docs: function decode(base64string) {
          var number = 0;
          var chars = base64string.split('');
          var len = chars.length;
          var val10;
          var val64;
          var asciiVal;
  
          for (var i = 0; i < len; i++) {
  
              val64 = chars[len - 1 - i];
              asciiVal = val64.charCodeAt(0);
              val10 = 0;
              if (val64 === '_') {
                  val10 = 63;
              }
              else if (val64 === '-') {
                  val10 = 62;
              }
              else if (asciiVal > 96 && asciiVal < 123) {
                  val10 = asciiVal - 61;
              }
              else if (asciiVal > 64 && asciiVal < 91) {
                  val10 = asciiVal - 55;
              }
              else if (asciiVal > 47 && asciiVal < 58) {
                  val10 = asciiVal - 48;
              }
              else {
                  throw new AppError({ msg: 'Non-base64value in encoded string' });
              }
  
              number += (Math.pow(64, i) * val10);
          }
  
          return number;
      }