Message Queues

Socket.io Chat Example

1. Explain to a non-technical recruiter what the Chat Example (above) does.

I uses socket.io to connect users, emmitting events to create a system where users can receive and respond to one another.

2. What proof of life are we getting on the backend from the above app?

The server logs the events as the users drive events

3. Socket.IO gives us the i0.emit() method to send an event to everyone. What flag would you use if you want to send a message to everyone except for a certain emitting socket?

broadcast

Rooms

1. What is a room and how might a room be useful?

A room is an arbitrary channel that sockets can join and leave. It can be used to broadcast events to a subset of clients. Rooms are a tool in socket.io servers for keeping track of groups of connected users. You can then iterate the sockets in a room or broadcast to all of them.

Uses:

• broadcast data to each device / tab of a given user
• send notifications about a given entity

2. How do you join a room?

You can call join to subscribe the socket to a given channel:

io.on("connection", (socket) => {
  socket.join("some room");
});

And then simply use to or in (they are the same) when broadcasting or emitting:

io.to("some room").emit("some event");

3. how do you leave a room?

To leave a channel you call leave in the same fashion as join.

Namespaces

1. What is a Namespace and what does it allow you to do?

A Namespace is a communication channel that allows you to split the logic of your application over a single shared connection (also called “multiplexing”).

2. Each namespace potentially has its own what? (hint: 3 things)

event handlers, rooms, and middlewares

3. Discuss a possible use case for separate namespaces

you want to create a special namespace that only authorized users have access to, so the logic related to those users is separated from the rest of the application