Greatest English Letter in Upper and Lower Case LeetCode solution in JavaScript

1
var greatestLetter = function (s) {
2
  let set = new Set(s.split(""));
3
  // ASCII(A-Z, a-z)=(65-90, 97-122).
4
  for (let i = 90; i >= 65; i--) {
5
    if (
6
      set.has(String.fromCharCode(i)) &&
7
      set.has(String.fromCharCode(i + 32))
8
    ) {
9
      return String.fromCharCode(i);
10
    }
11
  }
12
  return "";
13
};