PHP's base64_encode in JavaScript

Here’s what our current JavaScript equivalent to PHP's base64_encode looks like.

module.exports = function base64_encode (stringToEncode) { // eslint-disable-line camelcase
// discuss at:
// original by: Tyler Akins (
// improved by: Bayron Guevara
// improved by: Thunder.m
// improved by: Kevin van Zonneveld (
// improved by: Kevin van Zonneveld (
// improved by: Rafał Kukawski (
// bugfixed by: Pellentesque Malesuada
// improved by: Indigo744
// example 1: base64_encode('Kevin van Zonneveld')
// returns 1: 'S2V2aW4gdmFuIFpvbm5ldmVsZA=='
// example 2: base64_encode('a')
// returns 2: 'YQ=='
// example 3: base64_encode('✓ à la mode')
// returns 3: '4pyTIMOgIGxhIG1vZGU='
// encodeUTF8string()
// Internal function to encode properly UTF8 string
// Adapted from Solution #1 at
const encodeUTF8string = function (str) {
// first we use encodeURIComponent to get percent-encoded UTF-8,
// then we convert the percent encodings into raw bytes which
// can be fed into the base64 encoding algorithm.
return encodeURIComponent(str).replace(/%([0-9A-F]{2})/g,
function toSolidBytes (match, p1) {
return String.fromCharCode('0x' + p1)
if (typeof window !== 'undefined') {
if (typeof window.btoa !== 'undefined') {
return window.btoa(encodeUTF8string(stringToEncode))
} else {
return new Buffer(stringToEncode).toString('base64')
const b64 = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/='
let o1
let o2
let o3
let h1
let h2
let h3
let h4
let bits
let i = 0
let ac = 0
let enc = ''
const tmpArr = []
if (!stringToEncode) {
return stringToEncode
stringToEncode = encodeUTF8string(stringToEncode)
do {
// pack three octets into four hexets
o1 = stringToEncode.charCodeAt(i++)
o2 = stringToEncode.charCodeAt(i++)
o3 = stringToEncode.charCodeAt(i++)
bits = o1 << 16 | o2 << 8 | o3
h1 = bits >> 18 & 0x3f
h2 = bits >> 12 & 0x3f
h3 = bits >> 6 & 0x3f
h4 = bits & 0x3f
// use hexets to index into b64, and append result to encoded string
tmpArr[ac++] = b64.charAt(h1) + b64.charAt(h2) + b64.charAt(h3) + b64.charAt(h4)
} while (i < stringToEncode.length)
enc = tmpArr.join('')
const r = stringToEncode.length % 3
return (r ? enc.slice(0, r - 3) : enc) + '==='.slice(r || 3)
[ View on GitHub | Edit on GitHub | Source on GitHub ]

How to use

You you can install via npm install locutus and require it via require('locutus/php/url/base64_encode'). You could also require the url module in full so that you could access url.base64_encode instead.

If you intend to target the browser, you can then use a module bundler such as Parcel, webpack, Browserify, or rollup.js. This can be important because Locutus allows modern JavaScript in the source files, meaning it may not work in all browsers without a build/transpile step. Locutus does transpile all functions to ES5 before publishing to npm.

A community effort

Not unlike Wikipedia, Locutus is an ongoing community effort. Our philosophy follows The McDonald’s Theory. This means that we don't consider it to be a bad thing that many of our functions are first iterations, which may still have their fair share of issues. We hope that these flaws will inspire others to come up with better ideas.

This way of working also means that we don't offer any production guarantees, and recommend to use Locutus inspiration and learning purposes only.


Please note that these examples are distilled from test cases that automatically verify our functions still work correctly. This could explain some quirky ones.

#codeexpected result
1base64_encode('Kevin van Zonneveld')'S2V2aW4gdmFuIFpvbm5ldmVsZA=='
3base64_encode('✓ à la mode')'4pyTIMOgIGxhIG1vZGU='

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