DataView.prototype.byteOffset

// Create an ArrayBuffer with a size in bytes
const buffer = new ArrayBuffer(16);
const view = new DataView(buffer, 12, 4); // From byte 12 for the next 4 bytes
console.log(view.byteOffset);
// Expected output: 12

var buffer = new ArrayBuffer(8);
var dataview = new DataView(buffer);
dataview.byteOffset; // 0 (no offset specified)
var dataview2 = new DataView(buffer, 3);
dataview2.byteOffset; // 3 (as specified when constructing the DataView)