That is going to happen over in server.js. We can make that the very first event just above createMessage, socket.on('join'):
socket.on('join');
Now as we already know we are going to be taking some arguments in the callback function. We're going to get our parameters. We can call these params, and get that callback function since we are setting up acknowledgments:
socket.on('join', (params, callback) => {});
Inside the join function, the first thing that we want to do is actually validate the data that came through, both the name and the room. These are both potential properties on params. All we really care is that they are non-empty strings; meaning that it's not just a space, not just an empty string, ...
