PHP's base64_decode in JavaScript

module.exports = functionbase64_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.
returndecodeURIComponent(str.split('').map(function (c) {
return'%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2)
    }).join(''))
  }
if (typeofwindow !== 'undefined') {
if (typeofwindow.atob !== 'undefined') {
return decodeUTF8string(window.atob(encodedData))
    }
  } else {
returnnew 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)
    } elseif (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+$/, ''))
}