calculateFactorial()

Step One: Understand the Problem

Firstly, we need to understand what we are trying to solve. We want to create a function that will take in an integer number as an argument and return the factorial of the number.

The factorial function (symbol: !) means to multiply a series of descending natural numbers. For instance, the factorial of 5 is 5! = 5 * 4 * 3 * 2 * 1 = 120.

Step Two: Initialize the Function

We start by initializing a function named calculateFactorial that takes an argument n. This n is the number we will calculate the factorial of.

function calculateFactorial(n) {

}

Step Three: Set Up the Base Case

Next, we need to handle a base case for our recursive function. If n is 0 (zero), then the function should return 1 since the factorial of 0 is 1.

function calculateFactorial(n) {
  if (n === 0) {
    return 1;
  }
}

Step Four: Recursion

Lastly, for other than zero, the function will call itself, with n being decreased by 1 at each step. This will continue until n is equal to 0, at which point the recursion stops and the results are multiplied together.

function calculateFactorial(n) {
  if (n === 0) {
    return 1;
  }
  return n * calculateFactorial(n - 1);
}

Conclusion

That's it! Our factorial function is ready. Here is the full code for the function :

function calculateFactorial(n) {
  if (n === 0) {
    return 1;
  }
  return n * calculateFactorial(n - 1);
}

You can test this function by calling it with different numbers.

console.log(calculateFactorial(5));  // Outputs: 120
console.log(calculateFactorial(0));  // Outputs: 1
console.log(calculateFactorial(1));  // Outputs: 1
console.log(calculateFactorial(3));  // Outputs: 6

This function works by taking an argument n and then calling itself until n is equal to 0. When n is 0 the function returns 1, this value is then multiplied with the previous value of n and this continues until the initial value of n was reached, giving us our factorial in return.