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# WebSocket Setup > Implement WebSocket server with rooms You are a Node.js backend engineer. The user wants to implement a WebSocket server with room-based communication using Socket.IO. ## What to check first - Verify Node.js is installed: `node --version` (v14+) - Check if Socket.IO is in package.json: `npm list socket.io` - Confirm an HTTP server package exists: `npm list express` or `npm list http` ## Steps 1. Install Socket.IO: `npm install socket.io` (also need `npm install express` for the HTTP server) 2. Create an Express server and attach Socket.IO to it using `http.createServer(app)` 3. Initialize Socket.IO with the server instance: `const io = require('socket.io')(httpServer)` 4. Listen for the `connection` event on the io instance to handle new socket connections 5. Inside the connection handler, use `socket.on('join', callback)` to handle room join requests with the room name parameter 6. Use `socket.join(roomName)` to add the socket to a room 7. Broadcast messages to a specific room using `io.to(roomName).emit(eventName, data)` 8. Handle disconnection with `socket.on('disconnect')` and optionally use `socket.leave(roomName)` before cleanup ## Code ```javascript const express = require('express'); const http = require('http'); const socketIO = require('socket.io'); const app = express(); const server = http.createServer(app); const io = socketIO(server, { cors: { origin: '*', methods: ['GET', 'POST'] } }); const PORT = process.env.PORT || 3000; // Track room members const rooms = {}; io.on('connection', (socket) => { console.log(`User connected: ${socket.id}`); // Handle joining a room socket.on('join', (roomName, userName) => { socket.join(roomName); socket.currentRoom = roomName; socket.userName = userName; if (!rooms[roomName]) { rooms[roomName] = []; } rooms[roomName].push({ id: socket.id, name: userName }); // Notify others in the room io.to(roomName).emit('user-joined', { userName: userName, userId: socket.id, totalUsers: rooms[roomName].length }); // Send room state to the joining user socket.emit('room-state', { members: rooms[roomName], roomName: roomName }); }); // Handle messages in a room socket.on('message', (msg) => { if (socket.currentRoom) { io.to(socket.currentRoom).emit('new-message', { userId: socket.id, userName: socket.userName, text: msg, timestamp: new Date ``` *Note: this example was truncated in the source. See [the GitHub repo](https://github.com/Samarth0211/claude-skills-hub) for the latest full version.* ## Common Pitfalls - Treating this skill as a one-shot solution — most workflows need iteration and verification - Skipping the verification steps — you don't know it worked until you measure - Applying this skill without understanding the underlying problem — read the related docs first ## When NOT to Use This Skill - When a simpler manual approach would take less than 10 minutes - On critical production systems without testing in staging first - When you don't have permission or authorization to make these changes ## How to Verify It Worked - Run the verification steps documented above - Compare the output against your expected baseline - Check logs for any warnings or errors — silent failures are the worst kind ## Production Considerations - Test in staging before deploying to production - Have a rollback plan — every change should be reversible - Monitor the affected systems for at least 24 hours after the change --- *From [CLSkills.in](https://clskills.in/browse) — 2,300+ free Claude Code skills*