Flatten a nested array

JavaScript
#1

Hey guys, I have a question regarding one of the challenges in the JavaScript course. I should flatten a nested array without using .flat(). I knew that I would need to use some kind of recursive function but in the end I could not come up with something that would be working properly. Because of that, I looked at the proposed solution and it was quite similar to mine with some differences.

I would like to ask what does this piece of code ...steamrollArray(arr[i]) do? I am quite familiar with spread operator and rest operator, but this time I do not know what is going on.

And I would like to ask why does not for loop in recursive function results in some kind of error. I thought that the recursive function would reset for loop to the beginning every single time and that would result in some kind of en error.

  **Proposed solution**

function steamrollArray(arr) {
  const flattenedArray = [];
  // Loop over array contents
  for (let i = 0; i < arr.length; i++) {
    if (Array.isArray(arr[i])) {
      // Recursively flatten entries that are arrays
      //  and push into the flattenedArray
      flattenedArray.push(...steamrollArray(arr[i]));
    } else {
      // Copy contents that are not arrays
      flattenedArray.push(arr[i]);
    }
  }
  return flattenedArray;
};

// test here
steamrollArray([1, [2], [3, [[4]]]]);

  **Your browser information:**

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36

Challenge: Steamroller

Link to the challenge:

#2

I highly recommend against copying the answer. Habitually copying the answer will hurt your ability to problem-solve.

Instead, I would post your in-progress solution and we can help you fix it.

Iā€™m not sure what this means. Each function call is separate. The scope of all variables in each function call is independent.

I suspect that you may have some flaws in your understanding of variables, function calls, and scopes.

#3

the function returns an array, the spread operator just do its usual thing on that array

1 Like
#4

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