The WindowOrWorkerGlobalScope.btoa()
method creates a base-64 encoded ASCII string from a String
object in which each character in the string is treated as a byte of binary data.
Note: Since this function treats each character as a byte of binary data, regardless of the number of bytes which actually make up the character, an InvalidCharacterError
exception is thrown if any character's code point is outside the range 0x00 to 0xFF. See Unicode strings for an example demonstrating how to encode strings with characters outside the 0x00 to 0xFF range
var encodedData = scope.btoa(stringToEncode);
stringToEncode
A string containing the Base64 representation of stringToEncode
.
var encodedData = window.btoa('Hello, world'); // encode a string var decodedData = window.atob(encodedData); // decode the string
You can use this method to encode data which may otherwise cause communication problems, transmit it, then use the
method to decode the data again. For example, you can encode control characters such as ASCII values 0 through 31.atob()
btoa()
is also available to XPCOM components implemented in JavaScript, even though Window
is not the global object in components.
In most browsers, calling btoa()
on a Unicode string will cause an InvalidCharacterError
exception.
One option is to escape any extended characters so that the string you actually encode is an ASCII representation of the original. Consider this example, noted by Johan Sundström:
// ucs-2 string to base64 encoded ascii function utoa(str) { return window.btoa(unescape(encodeURIComponent(str))); } // base64 encoded ascii to ucs-2 string function atou(str) { return decodeURIComponent(escape(window.atob(str))); } // Usage: utoa('✓ à la mode'); // 4pyTIMOgIGxhIG1vZGU= atou('4pyTIMOgIGxhIG1vZGU='); // "✓ à la mode" utoa('I \u2661 Unicode!'); // SSDimaEgVW5pY29kZSE= atou('SSDimaEgVW5pY29kZSE='); // "I ♡ Unicode!"
A better, more faithful and less expensive solution is to use typed arrays to do the conversion.
Specification | Status | Comment |
---|---|---|
HTML Living Standard The definition of 'WindowOrWorkerGlobalScope.btoa()' in that specification. | Living Standard | Method moved to the WindowOrWorkerGlobalScope mixin in the latest spec. |
HTML 5.1 The definition of 'WindowBase64.btoa()' in that specification. | Recommendation | Snapshot of HTML Living Standard. No change. |
HTML5 The definition of 'WindowBase64.btoa()' in that specification. | Recommendation | Snapshot of HTML Living Standard. Creation of WindowBase64 (properties where on the target before it). |
Desktop | ||||||
---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | |
Basic support | Yes | Yes | 1
|
10 | Yes | Yes |
Mobile | |||||||
---|---|---|---|---|---|---|---|
Android webview | Chrome for Android | Edge Mobile | Firefox for Android | Opera for Android | iOS Safari | Samsung Internet | |
Basic support | Yes | Yes | ? | 4
|
? | Yes | ? |
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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/btoa