day5：js数组方法reverse的实现

  const arr = [1, 2, 3]

  Array.prototype._reverse = function () {
    const newArr = [];
    for (let i = this.length - 1; i >= 0; i--) {
      newArr[newArr.length] = this[i];
    }
    let k = 0;
    while (k < newArr.length) {
      this[k] = newArr[k];
      k++
    };
    return this;
  }
  console.log(arr._reverse(), arr)
  // 输出结果：[3, 2, 1]，[3, 2, 1]