Diameter of a binary tree

Problem Statement

Given the root of a binary tree, return the length of the diameter of the tree.The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root. The length of a path between two nodes is represented by the number of edges between them.

/**
 * 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)
 * }
 */

/**
 * @param {TreeNode} root
 * @return {number}
 */

var diameterOfBinaryTree = function(root) {
    let maxDiameter = 0;

    function depth(node) {
        if (!node) return 0;

        const leftDepth = depth(node.left);
        const rightDepth = depth(node.right);

        maxDiameter = Math.max(maxDiameter, leftDepth + rightDepth);

        return Math.max(leftDepth, rightDepth) + 1;
    }

    depth(root);
    return maxDiameter;
};