The first takeaway is that for every emit, there needs to be an on. This is true whether the sender is the server or the client. It is always best to sit down and map out each event and which direction it is going.

The next idea is that of note, which entails building our app out of loosely coupled modules. Our app.js kicks everything that deals with Express off. Then, it fires the startIo function. While it does pass over an object, we could easily create one and use that. Socket.IO just wants a basic HTTP server. In fact, you can just pass the port, which is what we used in our first couple of Socket.IO applications (Ping-Pong). If we wanted to create an application layer of Socket.IO servers, we could refactor this code out and have all the Socket.IO servers run on separate servers other than Express.