Window: atob() method

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2016.

The atob() method of the Window interface decodes a string of data which has been encoded using Base64 encoding. You can use the Window.btoa() method to encode and transmit data which may otherwise cause communication problems, then transmit it and use the atob() method to decode the data again. For example, you can encode, transmit, and decode control characters such as ASCII values 0 through 31.

Also consider using the Uint8Array.fromBase64() method, which creates a Uint8Array object from a base64-encoded string. It results in a byte array, which is easier to work with than a string containing raw bytes.

Syntax

js
atob(encodedData)

Parameters

encodedData

A base64-encoded string, using the alphabet produced by Window.btoa().

Return value

A binary string containing raw bytes decoded from encodedData. Strings in JavaScript are encoded as UTF-16, so this means each character must have a code point less than 256, representing one byte of data.

Exceptions

InvalidCharacterError DOMException

Thrown if encodedData is not valid base64.

Examples

js
const encodedData = window.btoa("Hello, world"); // encode a string
const decodedData = window.atob(encodedData); // decode the string

For more examples, see the Window.btoa() method.

Specifications

Specification
HTML
# dom-atob-dev

Browser compatibility

See also