LinkList.prototype.update = function (position,newData) {
          if (position < 0 || position >= this.length) return false;
          //获取对应的data
          var current = this.head;
          var index = 0;
          while (index++ < position) {
            current = current.next;
          }
          //将数据替换
           current.data=newData;
           return true
        };