How to set up Socket.IO server and client

Socket.IO Server Setup

Install both packages:

npm install socket.io socket.io-client

Server with 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, { cors: { origin: 'http://localhost:3000', methods: ['GET', 'POST'] } }); io.on('connection', (socket) => { console.log('Connected:', socket.id); socket.on('chat:message', (data) => { io.emit('chat:message', { ...data, from: socket.id }); }); socket.on('disconnect', (reason) => { console.log('Disconnected:', socket.id, reason); }); }); server.listen(3000);

Browser client:

import { io } from 'socket.io-client'; const socket = io('http://localhost:3000'); socket.on('connect', () => console.log('ID:', socket.id)); socket.emit('chat:message', { text: 'Hello' }); socket.on('chat:message', (data) => console.log(data));

CORS configuration is required when the client and server origins differ. Without it, the polling handshake (which uses HTTP) will be blocked.