How to implement instant notification system using Express + Mongo Rest API?

I am currently building an Ionic app with Express and MongoDB.

How to develop an api or a system to enable instant update to view templates with new data? Also, how to notify a list of user?

event{
	time : time,
	invited : [ ] // send a notification everyone in the list when an event happens
}

I think using SocketIO would be good here. But I can't figure out how to design this. I have read many books and watched some video tutorials but haven't found anybody discussing this .

Your help would be appreciated here.