https://leetcode.com/problems/invert-binary-tree/

invert-binary-tree.js

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

        var rr, rl;

        rl = invertTree(root.left);
        rr = invertTree(root.right);

        root.left = rr;
        root.right = rl;

    }

    return root;
};