javascript convert number to spreadsheet column

1// converts numbers to spreadsheet letter columns eg. 1 -> A
2function numToSSColumn(num){
3  let s = '', t;
4
5  while (num > 0) {
6    t = (num - 1) % 26;
7    s = String.fromCharCode(65 + t) + s;
8    num = (num - t)/26 | 0;
9  }
10  return s || undefined;
11}
12
13numToSSColumn(0); // undefined
14numToSSColumn(1); // A
15numToSSColumn(26); // Z
16numToSSColumn(-1); // undefined
17numToSSColumn(27); // AA
18numToSSColumn(475254); // ZZZZ