Insufficient Nodes in Root to Leaf Paths LeetCode solution in JavaScript

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var sufficientSubset = function (root, limit) {
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  const MIN = Number.MIN_SAFE_INTEGER;
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  const sum = removeNodes(root, 0);
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  if (sum < limit) return null;
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  return root;
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  function removeNodes(node, prevSum) {
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    if (node == null) return MIN;
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    if (node.left == node.right) return node.val + prevSum;
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    const leftSum = removeNodes(node.left, prevSum + node.val);
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    const rightSum = removeNodes(node.right, prevSum + node.val);
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    if (leftSum < limit) node.left = null;
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    if (rightSum < limit) node.right = null;
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    if (node.left == node.right) return MIN;
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    return node.left == null ? rightSum : leftSum;
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  }
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};