Balanced Binary Tree.js

/*Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as:

a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

Example 1:

Given the following tree [3,9,20,null,null,15,7]:

    3
   / \
  9  20
    /  \
   15   7
Return true.

Example 2:

Given the following tree [1,2,2,3,3,null,null,4,4]:

       1
      / \
     2   2
    / \
   3   3
  / \
 4   4
Return false.*/

/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {TreeNode} root
 * @return {boolean}
 */
var isBalanced = function(root) {
    if(root == null)
        return true
    var diff = depth(root.left) - depth(root.right)
    if(Math.abs(diff) > 1)
        return false
    return isBalanced(root.left) && isBalanced(root.right)
};

var depth = function(node){
    if(node == null)
        return 0
    return 1 + Math.max(depth(node.left), depth(node.right))
}