Construct Binary Tree from Inorder and Postorder Traversal LeetCode solution in JavaScript

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/**
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 * Definition for a binary tree node.
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 * function TreeNode(val, left, right) {
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 * this.val = (val===undefined ? 0 : val)
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 * this.left = (left===undefined ? null : left)
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 * this.right = (right===undefined ? null : right)
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 * }
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 */
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/**
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 * @param {number[]} inorder
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 * @param {number[]} postorder
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 * @return {TreeNode}
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 */
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var buildTree = function (inorder, postorder) {
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  let postIndex = postorder.length - 1;
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  const dfs = (left, right) => {
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    if (left > right) return null;
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    const val = postorder[postIndex--];
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    const mid = inorder.findIndex((e) => e === val);
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    const root = new TreeNode(val);
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    root.right = dfs(mid + 1, right);
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    root.left = dfs(left, mid - 1);
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    return root;
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  };
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  return dfs(0, inorder.length - 1);
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};