Binary Tree Zigzag Level Order Traversal LeetCode solution in JavaScript

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var zigzagLevelOrder = function (root) {
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  let result = [];
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  if (root == null) return result;
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  let queue = [];
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  let leftToRight = true;
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  queue.push(root);
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  while (queue.length != 0) {
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    let qSize = queue.length;
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    let ans = [];
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    // Processing level
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    for (let i = 0; i < qSize; i++) {
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      let front = queue.shift();
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      let index = leftToRight ? i : qSize - i - 1;
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      ans[index] = front.val;
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      if (front.left) queue.push(front.left);
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      if (front.right) queue.push(front.right);
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    }
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    // changing order of operation
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    leftToRight = !leftToRight;
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    result.push(ans);
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  }
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  return result;
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};