akwodkiewicz / nestjs-aop

A library that makes aspect-oriented programming easier

@nestjs-architects/aop

If you don't know what AOP is check this out

Usage

$ npm i @nestjs-architects/aop

Create your own advice (additional piece of code executed along with the original method)

import { AdviceProvider } from '@nestjs-architects/aop';

interface LoggingOptions {
  format: 'JSON' | 'TEXT';
}

class LoggingAdvice implements AdviceProvider {
  async attach(
    originalMethod: Function,
    args: unknown[],
    options: LoggingOptions
  ): Promise<unknown> {
    console.log('Before...');
    const result = await originalMethod(...args);
    console.log('After...');
    return result;
  }
}

Define a decorator and attach it to your methods

import { SetMetadata } from '@nestjs/common';

const LOGGING_KEY = 'LOGGING';
export const Logging = (options: LoggingOptions) =>
  SetMetadata(LOGGING_KEY, options);

@Injectable()
export class AppService {
  @Logging()
  getHello(): string {
    console.log('Initial method called');
    return 'Hello World!';
  }
}

Register both as your own aspect

import { AopModule, AspectsRegistry } from '@nestjs-architects/aop';
import { Module } from '@nestjs/common';

@Module({
  imports: [AopModule],
  providers: [LoggingAdvice],
})
export class LoggingModule {
  constructor(
    private readonly registry: AspectsRegistry,
    private readonly loggingAdvice: LoggingAdvice
  ) {
    this.registry.addAspect(LOGGING_KEY, this.loggingAdvice);
  }
}

Profit

Now, every time the decoreted method is called the additional code provided by you is executed too.

Learn more

Aspect-oriented programming with NestJS