function fac(n) {
  if (n == 0)
    return 1;
  else
    return fac(n - 1) * n;
}
console.log(fac(4));

function fac(n) {
  if (n == 0)
    return 1;
  else
    return fac(n - 1) * n;
}
console.log(fac(4));

fac(3) * 4;
fac(2) * 3 * 4;
fac(1) * 2 * 3 * 4;
fac(0) * 1 * 2 * 3 * 4;
1 * 1 * 2 * 3 * 4;