PHP's base64_decode in JavaScript

Here’s what our current JavaScript equivalent to PHP's base64_decode looks like.

module.exports = function base64_decode (encodedData) { // eslint-disable-line camelcase
// discuss at: https://locutus.io/php/base64_decode/
// original by: Tyler Akins (https://rumkin.com)
// improved by: Thunder.m
// improved by: Kevin van Zonneveld (https://kvz.io)
// improved by: Kevin van Zonneveld (https://kvz.io)
// input by: Aman Gupta
// input by: Brett Zamir (https://brett-zamir.me)
// bugfixed by: Onno Marsman (https://twitter.com/onnomarsman)
// bugfixed by: Pellentesque Malesuada
// bugfixed by: Kevin van Zonneveld (https://kvz.io)
// improved by: Indigo744
// example 1: base64_decode('S2V2aW4gdmFuIFpvbm5ldmVsZA==')
// returns 1: 'Kevin van Zonneveld'
// example 2: base64_decode('YQ==')
// returns 2: 'a'
// example 3: base64_decode('4pyTIMOgIGxhIG1vZGU=')
// returns 3: '✓ à la mode'
// decodeUTF8string()
// Internal function to decode properly UTF8 string
// Adapted from Solution #1 at https://developer.mozilla.org/en-US/docs/Web/API/WindowBase64/Base64_encoding_and_decoding
const decodeUTF8string = function (str) {
// Going backwards: from bytestream, to percent-encoding, to original string.
return decodeURIComponent(str.split('').map(function (c) {
return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2)
}).join(''))
}
if (typeof window !== 'undefined') {
if (typeof window.atob !== 'undefined') {
return decodeUTF8string(window.atob(encodedData))
}
} else {
return new Buffer(encodedData, 'base64').toString('utf-8')
}
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 dec = ''
const tmpArr = []
if (!encodedData) {
return encodedData
}
encodedData += ''
do {
// unpack four hexets into three octets using index points in b64
h1 = b64.indexOf(encodedData.charAt(i++))
h2 = b64.indexOf(encodedData.charAt(i++))
h3 = b64.indexOf(encodedData.charAt(i++))
h4 = b64.indexOf(encodedData.charAt(i++))
bits = h1 << 18 | h2 << 12 | h3 << 6 | h4
o1 = bits >> 16 & 0xff
o2 = bits >> 8 & 0xff
o3 = bits & 0xff
if (h3 === 64) {
tmpArr[ac++] = String.fromCharCode(o1)
} else if (h4 === 64) {
tmpArr[ac++] = String.fromCharCode(o1, o2)
} else {
tmpArr[ac++] = String.fromCharCode(o1, o2, o3)
}
} while (i < encodedData.length)
dec = tmpArr.join('')
return decodeUTF8string(dec.replace(/\0+$/, ''))
}
[ 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_decode'). You could also require the url module in full so that you could access url.base64_decode 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.

Examples

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_decode('S2V2aW4gdmFuIFpvbm5ldmVsZA==')'Kevin van Zonneveld'
2base64_decode('YQ==')'a'
3base64_decode('4pyTIMOgIGxhIG1vZGU=')'✓ à la mode'

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