Recursion example

factorial.js

// 4! = 4 * 3 * 2 * 1
// 5! = 5 * 4 * 3 * 2 * 1
// 1! = 1
// 0! = 1
const factorial = (num) => {
  let total = 1;

  for(let i = 1; i <= num; i++) {
    total *= i;
  }

  return total;
}

const factorialRec = (num) => {
  if(num === 1 || num === 0) return 1;

  return num * factorialRec(num - 1);
};

// 5 * factorialRec(4)
// 5 * 4 * factorialRec(3)
// 5 * 4 * 3 * factorialRec(2)
// 5 * 4 * 3 * 2 * factorialRec(1)
// 5 * 4 * 3 * 2 * 1