@nestjs/event-emitter

What is @nestjs/event-emitter?

@nestjs/event-emitter is a module for NestJS that provides an event-driven architecture. It allows you to emit and listen to events within your NestJS application, making it easier to decouple different parts of your application and improve maintainability.

What are @nestjs/event-emitter's main functionalities?

Event Emission

This feature allows you to emit events from any part of your application. In this example, the `MyService` class emits an event named 'my.event' with some data.

const { Injectable } = require('@nestjs/common');
const { EventEmitter2 } = require('@nestjs/event-emitter');

@Injectable()
class MyService {
  constructor(private eventEmitter: EventEmitter2) {}

  triggerEvent() {
    this.eventEmitter.emit('my.event', { data: 'some data' });
  }
}

Event Listener

This feature allows you to listen to events emitted within your application. In this example, the `MyListener` class listens for the 'my.event' event and handles it by logging the payload.

const { Injectable } = require('@nestjs/common');
const { OnEvent } = require('@nestjs/event-emitter');

@Injectable()
class MyListener {
  @OnEvent('my.event')
  handleMyEvent(payload) {
    console.log('Event received:', payload);
  }
}

Event Payload Validation

This feature allows you to validate the payload of events. In this example, the `MyEventPayload` class uses class-validator to ensure that the `data` property is a string. The `MyListener` class listens for the 'my.event' event and handles it asynchronously.

const { Injectable } = require('@nestjs/common');
const { OnEvent } = require('@nestjs/event-emitter');
const { IsString } = require('class-validator');

class MyEventPayload {
  @IsString()
  data;
}

@Injectable()
class MyListener {
  @OnEvent('my.event', { async: true })
  async handleMyEvent(payload: MyEventPayload) {
    console.log('Validated event received:', payload);
  }
}

Other packages similar to @nestjs/event-emitter

eventemitter2

EventEmitter2 is a Node.js module that extends the EventEmitter class to provide additional features such as namespaced events, wildcards, and more. It is more general-purpose compared to @nestjs/event-emitter, which is specifically designed for NestJS applications.

rxjs

RxJS is a library for reactive programming using Observables. It provides powerful operators for event handling, transformation, and composition. While RxJS is more complex and feature-rich, @nestjs/event-emitter offers a simpler and more straightforward API for event-driven architecture in NestJS.

mitt

Mitt is a tiny (~200 bytes) functional event emitter. It is extremely lightweight and easy to use, but lacks some of the advanced features provided by @nestjs/event-emitter, such as integration with NestJS's dependency injection system.

README

A progressive Node.js framework for building efficient and scalable server-side applications.

Description

Events module for Nest built on top of the eventemitter2 package.

Installation

$ npm i --save @nestjs/event-emitter

Quick Start

Overview & Tutorial

Support

Nest is an MIT-licensed open source project. It can grow thanks to the sponsors and support by the amazing backers. If you'd like to join them, please read more here.

Stay in touch

• Author - Kamil Myśliwiec
• Website - https://nestjs.com
• Twitter - @nestframework

License

Nest is MIT licensed.