base64.js

Yet another Base64 transcoder.

Install

$ npm install --save js-base64

Usage

In Browser

Locally…

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

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

<script src="https://cdn.jsdelivr.net/npm/[email protected]/base64.min.js"></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

locally…

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 jsdelivr.net does not automatically minify .mjs
import { Base64 } from 'https://cdn.jsdelivr.net/npm/[email protected]/base64.mjs';
</script>

<script type="module">
// or if you prefer no Base64 namespace
import { encode, decode } from 'https://cdn.jsdelivr.net/npm/[email protected]/base64.mjs';
</script>

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.

require=require('esm')(module);
import {Base64} from 'js-base64';

SYNOPSIS

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); // ZGFua29nYWk 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('Z');    // false: a single character can't encode a byte
Base64.isValid('++');   // true: can be non URL-safe
Base64.isValid('--');   // true: or URL-safe
Base64.isValid('+-');   // false: can't mix both

Base64 variants

The default encoding uses the standard Base64 alphabet from RFC 4648, section 4. The URL-safe form in js-base64 uses the base64url alphabet from section 5 and omits padding.

Form	Characters for values 62 and 63	Padding	Encoding methods
Standard Base64	+ and /	Trailing = as needed	Base64.encode(text), Base64.fromUint8Array(bytes)
URL-safe Base64	- and _	Omitted	Base64.encodeURI(text), Base64.encode(text, true), Base64.fromUint8Array(bytes, true)

For example, these bytes show both the alphabet and padding differences:

const bytes = new Uint8Array([251, 255]);
Base64.fromUint8Array(bytes);       // '+/8='
Base64.fromUint8Array(bytes, true); // '-_8'
Base64.toUint8Array('+/8=');        // Uint8Array [251, 255]
Base64.toUint8Array('-_8');         // Uint8Array [251, 255]

Base64.decode() and Base64.toUint8Array() accept both alphabets, with or without padding. Use decode() for UTF-8 text and toUint8Array() for bytes. Encoded output has no line wrapping; MIME or PEM line wrapping is not added.

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
Base64.extendString();
// 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- an 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();// UTF-8 bytes of '小飼弾'

// you have to explicitly extend Uint8Array.prototype
Base64.extendUint8Array();
// once extended, you can do the following
u8s.toBase64();     // 'ZGFua29nYWk='
u8s.toBase64URI();  // 'ZGFua29nYWk'
u8s.toBase64URL();  // 'ZGFua29nYWk' an alias of .toBase64URI()

// extend all at once
Base64.extendBuiltins()

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

Suppose you have:

var pngBase64 = 
  "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYAAAAAYAAjCB0C8AAAAASUVORK5CYII=";

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().  The same rule applies to the opposite direction.

Or even better, Base64.toUint8Array(pngBase64).

Brief History

• Since version 3.3 it is written in TypeScript. Both base64.mjs and base64.js are compiled from base64.ts via Rollup.
• Since version 3.7 base64.js is ES5-compatible again (hence IE11-compatible).
• Since 3.0 js-base64 switch to ES2015 module so it is no longer compatible with legacy browsers like IE (see above)