Delete Node in a BST 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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const getLeftMostNode = (root) => {
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  if (!root) return null;
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  let node = getLeftMostNode(root.left);
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  return node ? node : root;
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};
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/**
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 * @param {TreeNode} root
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 * @param {number} key
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 * @return {TreeNode}
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 */
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var deleteNode = function (root, key) {
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  if (!root) return null;
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  if (root.val > key) {
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    root.left = deleteNode(root.left, key);
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  } else if (root.val < key) {
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    root.right = deleteNode(root.right, key);
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  } else {
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    if (!root.left) return root.right;
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    if (!root.right) return root.left;
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    let succ_node = getLeftMostNode(root.right);
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    root.val = succ_node.val;
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    root.right = deleteNode(root.right, succ_node.val);
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  }
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  return root;
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};