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Yet another Base64 transcoder in pure-JS

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Yet another Base64 transcoder.


In version 3.0 js-base64 switch to ES2015 module so it is no longer compatible with legacy browsers like IE (see below). And since version 3.3 it is written in TypeScript. Now base64.mjs is compiled from base64.ts then base64.js is generated from base64.mjs.


$ npm install --save js-base64


In Browser


<script src="base64.js"></script>

… or Directly from CDN. In which case you don't even need to install.

<script src=""></script>

This good old way loads Base64 in the global context (window). Though Base64.noConflict() is made available, you should consider using ES6 Module to avoid tainting window.

As an ES6 Module


import { Base64 } from 'js-base64';
// or if you prefer no Base64 namespace
import { encode, decode } from 'js-base64';

or even remotely.

<script type="module">
// note does not automatically minify .mjs
import { Base64 } from '';
<script type="module">
// or if you prefer no Base64 namespace
import { encode, decode } from '';

node.js (commonjs)

const {Base64} = require('js-base64');

Unlike the case above, the global context is no longer modified.

You can also use esm to import instead of require.

import {Base64} from 'js-base64';


let latin = 'dankogai';
let utf8  = '小飼弾'
let u8s   =  new Uint8Array([100,97,110,107,111,103,97,105]);
Base64.encode(latin);             // ZGFua29nYWk=
Base64.encode(latin, true));      // ZGFua29nYWk skips padding
Base64.encodeURI(latin));         // ZGFua29nYWk
Base64.btoa(latin);               // ZGFua29nYWk=
Base64.btoa(utf8);                // raises exception
Base64.fromUint8Array(u8s);       // ZGFua29nYWk=
Base64.fromUint8Array(u8s, true); // ZGFua29nYW which is URI safe
Base64.encode(utf8);              // 5bCP6aO85by+
Base64.encode(utf8, true)         // 5bCP6aO85by-
Base64.encodeURI(utf8);           // 5bCP6aO85by-
Base64.decode(      'ZGFua29nYWk=');// dankogai
Base64.decode(      'ZGFua29nYWk'); // dankogai
Base64.atob(        'ZGFua29nYWk=');// dankogai
Base64.atob(        '5bCP6aO85by+');// '小飼弾' which is nonsense
Base64.toUint8Array('ZGFua29nYWk=');// u8s above
Base64.decode(      '5bCP6aO85by+');// 小飼弾
// note .decodeURI() is unnecessary since it accepts both flavors
Base64.decode(      '5bCP6aO85by-');// 小飼弾
Base64.isValid(0);      // false: 0 is not string
Base64.isValid('');     // true: a valid Base64-encoded empty byte
Base64.isValid('ZA=='); // true: a valid Base64-encoded 'd'
Base64.isValid('Z A='); // true: whitespaces are okay
Base64.isValid('ZA');   // true: padding ='s can be omitted
Base64.isValid('++');   // true: can be non URL-safe
Base64.isValid('--');   // true: or URL-safe
Base64.isValid('+-');   // false: can't mix both

Built-in Extensions

By default Base64 leaves built-in prototypes untouched. But you can extend them as below.

// you have to explicitly extend String.prototype
// once extended, you can do the following
'dankogai'.toBase64();        // ZGFua29nYWk=
'小飼弾'.toBase64();           // 5bCP6aO85by+
'小飼弾'.toBase64(true);       // 5bCP6aO85by-
'小飼弾'.toBase64URI();        // 5bCP6aO85by- ab alias of .toBase64(true)
'小飼弾'.toBase64URL();        // 5bCP6aO85by- an alias of .toBase64URI()
'ZGFua29nYWk='.fromBase64();  // dankogai
'5bCP6aO85by+'.fromBase64();  // 小飼弾
'5bCP6aO85by-'.fromBase64();  // 小飼弾
'5bCP6aO85by-'.toUint8Array();// u8s above
// you have to explicitly extend String.prototype
// once extended, you can do the following
u8s.toBase64();     // 'ZGFua29nYWk='
u8s.toBase64URI();  // 'ZGFua29nYWk'
u8s.toBase64URL();  // 'ZGFua29nYWk' an alias of .toBase64URI()
// extend all at once

.decode() vs .atob (and .encode() vs btoa())

Suppose you have:

var pngBase64 = 

Which is a Base64-encoded 1x1 transparent PNG, DO NOT USE Base64.decode(pngBase64).  Use Base64.atob(pngBase64) instead.  Base64.decode() decodes to UTF-8 string while Base64.atob() decodes to bytes, which is compatible to browser built-in atob() (Which is absent in node.js).  The same rule applies to the opposite direction.

Or even better, Base64.toUint8Array(pngBase64).

If you really, really need an ES5 version

You can transpiles to an ES5 that runs on IE11. Do the following in your shell.

$ make base64.es5.js
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