PHP's base64_decode in JavaScript

How to use

You you can install via yarn add locutus and require this function via const base64_decode = require('locutus/php/url/base64_decode').

It is important to use a bundler that supports tree-shaking so that you only ship the functions that you actually use to your browser, instead of all of Locutus, which is massive. Examples are: Parcel, webpack, or rollup.js. For server-side use this is typically less of a concern.

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.

#	code	expected result
1	base64_decode('S2V2aW4gdmFuIFpvbm5ldmVsZA==')	'Kevin van Zonneveld'
2	base64_decode('YQ==')	'a'
3	base64_decode('4pyTIMOgIGxhIG1vZGU=')	'✓ à la mode'

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

module.exports = function base64_decode(encodedData) {
  //  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+$/, ''))
}

A community effort

Not unlike Wikipedia, Locutus is an ongoing community effort. Our philosophy follows The McDonald’s Theory. This means that we assimilate first iterations with imperfections, hoping for others to take issue with-and improve them. This unorthodox approach has worked very well to foster fun and fruitful collaboration, but please be reminded to use our creations at your own risk. THE SOFTWARE IS PROVIDED "AS IS" has never been more true than for Locutus.

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