Cousins in Binary Tree LeetCode solution in JavaScript

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var isCousins = function (root, x, y) {
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  let xHeight = 1;
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  let xParent = null;
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  let yHeight = 1;
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  let yParent = null;
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  const helper = (node, depth, parent) => {
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    if (node === null) return null;
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    helper(node.left, depth + 1, node);
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    helper(node.right, depth + 1, node);
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    let val = node.val;
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    if (val === x) {
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      xHeight = depth;
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      xParent = parent;
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    }
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    if (val === y) {
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      yHeight = depth;
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      yParent = parent;
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    }
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  };
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  helper(root, 0);
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  return xHeight === yHeight && xParent !== yParent ? true : false;
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};