Count Good Nodes in Binary Tree LeetCode solution in JavaScript

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var goodNodes = function (root) {
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  let ans = 0;
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  const traverse = (r = root, mx = root.val) => {
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    if (!r) return;
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    if (r.val >= mx) {
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      ans++;
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    }
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    let childMax = Math.max(mx, r.val);
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    traverse(r.left, childMax);
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    traverse(r.right, childMax);
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  };
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  traverse();
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  return ans;
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};