Construct String from Binary Tree LeetCode solution in JavaScript

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var tree2str = function (root) {
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  // Step 1: Base case - if the root is null, return an empty string
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  if (root === null) return "";
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  // Step 2: Start with the value of the current node as the result string
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  let result = root.val.toString();
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  // Step 3: Recursively process the left and right subtrees
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  let leftSubtree = tree2str(root.left);
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  let rightSubtree = tree2str(root.right);
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  // Step 4: Check conditions to determine the final result
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  if (leftSubtree === "" && rightSubtree === "") {
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    // Both left and right subtrees are empty, return the current result
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    return result;
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  }
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  if (leftSubtree === "") {
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    // Left subtree is empty, include empty parentheses for it and the right subtree
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    return result + "()" + "(" + rightSubtree + ")";
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  }
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  if (rightSubtree === "") {
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    // Right subtree is empty, include the left subtree
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    return result + "(" + leftSubtree + ")";
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  }
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  // Both left and right subtrees are non-empty, include both in the result
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  return result + "(" + leftSubtree + ")" + "(" + rightSubtree + ")";
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};