Theatob() method of theWindow interface decodes astring of data which has been encoded usingBase64 encoding. You can usetheWindow.btoa() method to encode and transmitdata which may otherwise cause communication problems, then transmit it and use theatob() method to decode the data again. For example, you can encode,transmit, and decode control characters such asASCII values 0 through 31.

Also consider using theUint8Array.fromBase64() method, which creates aUint8Array 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

atob(encodedData)

Parameters

encodedData

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

Return value

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

Exceptions

InvalidCharacterErrorDOMException

Thrown ifencodedData is not valid base64.

Examples

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

For more examples, see theWindow.btoa() method.

Specifications

Browser compatibility

See also

• A polyfill ofatob is available incore-js
• data URLs
• WorkerGlobalScope.atob(): the same method, but in worker scopes.
• Window.btoa()
• Uint8Array.fromBase64()