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

var buffer = new ArrayBuffer(8);
var dataview = new DataView(buffer);
dataview.byteLength; // 8 (matches the byteLength of the buffer)
var dataview2 = new DataView(buffer, 1, 5);
dataview2.byteLength; // 5 (as specified when constructing the DataView)
var dataview3 = new DataView(buffer, 2);
dataview3.byteLength; // 6 (due to the offset of the constructed DataView)