phpjs/functions/url/base64_decode.js

php.js offers community built php functions in javascript

function base64_decode(data) {
  //  discuss at: http://phpjs.org/functions/base64_decode/
  // original by: Tyler Akins (http://rumkin.com)
  // improved by: Thunder.m
  // improved by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  // improved by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  //    input by: Aman Gupta
  //    input by: Brett Zamir (http://brett-zamir.me)
  // bugfixed by: Onno Marsman
  // bugfixed by: Pellentesque Malesuada
  // bugfixed by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  //   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'

  var b64 = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
  var o1, o2, o3, h1, h2, h3, h4, bits, i = 0,
    ac = 0,
    dec = '',
    tmp_arr = [];

  if (!data) {
    return data;
  }

  data += '';

  do { // unpack four hexets into three octets using index points in b64
    h1 = b64.indexOf(data.charAt(i++));
    h2 = b64.indexOf(data.charAt(i++));
    h3 = b64.indexOf(data.charAt(i++));
    h4 = b64.indexOf(data.charAt(i++));

    bits = h1 << 18 | h2 << 12 | h3 << 6 | h4;

    o1 = bits >> 16 & 0xff;
    o2 = bits >> 8 & 0xff;
    o3 = bits & 0xff;

    if (h3 == 64) {
      tmp_arr[ac++] = String.fromCharCode(o1);
    } else if (h4 == 64) {
      tmp_arr[ac++] = String.fromCharCode(o1, o2);
    } else {
      tmp_arr[ac++] = String.fromCharCode(o1, o2, o3);
    }
  } while (i < data.length);

  dec = tmp_arr.join('');

  return decodeURIComponent(escape(dec.replace(/\0+$/, '')));
}