cloudcode.js

// LikePhoto.js
exports.main = function(request, response){
  var query = new Parse.Query("Photo");
  var objid = request.params.objectid;

  return query.get(objid)

    // Photo
    .then(function(photo) { 

        // GENERIC LOGIC FOR ALL LIKE PHOTOS here.
        // ...
        return Notifications.sendNotifications(opts);
    }, function(error) {
      // error handler
    })

    // Notification
    .then(function (notif) {
        // notif here will be the returned value of sendNotifications()
        response.success(likesCounter);
    }, function () {
        // Whatever on notification error
    });
};

// Notifications.js
exports.sendNotifications = function (opts) {
    return query.get(userID).then(function (user) {
        // On Success
        // THIS WILL BE GIVEN TO THE NEXT .then() - WHOEVER CALLS sendNotifications().then()
        return addNotification(etc);
    }, function () {
        // Failure
    });
};