Replace elements with greatest element on right side

Link : https://leetcode.com/problems/replace-elements-with-greatest-element-on-right-side/description/

solution 1

var replaceElements = function (arr) {
  if (arr.length === 1) {
    return [-1];
  }

  let max = -1;
  let a;
  for (let i = arr.length - 1; i >= 0; --i) {
    a = arr[i];
    arr[i] = max;
    if (max < a) {
      max = a;
    }
  }
  return arr;
};