how to make a factorial function in javascript

1function factorial(n) {
2  if (n < 0) return;
3  if (n < 2) return 1;
4  return n * factorial(n - 1);
5}

1function factorialize(num) {
2  if (num === 0 || num === 1)
3    return 1;
4  for (var i = num - 1; i >= 1; i--) {
5    num *= i;
6  }
7  return num;
8}
9factorialize(5);

1function factorialize(num) {
2  var result = num;
3  if (num === 0 || num === 1) 
4    return 1; 
5  while (num > 1) { 
6    num--;
7    result *= num;
8  }
9  return result;
10}

1// Simple arrow function solution
2var factorial = n => (n <= 0) ? 1: n * factorial(n - 1);

1    function factorial(n) {
2        if (n > 1) {
3            return n * factorial(n - 1);
4        }
5        return 1;
6    }

1const factorial = n => n <= 1 ? 1 : n * factorial(n - 1);
2
3// Examples
4factorial(2);   // 2
5factorial(3);   // 6