WindowOrWorkerGlobalScope.atob()

The WindowOrWorkerGlobalScope.atob() function decodes a string of data which has been encoded using Base64 encoding. You can use the 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.

For use with Unicode or UTF-8 strings, see the note on "Unicode strings" in the page for btoa().

Syntax

var decodedData = scope.atob(encodedData);

Parameters

encodedData
A binary string contains an base64 encoded data.

Return value

An ASCII string containing decoded data from encodedData.

Exceptions

DOMException (name: InvalidCharacterError)
Throws if encodedData is not valid base64.

Example

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

Polyfill

You can use a polifill from https://github.com/MaxArt2501/base64-js/blob/master/base64.js for browsers that don't support it.

Specifications

Specification Status Comment
HTML Living Standard
The definition of 'WindowOrWorkerGlobalScope.atob()' in that specification.
Living Standard Method moved to the WindowOrWorkerGlobalScope mixin in the latest spec.
HTML 5.1
The definition of 'WindowBase64.atob()' in that specification.
Recommendation Snapshot of HTML Living Standard. No change.
HTML5
The definition of 'WindowBase64.atob()' in that specification.
Recommendation Snapshot of HTML Living Standard. Creation of WindowBase64 (properties where on the target before it).

Browser compatibility

BCD tables only load in the browser

See also