Binary Tree Level Order Traversal LeetCode solution in JavaScript

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var levelOrder = function (root) {
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  const result = [];
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  if (root == null) return result;
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  let lvl = 0;
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  let temp = [];
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  let q = new Queue();
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  q.enqueue(root);
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  while (!q.isEmpty()) {
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    let levelSize = q.size();
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    while (levelSize-- != 0) {
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      let node = q.dequeue();
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      temp.push(node.val);
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      // enqueue both children first,
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      // before looking at the next dequeued item
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      if (node.left != null) q.enqueue(node.left);
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      if (node.right != null) q.enqueue(node.right);
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    }
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    result.push(temp);
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    temp = [];
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    lvl += 1;
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  }
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  return result;
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};