LeetCode: Create Target Array In The Given Order Solution

1var createTargetArray = function (nums, index) {
2  const N = nums.length
3  let res = Array(N).fill(null)
4  for (let i = 0; i < N; i++) {
5    if (res[index[i]] == null) {
6      res[index[i]] = nums[i]
7    } else {
8      res = [res.slice(0, index[i]), nums[i], res.slice(index[i])].flat()
9    }
10  }
11  return res.filter(x => x !== null)
12}