This solution is generated by ChatGPT, correctness is not guaranteed.

AI solution for JavaScript Coding Question on BFE.dev
104. Traverse DOM level by level

One possible solution to traverse the DOM level by level and flatten it into a one dimensional array is to use a queue data structure and a while loop. Here's the code:

function flattenDom(root) {
  let queue = [root];
  let result = [];
  
  while (queue.length > 0) {
    let curr = queue.shift();
    result.push(curr);
    let children = curr.children;
    for (let i = 0; i < children.length; i++) {
      queue.push(children[i]);
    }
  }
  
  return result;
}

In this code, we start with the root element and put it into a queue. Then, in a while loop, we dequeue the first element in the queue, add it to the result array, and enqueue its children (if any) in the order they appear in the DOM. We keep doing this until the queue is empty.

The result array will contain all the elements in the DOM tree in the order of layer by layer, as shown in the illustration.