Question about flattening an array

[showcasefreedom]

0

I understand the concept of what is happening, but I’m trying to grasp the how it is happening. Once I get to this line, flat = flat.concat(flatten(arr[i])), I am a little unclear as to how that specific subarray that is about to be looped through makes it to flat = [ ]. I understand once the function is called again, the sub array is basically being worked on as if it was not a sub array, and starts going though the loop. The arr[i] makes it down to flat.push(arr[i]); Is it at that point that the arr[i] items are being pushed into flat = [ ], or are they being pushed/ directed here flat.concat(flatten(arr[i])) to be resolved and concat’ed when the sub array has finished going through the loop? What is confusing to me is, if they are just be pushed straight into the flat = [ ] using flat.push(arr[i]), what is there to .concat? No info/ data would be there to be able to concat on this line flat.concat(flatten(arr[i])) Any clarity would be greatly appreciated!!

 const arr = [[1, 2, 3], [4, [5, 6]], [[7], [8, [9]]], 10]

 function flatten(arr) {
     let flat = [] ;
     for (let i = 0; i < arr.length; i++) {
       if (Array.isArray(arr[i])) {
         flat = flat.concat(flatten(arr[i]));
       } else {
         flat.push(arr[i]);
       }
     }
     return flat ;
   }

[hbar1st]

Hello, I have edited your subject line to include a more helpful description of this topic. Hopefully this will help you get some good answers as well.

[admit8490]

This is from Steamroller guide page?

Here is some recursion going on, that means two things:

1. explanation would be verbose(I don’t have skills to provide laconic explanation about recursion)
2. running this code here may be helpful to understand what’s going on exactly