docs: function genUID(len){
      function base36(val){
        return Math.round(val).toString(36);
      }
  
      // uid should starts with alpha
      var result = base36(10 + 25 * Math.random());
  
      if (!len)
        len = 16;
  
      while (result.length < len)
        result += base36(new Date * Math.random());
  
      return result.substr(0, len);
    }