@nestjs-architects/aop

Profit

This package will help you make your services clean and focused on the feature. Many non-functional requirements can be easily added using Aspect-Oriented Programming.

Learn more

Aspect-oriented programming with NestJS

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.

Adding aspects to services created manually

There are cases when you would like to create a new service dynamically, not just inject it.

For such services you can use AspectsApplier.

import { AspectsApplier } from '@nestjs-architects/aop';
import { Injectable } from '@nestjs/common';

export class Speaker {
  @Logging()
  speak() {
    console.log('I am not a singleton');
  }
}

@Injectable()
export class AppService {
  constructor(private readonly aspectsApplier: AspectsApplier) {}
  speak() {
    const service = new Speaker();
    this.aspectsApplier.applyToProvider(service);
    service.speak();
  }
}