WebSocket — Explained with Examples

WebSocket is a full-duplex communication protocol that provides persistent, bidirectional channels between client and server over a single TCP connection.

WebSocket (defined in RFC 6455) enables real-time, event-driven communication where both client and server can send messages at any time. Unlike HTTP’s request-response model, WebSocket keeps the connection open.

How WebSocket Differs from HTTP

HTTP is like sending a letter and waiting for a reply each time. WebSocket is like making a phone call — once connected, both sides can talk freely without the overhead of establishing a new connection for each message.

Client → Server: HTTP Upgrade request (handshake)
Server → Client: 101 Switching Protocols
  ─── connection established ───
Client → Server: Message (any time)
Server → Client: Message (any time)
Client → Client: Message (any time)
  ─── connection stays open ───

Example: WebSocket Chat Server

const WebSocket = require('ws');
const server = new WebSocket.Server({ port: 8080 });

server.on('connection', (ws) => {
  console.log('Client connected');

  ws.on('message', (message) => {
    console.log(`Received: ${message}`);
    // Broadcast to all connected clients
    server.clients.forEach(client => {
      if (client.readyState === WebSocket.OPEN) {
        client.send(`Server: ${message}`);
      }
    });
  });

  ws.send('Welcome to the chat!');
});

// Client-side JavaScript
const ws = new WebSocket('ws://localhost:8080');

ws.onopen = () => {
  ws.send('Hello server!');
};

ws.onmessage = (event) => {
  console.log('Server says:', event.data);
};

Expected output: Client receives “Welcome to the chat!” and “Server: Hello server!”.

Real-World Analogy

HTTP is like sending postcards — you write, mail, and wait for a response. WebSocket is like a two-way radio — you press to talk, release to listen, and both sides can transmit over the same channel without re-establishing contact each time.

Related Terms

SSE, REST, gRPC, HTTP, API Gateway

Related Tutorial

WebSocket Protocol — Complete Guide