app.controller.ts

import { Body, Controller, Post } from '@nestjs/common';
import { AppService } from './app.service';
import { CommentDTO } from './comment.interfaces';

@Controller()
export class AppController {
  constructor(private readonly appService: AppService) {}

  @Post()
  addComment(@Body() data: CommentDTO) {
    return this.appService.addComment(data);
  }
}

app.module.ts

import { BullModule } from '@nestjs/bull';
import { Module } from '@nestjs/common';
import { EventEmitterModule } from '@nestjs/event-emitter';

import { AppController } from './app.controller';
import { AppService } from './app.service';

@Module({
  imports: [
    BullModule.registerQueue({
      name: 'emails',
      redis: {
        host: 'localhost',
        port: 7003,
      },
    }),
    EventEmitterModule.forRoot({}),
  ],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

app.service.ts

import { Injectable } from '@nestjs/common';
import { EventEmitter2 } from '@nestjs/event-emitter';
import { CommentEvents, NewCommentEvent } from './comment.events';

import { CommentDTO } from './comment.interfaces';

@Injectable()
export class AppService {
  constructor(private readonly eventEmitter: EventEmitter2) {}
  addComment(data: CommentDTO) {
    // First we validate and save our comment inside a database
    // We'll skip that part inside this exemple.

    // Then we emit the event that a new comment has been added
    // note that we use emitAsync to avoid blocking the thread
    this.eventEmitter.emitAsync(
      CommentEvents.NewComment,
      new NewCommentEvent(data),
    );

    // Then our work is done, we return here.
    return {
      done: true,
    };
  }
}

comment.events.ts

import { CommentDTO } from './comment.interfaces';

export enum CommentEvents {
  NewComment = 'comments.new',
}

export class NewCommentEvent {
  constructor(public comment: CommentDTO) {}
}

comment.interfaces.ts

export type CommentDTO = {
  text: string;
};