Delete Node in a BST.js

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */

const getLeftMostNode=(root)=>{
    if(!root)return null;
    let node=getLeftMostNode(root.left);
    return node?node:root;
}
/**
 * @param {TreeNode} root
 * @param {number} key
 * @return {TreeNode}
 */


var deleteNode = function(root, key) {
    if(!root)return null;
    if(root.val>key){
    root.left=deleteNode(root.left,key);
    }else if(root.val<key){
    root.right= deleteNode(root.right,key);
    }else{
        if(!root.left)return root.right;
        if(!root.right)return root.left;
        let succ_node=getLeftMostNode(root.right);
        root.val=succ_node.val;
        root.right= deleteNode(root.right,succ_node.val);
        
    }
    return root;

};