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    }

1// program to find the factorial of a number
2
3// take input from the user
4const number = parseInt(prompt('Enter a positive integer: '));
5
6// checking if number is negative
7if (number < 0) {
8    console.log('Error! Factorial for negative number does not exist.');
9}
10
11// if number is 0
12else if (number === 0) {
13    console.log(`The factorial of ${number} is 1.`);
14}
15
16// if number is positive
17else {
18    let fact = 1;
19    for (i = 1; i <= number; i++) {
20        fact *= i;
21    }
22    console.log(`The factorial of ${number} is ${fact}.`);
23}
24
25//output
26Enter a positive integer: 5
27The factorial of 5 is 120.