Отказываемся от коллбэков: Генераторы в ECMAScript 6

var rest = require("../rest");
module.exports = function (app) {

    function *vkPush(vkusers, message) {
        if (!(vkusers instanceof Array))
            throw new Error("vkusers is not array");

        var APP_ID = 11111;
        var APP_SECRET = "xxxxx";
        var uids = [];
        try {
            var url = 'https://oauth.vk.com/access_token?client_id=' + APP_ID + '&client_secret=' + APP_SECRET + '&grant_type=client_credentials';
            var data = yield rest.get(url, vkPush.next); //vkPush.next можно записать как arguments.callee.next
            var token = data.access_token;
            var url = 'https://api.vk.com/method/secure.sendNotification?access_token=' + token + '&v=5.7&user_ids=' + vkusers.join(',') + '&message=' + encodeURI(message) + '&client_secret=' + APP_SECRET;
            var data = yield rest.get(url, vkPush.next);
            if (data.response) {
                uids = uids.concat(data.response.split(","));
                console.log("Received", uids);
            }
        }
        catch (e) {
            console.error(e.stack || e);
        }

        return uids;
    }

    return function *fn(req, res) {
        var table = "notifications";
        var user_id = req.user.id;
        var client_id = req.user.id;
        var id = +req.body.id || +req.query.id;


        // Для асинхронных операций
        var data = {};
        app.db.brodie("Query1", function (err, data) {
            data.query1 = data;
        }.async());

        app.db.brodie("Query2", function (err, data) {
            data.query2 = data;
        }.async());

        app.db.brodie("Query3", function (err, data) {
            data.query3 = data;
        }.async());

        // здесь будет остановка до тех пор пока все запросы не отработают
        yield true;

        try {
            switch (req.method) {
                case "GET":
                    var rows = yield app.db.brodie.query("SELECT * FROM ?? WHERE client_id=? ORDER BY date DESC", [table, client_id], fn.next);
                    res.send(rows);
                    break;

                case "PUT":
                    var message = req.body.text;
                    var data = {
                        client_id: client_id,
                        user_id: user_id,
                        text: message,
                        received: 0,
                        date: new Date()
                    }
                    var vkusers = yield app.db.brodie.query("SELECT * FROM notification_users WHERE client_id=? AND type='vk'", [client_id], fn.next);
                    var receiveUids = yield vkPush.run(vkusers, message);
                    if (receiveUids.length)
                        yield app.db.brodie.query('UPDATE notification_users SET last_send=NOW() WHERE uid IN (?) AND type="vk" AND client_id=?', [receiveUids, client_id], fn.next);

                    data.received = receiveUids.length;
                    var result = yield app.db.brodie.query("INSERT INTO ?? SET ?", [table, data], fn.next);
                    var rows = yield app.db.brodie.query("SELECT * FROM ?? WHERE id=?", [table, result.insertId], fn.next);
                    res.send(rows[0]);
                    break;


                default:
                    res.send(500);
                    break;
            }
        }
        catch (e) {
            console.error(e.stack || e);
        }

    }.fn();
}