Monotone Increasing Digits LeetCode solution in JavaScript

1
var monotoneIncreasingDigits = function (n) {
2
  let arr = String(n).split("");
3
  for (let i = arr.length - 2; i >= 0; i--) {
4
    if (arr[i] > arr[i + 1]) {
5
      arr[i]--;
6
      for (let j = i + 1; j < arr.length; j++) arr[j] = "9";
7
    }
8
  }
9
  return Number(arr.join(""));
10
};