Steamroller question

JavaScript
1

Hello,

I can’t understand one thing in this tutorial, please see code below:

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

steamrollArray([1, [2], [3, [[4]]]])

My question is: why code is not working without dots at the begining of recursive function call?

 flattenedArray.push(steamrollArray(arr[i]))

If i wrote like this:

 flattenedArray.push(...steamrollArray(arr[i]))

then everything works fine. As I understand, recursive function call should return same result and flattenedArray.push should simply push that result in array?

Thank You very much!

2

steamrollArray returns an array

in this way an array is being pushed to flattenedArray, so no flattening is appening

in this way the elements of the array are being pushed to flattenedArray

add console.log statements and look at the different outcomes with the different ways

1 Like
3

But in this case at second loop iteration:

flattenedArray.push(steamrollArray(arr[i])) //when arr[i] = [2]

shouldn’t return and push to flattenedArray 2, and not an array?

4

I got it, it returns variable flattenedArray, which itself is an array, not a number.
Thank You for Your help!

5

Well, [2] is still an array, so it uses the spread operator to instead push the elements inside the array instead of the array itself

6

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