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DataView.prototype.byteLength

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since ⁨July 2015⁩.

The byteLength accessor property of DataView instances returns the length (in bytes) of this view.

Try it

// 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

Description

The byteLength property is an accessor property whose set accessor function is undefined, meaning that you can only read this property. If the DataView is length-tracking, then its length depends on the length of the underlying buffer, and may change if the buffer is resized. Otherwise, the value is established when the DataView is constructed and cannot be changed. Whether length-tracking or not, the byteLength becomes 0 if the underlying buffer is resized such that the viewed range is no longer valid.

Examples

Using the byteLength property

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

const dataview2 = new DataView(buffer, 1, 5);
dataview2.byteLength; // 5 (as specified when constructing the DataView)

const dataview3 = new DataView(buffer, 2);
dataview3.byteLength; // 6 (due to the offset of the constructed DataView)

const buffer2 = new ArrayBuffer(16, { maxByteLength: 32 });
const dataviewLengthTracking = new DataView(buffer2, 4);
dataviewLengthTracking.byteLength; // 12 (16 - 4)
buffer2.resize(20);
dataviewLengthTracking.byteLength; // 16 (20 - 4)
buffer2.resize(3);
dataviewLengthTracking.byteLength; // 0 (viewed range is no longer valid)

Specifications

Specification
ECMAScript® 2026 Language Specification> # sec-get-dataview.prototype.bytelength>

Browser compatibility

	Desktop					Mobile							Server
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android	WebView on iOS	Bun	Deno	Node.js
`byteLength`	9	12	15	12.1	5.1	18	15	12.1	5	1.0	4	5	1.0.0	1.0	0.10.0