如何模拟实现 Array.prototype.splice

Array.prototype._splice = function (start, deleteCount, ...addList) {
  // 如果start为负数，那么就从倒数的元素算起
  if (start < 0) {
      if (Math.abs(start) > this.length) {
          start = 0
      } else {
          start += this.length
      }
  }

  // 如果没有传deleteCount，那么默认
  if (typeof deleteCount === 'undefined') {
      deleteCount = this.length - start
  }

  // 删除的元素列表
  const removeList =  this.slice(start, start + deleteCount)

  // 删除元素右侧的元素列表
  const right = this.slice(start + deleteCount)

  let addIndex = start
  addList.concat(right).forEach(item => {
      this[addIndex] = item
      addIndex++
  })
  this.length = addIndex

  // 返回删除列表
  return removeList
}