLength

// Create an ArrayBuffer with a size in bytes
const buffer = new ArrayBuffer(16);

const view1 = new DataView(buffer);
const view2 = new DataView(buffer, 12, 4); // From byte 12 for the next 4 bytes

console.log(view1.byteLength + view2.byteLength); // 16 + 4
// Expected output: 20

const buffer = new ArrayBuffer(8);
const dataview = new DataView(buffer);
dataview.byteLength; // 8 ( byteLength )

const dataview2 = new DataView(buffer, 1, 5);
dataview2.byteLength; // 5 (    DataView)

const dataview3 = new DataView(buffer, 2);
dataview3.byteLength; // 6 (- byteOffset,    DataView)