Categorizing Sockets and Broadcasting to Rooms with Socket.IO

2 min read.

The idea and execution of creating ‘Rooms’ with Socket.IO and only emitting an event to users in that specific room is documented as overly complex, but it doesn’t have to be. This process is actually rather simple if you read the right material. For, Coder Combat, I needed to use SocketIO’s Rooms to create the one on one game play that I desired. This post will hopefully get you started on the right path of using Socket.IO rooms.

First, to have a specific Socket join a room, on ‘Connection’, do socket.join(‘roomName’). Then that specific Sockets room can be accessed and seen by doing io.sockets.clients(‘roomName’). Although convenient, I actually found that keeping track of rooms in this matter was frustrating because there are a lot more methods and properties that each socket had so it crowded what I actually cared about, which was the room. To fix this I just created the following variables.

var room;
var playerCountInRoom = 0;
var roomCount = 0;
var roomList = {};

First off whenever a new user would connect, I would give that Socket it’s own property of ‘room’ (socket[‘room’] = room) with room being roomCount.toString(). This would ensure that every socket was then put in the appropriate room.

As you can see, I need a roomCount to be able to increment every time the room is full (or room % 2 === 0), and I had a roomList object that I would add the users to whenever a new user would connect. Now, I had this convenient object that basically mirrors the overly complex Object that Socket.IO kept for me. Once you actually have the desired amount of users in a room, emitting events to only those users is simple. Here’s the run down.

io.sockets.in(‘roomName’).emit(); This emits whatever you want to ALL users who are in the room ‘roomName’.

socket.broadcast.to(‘roomName’).emit() This emits whatever you want to every user in ‘roomName’ EXCEPT FOR the sender.

Although you probably won’t use it, io.sockets.emit() emits an event to all sockets connected to the server.

Last but not least socket.broadcast.emit() emits whatever to all sockets connected to the server except for the socket sending the request.

That’s really it. You just add a room property to every socket, create a roomList object to keep track of which rooms every is in, then you broadcast and event to only the room you want to receive that event.

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