WebSocket in Node.js: ws Library for Real-Time

Library ws: WebSocket for Node.js

The ws library is a simple, fast, and thoroughly tested implementation of the WebSocket protocol for Node.js. It is the de facto standard for creating real-time applications (chats, online games, notifications, collaborative editing) on the server-side JavaScript. Unlike the built-in http module, ws provides full bidirectional communication between client and server without constant HTTP requests.

Key Features

• Full support for RFC 6455 protocol — works with all modern browsers.
• High performance — minimal memory consumption and low latency.
• Simple API — create a server and client in a few lines of code.
• Extension support — data compression (permessage-deflate).
• Integration with HTTP server — can share a port with Express or other frameworks.
• Automatic reconnection — built-in mechanisms for the client.

Installation

Installation via npm:

npm install ws

After installation, the library is ready to use.

Creating a WebSocket Server

Let's create a simple server that accepts connections and sends a welcome message:

const WebSocket = require('ws');

const wss = new WebSocket.Server({ port: 8080 });

wss.on('connection', function connection(ws) {  console.log('New client connected');

  // Send a message to the client  ws.send('Welcome to the WebSocket server!');

  // Handle incoming messages  ws.on('message', function incoming(message) {    console.log('Received: %s', message);    // Send back (echo)    ws.send('Echo: ' + message);  });

  // Handle connection close  ws.on('close', function() {    console.log('Client disconnected');  });});

console.log('WebSocket server started on ws://localhost:8080');

Creating a WebSocket Client

The client connects to the server, sends a message, and receives a response:

const WebSocket = require('ws');

const ws = new WebSocket('ws://localhost:8080');

ws.on('open', function open() {  console.log('Connection established');  ws.send('Hello, server!');});

ws.on('message', function incoming(data) {  console.log('Response from server: %s', data);  ws.close();});

ws.on('close', function() {  console.log('Connection closed');});

ws.on('error', function error(err) {  console.error('Error:', err.message);});

Working with JSON and Multiple Clients

A real-world example — a chat server that broadcasts messages to all connected clients:

const WebSocket = require('ws');

const wss = new WebSocket.Server({ port: 8080 });

wss.on('connection', function connection(ws, req) {  console.log('Client connected. Total clients:', wss.clients.size);

  ws.on('message', function incoming(message) {    // Parse JSON    let data;    try {      data = JSON.parse(message);    } catch (e) {      ws.send(JSON.stringify({ error: 'Invalid JSON' }));      return;    }

    // Broadcast to everyone except the sender    wss.clients.forEach(function each(client) {      if (client !== ws && client.readyState === WebSocket.OPEN) {        client.send(JSON.stringify({          username: data.username,          text: data.text,          timestamp: Date.now()        }));      }    });  });

  ws.send(JSON.stringify({ system: 'Welcome to the chat!' }));});

The client can send JSON:

ws.send(JSON.stringify({ username: 'Alice', text: 'Hello everyone!' }));

Integration with HTTP Server