Lowest Common Ancestor of Deepest Leaves LeetCode solution in JavaScript

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var lcaDeepestLeaves = function (root) {
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  if (!root) return root;
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  // keep track of max depth if node have both deepest node
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  let md = 0,
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    ans = null;
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  const compute = (r = root, d = 0) => {
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    if (!r) {
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      md = Math.max(md, d);
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      return d;
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    }
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    const ld = compute(r.left, d + 1);
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    const rd = compute(r.right, d + 1);
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    if (ld == rd && ld == md) {
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      ans = r;
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    }
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    return Math.max(ld, rd);
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  };
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  compute();
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  return ans;
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};