Let’s write a function that takes a number as input and logs numbers to the console starting from the number taken as input down to 0.

const countdown = num => {
  for (let i = num; i >= 0; i--) {
    console.log(i)
  }
}

countdown(5)
// 5
// 4
// 3
// 2
// 1
// 0

We use a for loop to implement the countdown function. Using recursion, we can write the countdown function as follows:

const countdown = num => {
  console.log(num)

  num > 0 && countdown(num - 1)
}

countdown(5)
// 5
// 4
// 3
// 2
// 1
// 0

In the recursive implementation, the function countdown calls itself.

In order to stop the recursion from continuing forever, we execute the countdown function only when num > 0.

The Base Case

In recursion terminology, the case in which our function will not recurse is known as the base case. In our case, 0 is the base case for our countdown function.

Every recursive function needs at least one base case to prevent it from calling itself indefinitely.