files/en-us/web/javascript/reference/global_objects/dataview/bytelength/index.md

---
title: DataView.prototype.byteLength
short-title: byteLength
slug: Web/JavaScript/Reference/Global_Objects/DataView/byteLength
page-type: javascript-instance-accessor-property
browser-compat: javascript.builtins.DataView.byteLength
sidebar: jsref
---

The **`byteLength`** accessor property of {{jsxref("DataView")}} instances returns the length (in bytes) of this view.

{{InteractiveExample("JavaScript Demo: DataView.prototype.byteLength")}}

```js interactive-example
// 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](/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray#behavior_when_viewing_a_resizable_buffer), 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length-tracking or not, the `byteLength` becomes 0 if the underlying buffer is resized such that the viewed range is no longer valid.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

```js
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dataviewLengthTracking.byteLength; // 0 (viewed range is no longer valid)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

{{Specifications}}

## Browser compatibility

{{Compat}}

## See also

- [JavaScript typed arrays](/en-US/docs/Web/JavaScript/Guide/Typed_arrays) guide
- {{jsxref("DataView")}}
- {{jsxref("ArrayBuffer")}}
- {{jsxref("SharedArrayBuffer")}}