Effects NestJS Module

A small NestJS helper that wraps controller handlers with an interceptor and emits an event via @nestjs/event-emitter when the request completes successfully. This makes it easy to run side effects after REST create/update/delete operations without blocking the main flow.

Installation

npm install @nolawnchairs/effects-nestjs

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Peer Dependencies

This package requires the following peer dependencies to be installed:

• @nestjs/common
• @nestjs/core
• @nestjs/event-emitter
• reflect-metadata
• rxjs

Quick Start

Import the module once in your application:

import { Module } from '@nestjs/common'
import { EffectsModule } from '@nolawnchairs/effects-nestjs'

@Module({
  imports: [EffectsModule.forRoot()],
})
export class AppModule {}

Decorate controller methods with @Dispatch(...) to emit events on successful completion:

import { Body, Controller, Delete, Param, Post, Put } from '@nestjs/common'
import { Dispatch } from '@nolawnchairs/effects-nestjs'

@Controller('cats')
export class CatsController {
  @Post()
  @Dispatch('cats.created')
  create(@Body() body: { name: string }) {
    return { id: 'cat_123', name: body.name }
  }

  @Put(':id')
  @Dispatch('cats.updated')
  update(@Param('id') id: string, @Body() body: { name: string }) {
    return { id, name: body.name }
  }

  @Delete(':id')
  @Dispatch('cats.deleted')
  remove(@Param('id') id: string) {
    return { id }
  }
}

Each @Dispatch() call automatically applies EffectsInterceptor via @UseInterceptors(), so you do not need to wire the interceptor yourself.

Listening for Events

Use the standard @nestjs/event-emitter API to subscribe:

import { Injectable } from '@nestjs/common'
import { OnEvent } from '@nestjs/event-emitter'
import { DispatchedEffectEvent } from '@nolawnchairs/effects-nestjs'

@Injectable()
export class CatsListener {
  @OnEvent('cats.*')
  handleCatEvent(event: DispatchedEffectEvent<{ id: string; name?: string }>) {
    console.log('Cat event:', event.value)
  }
}

Event Payload

The event payload is an instance of DispatchedEffectEvent<T, R> and contains:

• value - The return value of the decorated method, typed as T.
• request - The request object from the execution context, typed as R (e.g., Express).

Notes

• Events are emitted only after a handler completes successfully.
• Errors thrown by the handler do not emit an event.