Basic JavaScript - Use Recursion to Create a Countdown

JavaScript
1

Hi could someone please explain to me how does the unshift function works in this recursion I really dont understand. I’ve watched countless videos and read articles I cant see to grasp how and why it adds the number 5 at the beginning.

// Only change code below this line
function countdown(n){
if (n < 1){
  return [];
} else {
  const x = countdown(n-1);
  x.unshift(n); 
return x

}
  
}
// Only change code above this line
console.log(countdown(5));

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Challenge: Basic JavaScript - Use Recursion to Create a Countdown

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2

Are you saying you don’t know what the unshift method does? Is so, how were you able to solve this?

If you know what the unshift method does then you should know why it adds the number n to the beginning of the array x.

3

i know its the opposite of push

4

I’m assuming you understand that push adds an element to the end an array. So then unshift adds an element to the beginning of an array.

Thus, if your initial function call is:

countdown(5)

Then the else block will be executed, and n being equal to 5 will give you:

  const x = countdown(4);
  x.unshift(5); 
  return x

Since countdown always returns an array, then x will be an array and thus x.unshift(5) will add 5 to the beginning the array stored in x. Thus, 5 will be at the beginning of the array that is returned.

1 Like
5

thank u I think my brain was fried yesterday it makes sense now