Binary Tree Inorder Traversal LeetCode solution in JavaScript

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var inorderTraversal = function (root) {
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  let result = [];
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  function traverse(node) {
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    if (!node) {
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      return;
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    }
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    traverse(node.left);
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    result.push(node.val);
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    traverse(node.right);
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  }
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  traverse(root);
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  return result;
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};