1. Install Required Dependencies

Install the WebSocket package for NestJS:

npm install @nestjs/websockets @nestjs/platform-socket.io

2. Create a Gateway

Create a WebSocket gateway in your NestJS application.

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

@WebSocketGateway({ cors: true }) // Enable CORS if Angular runs on a different domain
export class NotificationsGateway {
  @WebSocketServer()
  server: Server;

  // Handle new connections
  handleConnection(client: Socket) {
    console.log(`Client connected: ${client.id}`);
  }

  // Handle disconnections
  handleDisconnect(client: Socket) {
    console.log(`Client disconnected: ${client.id}`);
  }

  // Listen for custom events
  @SubscribeMessage('sendNotification')
  handleNotification(
    @MessageBody() data: { message: string },
    @ConnectedSocket() client: Socket,
  ) {
    console.log(`Received message: ${data.message}`);
    // Broadcast to all clients
    this.server.emit('receiveNotification', data);
  }
}

3. Add the Gateway to a Module

Register the gateway in a module (e.g., AppModule).

import { Module } from '@nestjs/common';
import { NotificationsGateway } from './notifications.gateway';

@Module({
  providers: [NotificationsGateway],
})
export class AppModule {}