Cannot understand how Function Recursion Works on this Problem (even if I figured out the solution)

JavaScript
15

Hello! After searching google, posting in the forum and reviewing the reply, and reading this thread, still don’t understand the example code. As usually happens when I am having difficulty understanding, read-search-ask only leads to more confusion.

Below is my question and a forum reply, with my comments/questions. I would appreciate any help. Thanks!

can anyone please explain what is happening in the example code (especially after the ‘else’). I do not understand the code even after reading (several times) the explanation provided. In the forum I see a lot of references for how to write the correct solution code but I don’t understand the example code so I’m unable to figure out where to start with the solution. Thank you.

function countup(n) {
  if (n < 1) {
    return [];
  } else {
    const countArray = countup(n - 1);
    countArray.push(n);
    return countArray;
  }
}
console.log(countup(5)); // [ 1, 2, 3, 4, 5 ]

Reply

Ethanefung

14h

first think of ‘n’ as 5.
if n is less than 1 then return an array,
else (if the n is greater or equal 1) get the return value of countup(5-1) and push to that value n (which is 5).

what is the value of countup(5-1) in other words countup(4) ?
‘n’ in this context is 4.

if n is less than 1 it return an array,
else (if the n is greater or equal to 1) get the value of countup(4-1) and push to that value ‘n’ ( which is 4).

a question for you.
what is the value of countup(4-1) ?

SolutionReply

Sharad823

14h

Thank you for your response.

first think of ‘n’ as 5. Ok, I understand this
if n is less than 1 then return an array, yes I understand this
else (if the n is greater or equal 1) get the return value of countup(5-1) and push to that value n (which is 5). what is the return value of ‘countup(5-1)’?

what is the value of countup(5-1) in other words countup(4) ?
‘n’ in this context is 4. how does n become 4? n-1 is 4, but how does n become 4? How can n be the same as n-1?

if n is less than 1 it return an array,
else (if the n is greater or equal to 1) get the value of countup(4-1) and push to that value ‘n’ ( which is 4). Again, I don’t understand how the value of n has changed. we called the function with ‘5’ so how can it now be 4? n-1 is 4, but ‘n’ itself is still 5, right?

a question for you.
what is the value of countup(4-1) ? this would be countup(3)

Also - I think .push is used to add to the end of an array, but where are we actually creating the array to add to?