在数组内置类扩展数组去重的方法

  Array.prototype.myUnique = function (){
      let obj = {};
      for (let i =0;i<this.length;i++){
        let cur = this[i];
        if(obj[cur] == cur){
         this[i] = this[this.length-1];
         this.length--
          i--
        }
        obj[cur] = cur
      }
      obj = null;
      return this;  // 实现链式写法
  }