Construct Binary Tree from Preorder and Inorder 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[]} preorder
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 * @param {number[]} inorder
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 * @return {TreeNode}
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 */
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var buildTree = function (preorder, inorder) {
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  let idx = 0;
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  function create(inorderStart, inorderEnd) {
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    if (idx === preorder.length || inorderStart > inorderEnd) {
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      return null;
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    }
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    const root = new TreeNode(preorder[idx]);
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    const mid = inorder.indexOf(preorder[idx]);
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    idx++;
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    root.left = create(inorderStart, mid - 1);
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    root.right = create(mid + 1, inorderEnd);
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    return root;
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  }
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  return create(0, inorder.length - 1);
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};