Runtim

Dependencies

Say we are making a simple app with an HTTP route (to provide post data). Our app consists of a controller (HTTP endpoint), a provider (logic to access the data) and main module.

1. In our controller, we declare the PostsService as a dependency in the constructor

• PostsService is available to be injected in the first place because it has the @Injectable decorator.

2. In PostsModule, the class PostsService is associated with a token also called PostsService (providers key)

• the token is used by the Nestjs runtime to request an instance of a class (most often by the same name. This is configurable, and is what we are doing when we provide the long-form object with keys provide and useFactory/useValue, useClass)

@Module({
  controllers: [PostsController],
  providers: [PostsService],
})