code: function(_string) {
      if ('undefined' == typeof _string) {
        return null;
      }
      else if ('string' != typeof _string) {
        throw new Error('Wrong parameter type');
      }
  
      var str = _string.reverse();
      var ret = 0;
  
      for (var i = 0; i <= (str.length - 1); i++) {
        ret = ret + this.index.indexOf(str.substr(i, 1)) * (this.bcpow(this.index.length, (str.length - 1) - i));
      }
  
      return ret;
    }
docs: [@function] AlphabeticID.decode
  [@description] Decode a short string and return number
  [@param] string
  [@return] integer