如何模拟实现 Array.prototype.splice#前端面试

Array.prototype._splice = function(start, deleteCount, ...items) {
  if (start > 0) {
    if (start > this.length - 1) {
      start = this.length - 1;
    }
  } else  {
    if (Math.abs(start) > this.length - 1) {
      start = 0;
    } else {
      start = this.length - 1 + start;
    }
  }

  const newArr = [];
  const removed = [];

  deleteCount = isNaN(Number(deleteCount)) ? 0 : Number(deleteCount);

  for (let i = 0; i < this.length; i++) {
    if (i < start || i > start + deleteCount - 1) {
      newArr.push(this[i]);
    } else {
      removed.push(this[i])
    }
    if (i === start + deleteCount - 1) {
      newArr.push(...items)
    }
  }

  for (let i = 0; i < newArr.length; i++) {
    this[i] = newArr[i];
  }

  this.length = newArr.length;

  return removed;
}