Web/API/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 StandardThe definition of 'WindowOrWorkerGlobalScope.atob()' in that specification.	Living Standard	Method moved to the `WindowOrWorkerGlobalScope` mixin in the latest spec.
HTML 5.1The definition of 'WindowBase64.atob()' in that specification.	Recommendation	Snapshot of HTML Living Standard. No change.
HTML5The 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

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`atob`	Chrome Full support 4	Edge Full support 12	Firefox Full support 1 Full support 1 Full support 27 Notes' Notes' `atob()` ignores all space characters in the argument to comply with the latest HTML5 spec (see bug 711180). Full support 57 Notes' Notes' `atob()` now defined on `WindowOrWorkerGlobalScope` mixin.	IE Full support 10	Opera Full support 10.5	Safari Full support 3	WebView Android Full support ≤37	Chrome Android Full support 18	Firefox Android Full support 4 Full support 4 Full support 27 Notes' Notes' `atob()` ignores all space characters in the argument to comply with the latest HTML5 spec (see bug 711180). Full support 57 Notes' Notes' `atob()` now defined on `WindowOrWorkerGlobalScope` mixin.	Opera Android Full support 11	Safari iOS Full support 1	Samsung Internet Android Full support 1.0

Legend

Full support: Full support
See implementation notes.': See implementation notes.