index.js

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @param {TreeNode} p
 * @param {TreeNode} q
 * @return {TreeNode}
 */
var lowestCommonAncestor = function(root, p, q) {
    if (root == p || root == q || !root) {
        return root
    }
    let left = lowestCommonAncestor(root.left, p, q)
    let right = lowestCommonAncestor(root.right, p, q)

    if (left && right) {
        return root
    } else if (left) {
        return left
    } else if (right) {
        return right
    } else {
        return null
    }
};
function TreeNode(val) {
    this.val = val;
    this.left = this.right = null;
}
const root = new TreeNode(4)
root.left = new TreeNode(2)
root.right = new TreeNode(6)
root.left.left = new TreeNode(1)
root.left.right = new TreeNode(3)
root.right.left = new TreeNode(5)
root.right.right = new TreeNode(7)

console.log(lowestCommonAncestor(root, root.right.left, root.right))