Type Safe, contract-driven event emitter module for a NestJS application.

Uses zod object defintions to create typesafe event listeners and emitter, with automatic validation of args.

Features

• End-to-end type safe wrapper for eventemitter2
• Wild card events
• Enforce events have a listener via contract.required(<event>, <schema>)
• Optional event listeners via contract.optional(<event>, <schema>)

Installation

npm i eventemitter2 nestjs-typed-events

Limitations

• You can have multiple event listeners on one class only if the events have the same args signature.

Example

1. Register in app.module

import { EventContractBuilder, EventEmitterModule } from 'nestjs-typed-events';

const contract = EventContractBuilder.create()
  .required(
    'test.event',
    z.object({
      foo: z.string(),
    }),
  )
  .optional('optional.event', z.string())
  .build();

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

2. Register your event listener

import { Injectable } from '@nestjs/common';
import {
  EventListenerDecoratorFactory,
  ContractEvent,
} from 'nestjs-typed-events';

const ContractEvent = EventListenerDecoratorFactory(contract);

@Injectable()
@ContractEvent('test.event')
export class TestWatcher {
  async handle(args: ContractEvent<typeof contract['test.event']>) {}
}

3. Profit