Calculating the factorial of a number

For our first example of recursion, let’s take a look at how to compute the factorial of a number. A factorial of a number, n, is defined by n! and it is the result of multiplying the numbers from 1 to n.

The factorial of 5 is represented by 5! and it is equal to 5 * 4 * 3 * 2 * 1, resulting in 120.

Iterative factorial

If we try to represent the steps to compute the factorial of any number n, we can define the steps as follows: (n) * (n - 1) * (n - 2) * (n - 3) * ... * 1.

We can write a function to compute the factorial of a number using a loop as demonstrated:

functionfactorialIterative(number) {if (number < 0) returnundefined;
  let total = 1;
  for (let n = number; n > 1; n--) {
    total  = total * n;
  }
  return total;
}
console.log(factorialIterative(5)); // 120

We can start computing the factorial starting at the given number, and decrease n until it has a value of 2 since the factorial of 1 is 1 and it is already included in the total variable...