How do I handle Socket.io events in React?
In useEffect, emit join events with socket.emit(), listen for events with socket.on(), and return a cleanup function that calls socket.off() for each event. This prevents duplicate listeners when the component re-renders or unmounts.
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More FAQs in Setting Up Socket.io with Express in Node.js Server and Client Configuration
Create an HTTP server from the Express app (http.createServer(app)), initialize socketio with CORS config (socketio(server, { cors: { origin, credentials: true } })), add authentication middleware with io.use(), handle connection events with io.on('connection', ...), and listen on the HTTP server (not the Express app).
Use io.use() middleware: read the token from socket.handshake.auth.token, verify with jwt.verify(), find the user, and attach to socket.user. If verification fails, call next(new Error('Authentication failed')). The client passes the token in the auth option when connecting.
Install socket.io-client, import { io } from 'socket.io-client', connect with io(url, { withCredentials: true, auth: { token } }), listen with socket.on('event', callback), and emit with socket.emit('event', data). Clean up listeners in useEffect return with socket.off().
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