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

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
atobChrome Full support 4Edge Full support 12Firefox 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 10Opera Full support 10.5Safari Full support 3WebView Android Full support ≤37Chrome Android Full support 18Firefox 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 11Safari iOS Full support 1Samsung Internet Android Full support 1.0

Legend

Full support  
Full support
See implementation notes.
See implementation notes.

See also