Decoding string in Javascript encoded in PHP by base64_encode() function, can output unwanted results. Especially when you have some special characters encoded in PHP side.
For example, if you encode this name "József" you will get the base64 encoded string which looks like this:

                    <?php

$encoded_string = base64_encode('József');
echo $encoded_string; // => SsOzenNlZiA=

?>

Decoding in JavaScript should be easy, if you just use this command:

                    var decoded_string = atob('SsOzenNlZiA=');

output will be not what we are expecting, you will get something like this:

                    console.log(decoded_string); // => József

 

So in order to have proper decoding of PHP base64 encoded string we need to use this class which can be found on http://www.webtoolkit.info

                    /**

*

*  Base64 encode / decode

*  http://www.webtoolkit.info/

**/

var Base64 = {

    // private property
    _keyStr : "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",

    // public method for encoding
    encode : function (input) {
      var output = "";
      var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
      var i = 0;

      input = Base64._utf8_encode(input);

      while (i < input.length) {

        chr1 = input.charCodeAt(i++);
        chr2 = input.charCodeAt(i++);
        chr3 = input.charCodeAt(i++);

        enc1 = chr1 >> 2;
        enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
        enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
        enc4 = chr3 & 63;

        if (isNaN(chr2)) {
          enc3 = enc4 = 64;
        } else if (isNaN(chr3)) {
          enc4 = 64;
        }

        output = output +
        this._keyStr.charAt(enc1) + this._keyStr.charAt(enc2) +
        this._keyStr.charAt(enc3) + this._keyStr.charAt(enc4);

      }

      return output;
    },

    // public method for decoding
    decode : function (input) {
      var output = "";
      var chr1, chr2, chr3;
      var enc1, enc2, enc3, enc4;
      var i = 0;

      input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");

      while (i < input.length) {

        enc1 = this._keyStr.indexOf(input.charAt(i++));
        enc2 = this._keyStr.indexOf(input.charAt(i++));
        enc3 = this._keyStr.indexOf(input.charAt(i++));
        enc4 = this._keyStr.indexOf(input.charAt(i++));

        chr1 = (enc1 << 2) | (enc2 >> 4);
        chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);
        chr3 = ((enc3 & 3) << 6) | enc4;

        output = output + String.fromCharCode(chr1);

        if (enc3 != 64) {
          output = output + String.fromCharCode(chr2);
        }
        if (enc4 != 64) {
          output = output + String.fromCharCode(chr3);
        }

      }

      output = Base64._utf8_decode(output);

      return output;

    },

    // private method for UTF-8 encoding
    _utf8_encode : function (string) {
      string = string.replace(/\r\n/g,"\n");
      var utftext = "";

      for (var n = 0; n < string.length; n++) {

        var c = string.charCodeAt(n);

        if (c < 128) {
          utftext += String.fromCharCode(c);
        }
        else if((c > 127) && (c < 2048)) {
          utftext += String.fromCharCode((c >> 6) | 192);
          utftext += String.fromCharCode((c & 63) | 128);
        }
        else {
          utftext += String.fromCharCode((c >> 12) | 224);
          utftext += String.fromCharCode(((c >> 6) & 63) | 128);
          utftext += String.fromCharCode((c & 63) | 128);
        }

      }

      return utftext;
    },

    // private method for UTF-8 decoding
    _utf8_decode : function (utftext) {
      var string = "";
      var i = 0;
      var c = c1 = c2 = 0;

      while ( i < utftext.length ) {

        c = utftext.charCodeAt(i);

        if (c < 128) {
          string += String.fromCharCode(c);
          i++;
        }
        else if((c > 191) && (c < 224)) {
          c2 = utftext.charCodeAt(i+1);
          string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));
          i += 2;
        }
        else {
          c2 = utftext.charCodeAt(i+1);
          c3 = utftext.charCodeAt(i+2);
          string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));
          i += 3;
        }

      }

      return string;
    }

  }

 

And now if use this snippet, we should get correct result:

                    var decoded_string = Base64.decode('SsOzenNlZiA=');
console.log(decoded_string); // => József