Module Internals

Preview — 3 of 10 questions

During bootstrap, what does Nest's DependenciesScanner/compiler do before any provider is instantiated?

javascript

// Conceptual: scan populates the container before instantiation
// container.addModule(metatype, scope)
// container.addProvider(provider, token)  → creates InstanceWrapper
// then InstanceLoader.createInstancesOfDependencies()

AIt executes every controller method once to warm caches

BIt recursively scans modules and their metadata to build a graph of modules, providers, controllers, and their relationships, registering them in the NestContainer

CIt compiles TypeScript to JavaScript on the fly

DIt opens database connections eagerly

What is the key difference between moduleRef.get() and moduleRef.resolve()?

javascript

@Injectable()
export class Service {
  constructor(private moduleRef: ModuleRef) {}

  async work(): Promise<void> {
    const singleton = this.moduleRef.get(ConfigService); // sync, shared
    const scoped = await this.moduleRef.resolve(RequestScopedSvc); // async, fresh
  }
}

Aget() is async; resolve() is sync

BThey are identical aliases

Cget() retrieves a singleton (DEFAULT-scoped) instance synchronously; resolve() is async and returns a fresh instance for scoped (REQUEST/TRANSIENT) providers, optionally tied to a ContextId

Dresolve() only works for controllers

What role does the MODULE_PATH metadata serve in Nest?

javascript

import { RouterModule } from '@nestjs/core';

@Module({
  imports: [
    AdminModule,
    RouterModule.register([{ path: 'admin', module: AdminModule }]),
  ],
})
export class AppModule {}

AIt can prefix routes for all controllers within a module (module-level route path), and is part of how Nest associates modules during scanning

BIt sets the file system path for hot reload

CIt defines the npm package name

DIt is the database schema name

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