1function TreeNode(val, left = null, right = null) {
2    this.val = val;
3    this.left = left;
4    this.right = right;
5}
6
7var sumEvenGrandparent = function(root) {
8    function dfs(node, parent, grandparent) {
9        if (!node) return 0;
10        let total = 0;
11        if (grandparent && grandparent.val % 2 === 0) {
12            total += node.val;
13        }
14        total += dfs(node.left, node, parent);
15        total += dfs(node.right, node, parent);
16        return total;
17    }
18    return dfs(root, null, null);
19};