[LeetCode][JavaScript]Balanced Binary Tree

 1 /**
 2  * Definition for a binary tree node.
 3  * function TreeNode(val) {
 4  *     this.val = val;
 5  *     this.left = this.right = null;
 6  * }
 7  */
 8 /**
 9  * @param {TreeNode} root
10  * @return {boolean}
11  */
12 var isBalanced = function(root) {
13     return treeHeight(root) === -1 ? false : true;
14 
15     /**
16      * @return {int} tree‘s height
17      * return -1 if depth differ of the two subtrees are more than 1
18      */
19     function treeHeight(node){
20         if(node === null) return 0;
21         if(node.left === null && node.right === null) return 1;
22         var leftH = treeHeight(node.left);
23         var rightH = treeHeight(node.right);
24         if(leftH === -1 || rightH === -1) return -1;
25         if(Math.abs(leftH - rightH) > 1) return -1;
26         return Math.max(leftH, rightH) + 1;
27     }
28 };