WindowOrWorkerGlobalScope.atob

The WindowOrWorkerGlobalScope.atob() function decodes a string of data which has been encoded using base-64 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 this note at Base64 encoding and decoding and this note at btoa().

Syntax

var decodedData = scope.atob(encodedData);

Throws

Throws a DOMException if the length of passed-in string is not a multiple of 4.

Example

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

Specifications

Specification	Status	Comment
WHATWG HTML Living Standard The definition of 'WindowOrWorkerGlobalScope.atob()' in that specification.	Living Standard	Method moved to the WindowOrWorkerGlobalScope mixin in the latest spec.
WHATWG HTML Living Standard The definition of 'WindowBase64.atob()' in that specification.	Living Standard	No change since the latest snapshot, HTML5.1.
HTML5.1 The definition of 'WindowBase64.atob()' in that specification.	Recommendation	Snapshot of WHATWG HTML Living Standard. No change.
HTML5 The definition of 'WindowBase64.atob()' in that specification.	Recommendation	Snapshot of WHATWG HTML Living Standard. Creation of WindowBase64 (properties were on the target before it).

Browser compatibility

[1] atob() is also available to XPCOM components implemented in JavaScript, even though window is not the global object in components.

[2] Starting with Firefox 27, atob() ignores all space characters in the argument to comply with the latest HTML5 spec (see bug 711180).

[3] atob() now defined on WindowOrWorkerGlobalScope mixin.

See also

• Base64 encoding and decoding
• data URIs
• window.btoa()
• Components.utils.importGlobalProperties