Broadcasting messages in NestJS - Mini Project: Build & Apply

Broadcasting messages

📖 Scenario: You are building a simple NestJS application that can send a broadcast message to multiple connected clients using WebSockets.This is useful in real-time apps like chat rooms or live notifications.

🎯 Goal: Create a NestJS WebSocket gateway that can broadcast a message to all connected clients.

📋 What You'll Learn

Create a WebSocket gateway class named AppGateway

Add a method called broadcastMessage that sends a message to all clients

Use the @WebSocketServer() decorator to access the server instance

Broadcast a string message 'Hello everyone!' to all connected clients

💡 Why This Matters

🌍 Real World

Broadcasting messages is essential in real-time applications like chat apps, live notifications, and multiplayer games to keep all users updated instantly.

💼 Career

Understanding WebSocket gateways and broadcasting in NestJS is valuable for backend developers working on scalable real-time systems.

1

Create the WebSocket gateway class

Create a class called AppGateway and decorate it with @WebSocketGateway() from @nestjs/websockets. Import the decorator correctly.

NestJS

import { WebSocketGateway } from '@nestjs/websockets';

// Your code here

Need a hint?

Use @WebSocketGateway() above the class declaration.

2

Add the WebSocket server property

Inside the AppGateway class, add a property called server decorated with @WebSocketServer() imported from @nestjs/websockets. This will hold the WebSocket server instance.

NestJS

import { WebSocketGateway, WebSocketServer } from '@nestjs/websockets';

@WebSocketGateway()
export class AppGateway {
  // Your code here
}

Need a hint?

Import WebSocketServer and add @WebSocketServer() server: Server; inside the class.

3

Add the broadcastMessage method

Add a method called broadcastMessage inside AppGateway that calls this.server.emit with event name 'broadcast' and message 'Hello everyone!'.

NestJS

import { WebSocketGateway, WebSocketServer } from '@nestjs/websockets';
import { Server } from 'socket.io';

@WebSocketGateway()
export class AppGateway {
  @WebSocketServer()
  server: Server;

  // Your code here
}

Need a hint?

Define broadcastMessage() that uses this.server.emit to send the message.

4

Call broadcastMessage in the constructor

Add a constructor to AppGateway and call this.broadcastMessage() inside it to send the broadcast message when the gateway starts.

NestJS

import { WebSocketGateway, WebSocketServer } from '@nestjs/websockets';
import { Server } from 'socket.io';

@WebSocketGateway()
export class AppGateway {
  @WebSocketServer()
  server: Server;

  broadcastMessage() {
    this.server.emit('broadcast', 'Hello everyone!');
  }

  // Your code here
}

Need a hint?

Add a constructor() method and call this.broadcastMessage() inside it.