**Course Title:** Mastering NestJS: Building Scalable Server-Side Applications **Section Title:** WebSockets and Real-Time Applications **Topic:** Implementing real-time features in NestJS applications **Overview** In this topic, we will explore how to implement real-time features in NestJS applications using WebSockets. WebSockets provide a bi-directional communication channel between a client and a server, allowing for real-time updates and interactions. We will cover the basics of WebSockets, how to use them in NestJS, and provide examples of real-world applications. **What are WebSockets?** WebSockets are a protocol that enables bidirectional, real-time communication between a client (usually a web browser) and a server over the web. They allow for efficient, low-latency communication, making them ideal for applications that require real-time updates, such as live updates, live chat, and gaming. **How do WebSockets work?** Here's a high-level overview of how WebSockets work: 1. The client (web browser) establishes a connection to the server using the WebSocket protocol. 2. The server accepts the connection and establishes a WebSocket connection. 3. The client and server can now send and receive messages to each other in real-time. **Implementing WebSockets in NestJS** To implement WebSockets in NestJS, we will use the `@nestjs/websockets` package. This package provides a simple way to create WebSocket servers and clients. **Step 1: Install the `@nestjs/websockets` package** To start, we need to install the `@nestjs/websockets` package. Run the following command in your terminal: ```bash npm install @nestjs/websockets ``` **Step 2: Create a WebSocket server** Next, we need to create a WebSocket server. We can do this by creating a new class that extends the `WsServer` class from the `@nestjs/websockets` package. ```typescript import { WebSocketServer } from '@nestjs/websockets'; import { Server } from 'ws'; export class AppService { constructor(private readonly app: NestFactory) {} async createServer() { const server = new Server({ cors: { origin: '*', methods: ['GET', 'POST'], }, }); const wss = new WebSocketServer(server); wss.on('connection', (ws) => { console.log('Client connected'); ws.on('message', (message) => { console.log(`Received message => ${message}`); }); ws.on('close', () => { console.log('Client disconnected'); }); }); return server; } } ``` **Step 3: Create a WebSocket client** To create a WebSocket client, we can use the `WebSocket` class from the `ws` package. ```typescript import { WebSocket } from 'ws'; const ws = new WebSocket('ws://localhost:3000'); ws.on('open', () => { console.log('Connected to the server'); ws.send('Hello from client'); }); ws.on('message', (message) => { console.log(`Received message => ${message}`); }); ws.on('close', () => { console.log('Disconnected from the server'); }); ``` **Real-world applications of WebSockets** WebSockets have a wide range of applications in real-world scenarios, including: * Live updates: WebSockets can be used to provide live updates to users, such as stock prices, sports scores, or news. * Live chat: WebSockets can be used to create live chat applications, where users can communicate with each other in real-time. * Gaming: WebSockets can be used to create real-time gaming applications, where users can interact with each other in real-time. * Collaborative editing: WebSockets can be used to create collaborative editing applications, where multiple users can edit a document simultaneously. **Conclusion** In this topic, we have covered the basics of WebSockets and how to implement them in NestJS applications. We have also discussed the real-world applications of WebSockets and how they can be used to create real-time applications. **What's next?** In the next topic, we will cover how to use the Socket.IO library with NestJS to create real-time applications. **Leave a comment or ask for help** If you have any questions or need help with implementing WebSockets in your NestJS application, please leave a comment below. **External resources** For more information on WebSockets and how to implement them in NestJS, please refer to the following resources: * [WebSockets documentation](https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API) * [NestJS WebSocket documentation](https://docs.nestjs.com/techniques/websockets) * [Socket.IO documentation](https://socket.io/docs/)