Confused about Recursion

[nicholasgyd]

Hi all, I’m really confused about how this solution works… Need a more detailed explanation. Can anybody help?

function rangeOfNumbers(startNum, endNum) {
if (endNum - startNum === 0) {
  return [startNum];
} else {
  var numbers = rangeOfNumbers(startNum, endNum - 1);
  numbers.push(endNum);
  return numbers;
}
}

Challenge: Use Recursion to Create a Range of Numbers

Link to the challenge:

freeCodeCamp.org

[twotani]

The key point here is that the function calls itself with different parameters in the else case. Suppose we make this first call

var ans = rangeOfNumbers(2, 4);

Inside this function, the if test fails so the else part is executed, making a recursive call

rangeOfNUmbers(2, 3)

Inside this function, again the test fails, so there’s another recursive call

rangeOfNumbers(2,2)

Now, the recursion stops because the if test succeeds and returns [2]. Where does this function return the value to? To its caller, of course. Who called rangeOfNumbers(2,2)? It’s called from inside the function rangeOfNumbers(2,3). The returned value is assigned to numbers and then endNum is added. What is endNum here? 3. So we’re returning [2,3] to the caller, which is from rangeOfNumbers(2,4). The same process is repeated, causing [2, 3, 4] is returned to the caller.
Here’s a simple illustration of the concept.

[nicholasgyd]

That’s an incredibly lucid explanation… Got it! Thank you so much!