WebSockets & Real-time Communication

WebSockets provide a persistent connection between a client and a server that both parties can use to start sending data at any time. This is essential for features like chat applications, live notifications, and real-time dashboards.

1. Why WebSockets?

Unlike HTTP, which is request-response based, WebSockets allow for:

Full-Duplex Communication: Both server and client can send messages simultaneously.
Low Latency: Once the connection is established, data can flow without the overhead of HTTP headers for every message.

2. Using Socket.io

Socket.io is the most popular library for WebSockets in Node.js. It provides a simple API and fallback options for older browsers.

Installation

npm install socket.io

Basic Server Setup (with Express)

import express from 'express';
import { createServer } from 'http';
import { Server } from 'socket.io';

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

io.on('connection', (socket) => {
  console.log('A user connected');

  socket.on('chat message', (msg) => {
    console.log('Message: ' + msg);
    io.emit('chat message', msg); // Broadcast to all users
  });

  socket.on('disconnect', () => {
    console.log('User disconnected');
  });
});

server.listen(3000, () => {
  console.log('Listening on *:3000');
});

3. Client-Side Implementation

const socket = io(); // Connects to the server

// Sending a message
socket.emit('chat message', 'Hello Server!');

// Receiving a message
socket.on('chat message', (msg) => {
  console.log('New message: ' + msg);
});

[!TIP] Use Rooms in Socket.io to group users together (e.g., chat rooms, specific notification channels).