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    }

1num = 5
2factorialn = 1
3function factorial() {
4    for (i = 1; i <= num; i++) {
5        factorialn *= i
6    }
7}
8factorial()
9console.log(factorialn)