Array.prototype._splice = function (start, count, ...item) {
        let arr = this;
        let range = start + count;
        let res = [];
        for (let i = start; i < range; i++) {
          res.push(arr[i]);
        }
        const startRange = arr.slice(0, start);
        const endRange = arr.slice(start + count, arr.length);
        const newArr = [...startRange, ...item, ...endRange];
        for (let j = 0; j < newArr.length; j++) {
          this[j] = newArr[j];
          this.length--;
        }
        return res;
      };
      let list = [1, 2, 3, 4];
      let a = list._splice(0, 2,5);
      console.log(list);
      console.log(a);