text: /**
   * Created by Administrator on 2015/10/15.
   */
  module.exports = RandomWord;
  
  function RandomWord(chars){
      if(!(this instanceof RandomWord)){
          return new RandomWord(chars);
      }
      this._chars = "";
      if(chars){
          this.add(chars);
      }
  }
  
  RandomWord.prototype = {
      add:function(chars){
          this._chars += chars;
          return this;
      },
      random:function(size){
          var len = this._chars.length;
          if(len === 0){
              throw new Error('no chars,please use add(chars)');
          }
          var word = "";
          for(var i=0;i<size;i++){
              var cpo = parseInt(Math.random()*len);
              word += this._chars.charAt(cpo);
          }
          return word;
      }
  }