Broadcasting to rooms in Express - Mini Project: Build & Apply

Broadcasting to rooms

📖 Scenario: You are building a simple chat server using Express and Socket.IO. You want to organize users into different chat rooms so messages can be sent only to users in the same room.

🎯 Goal: Create an Express server with Socket.IO that allows clients to join specific rooms and broadcast messages only to users in those rooms.

📋 What You'll Learn

Create an Express server with Socket.IO

Set up a Socket.IO connection handler

Allow clients to join a room using socket.join(roomName)

Broadcast messages to all clients in a specific room using io.to(roomName).emit()

💡 Why This Matters

🌍 Real World

Chat applications often use rooms to separate conversations by topic or group, making communication organized and efficient.

💼 Career

Understanding how to broadcast messages to rooms is essential for building real-time collaborative apps, chat systems, and multiplayer games.

1

Set up Express server and Socket.IO

Create an Express server and attach Socket.IO to it. Create a variable called app for Express and server for the HTTP server. Then create io by passing server to Socket.IO.

Express

const express = require('express');
const http = require('http');
const { Server } = require('socket.io');

// Your code here

Need a hint?

Use express() to create the app, then http.createServer(app) for the server, and finally new Server(server) for Socket.IO.

2

Add connection event handler

Add a connection event handler on io using io.on('connection', socket => { ... }). Inside the handler, create a variable called socket representing the connected client.

Express

const express = require('express');
const http = require('http');
const { Server } = require('socket.io');

const app = express();
const server = http.createServer(app);
const io = new Server(server);

// Your code here

Need a hint?

Use io.on('connection', socket => { ... }) to handle new clients.

3

Join clients to rooms

Inside the connection handler, listen for a 'joinRoom' event on socket. When received, call socket.join(roomName) where roomName is the event data.

Express

const express = require('express');
const http = require('http');
const { Server } = require('socket.io');

const app = express();
const server = http.createServer(app);
const io = new Server(server);

io.on('connection', socket => {
  // Your code here
});

Need a hint?

Use socket.on('joinRoom', roomName => { socket.join(roomName) }) to add clients to rooms.

4

Broadcast messages to rooms

Inside the connection handler, listen for a 'message' event on socket with data containing roomName and msg. Use io.to(roomName).emit('message', msg) to send the message to all clients in that room.

Express

const express = require('express');
const http = require('http');
const { Server } = require('socket.io');

const app = express();
const server = http.createServer(app);
const io = new Server(server);

io.on('connection', socket => {
  socket.on('joinRoom', roomName => {
    socket.join(roomName);
  });
  // Your code here
});

Need a hint?

Listen for 'message' events with { roomName, msg } and broadcast using io.to(roomName).emit('message', msg).