Feature modules in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the feature module into the root module.

NestJS

import { Module } from '@nestjs/common';
import { UsersModule } from './users/users.module';

@Module({
  imports: [[1]],
})
export class AppModule {}

Drag options to blanks, or click blank then click option'

AUsersModules

BUserModule

CusersModule

DUsersModule

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect casing like 'usersModule' or plural forms.

Misspelling the module name.

The feature module UsersModule must be imported exactly by its exported class name.

2fill in blank

medium

Complete the code to declare a controller inside a feature module.

NestJS

import { Module } from '@nestjs/common';
import { UsersController } from './users.controller';

@Module({
  controllers: [[1]],
})
export class UsersModule {}

Drag options to blanks, or click blank then click option'

AUsersController

BusersController

CUserController

DUsersControllers

Attempts:

3 left

💡 Hint

Common Mistakes

Using singular form 'UserController' when the file exports 'UsersController'.

Incorrect casing like 'usersController'.

The controller must be declared by its exact exported class name UsersController.

3fill in blank

hard

Fix the error in the feature module by completing the providers array.

NestJS

import { Module } from '@nestjs/common';
import { UsersService } from './users.service';

@Module({
  providers: [[1]],
})
export class UsersModule {}

Drag options to blanks, or click blank then click option'

AusersService

BUsersService

CUserService

DUsersServices

Attempts:

3 left

💡 Hint

Common Mistakes

Using singular 'UserService' when the service is named 'UsersService'.

Incorrect casing or pluralization.

The provider must be the exact exported class name UsersService to register the service correctly.

4fill in blank

hard

Fill both blanks to export the service and import the feature module correctly.

NestJS

import { Module } from '@nestjs/common';
import { UsersService } from './users.service';

@Module({
  providers: [[1]],
  exports: [[2]],
})
export class UsersModule {}

Drag options to blanks, or click blank then click option'

AUsersService

BUserService

CUsersModule

DUsersServices

Attempts:

3 left

💡 Hint

Common Mistakes

Exporting the module instead of the service.

Using incorrect service names or casing.

The service UsersService must be both provided and exported to be used in other modules.

5fill in blank

hard

Fill all three blanks to create a feature module with controller, service, and export the service.

NestJS

import { Module } from '@nestjs/common';
import { UsersController } from './users.controller';
import { UsersService } from './users.service';

@Module({
  controllers: [[1]],
  providers: [[2]],
  exports: [[3]],
})
export class UsersModule {}

Drag options to blanks, or click blank then click option'

AUsersController

BUsersService

DUserController

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up controller and service names.

Not exporting the service when needed.

The controller and service must be declared correctly, and the service exported for use in other modules.

Practice

1. What is the main purpose of a feature module in NestJS?

easy

A. To manage HTTP requests without controllers

B. To group related controllers and services for better organization

C. To replace the main application module

D. To handle database connections directly

Solution

1. Step 1: Understand the role of feature modules

   Feature modules group related parts of the app like controllers and services to keep code organized.

2. Step 2: Compare options with this role

   Only To group related controllers and services for better organization describes grouping related controllers and services, which matches the purpose.

3. Final Answer:

   To group related controllers and services for better organization -> Option B

4. Quick Check:

   Feature modules organize code = D [OK]

Hint: Feature modules group related parts of your app [OK]

Common Mistakes:

• Thinking feature modules handle database connections directly
• Confusing feature modules with the main app module
• Assuming feature modules replace controllers

2. Which of the following is the correct way to define a feature module in NestJS?

easy

A. @Controller({}) export class FeatureModule {}

B. @Injectable() export class FeatureModule {}

C. @Module({ controllers: [], providers: [] }) export class FeatureModule {}

D. export class FeatureModule {}

Solution

1. Step 1: Recall the decorator for modules

   Feature modules use the @Module decorator with metadata like controllers and providers.

2. Step 2: Match options with correct decorator

   Only @Module({ controllers: [], providers: [] }) export class FeatureModule {} uses @Module with controllers and providers arrays, which is correct syntax.

3. Final Answer:

   @Module({ controllers: [], providers: [] }) export class FeatureModule {} -> Option C

4. Quick Check:

   @Module decorator defines modules = B [OK]

Hint: Use @Module decorator with controllers and providers [OK]

Common Mistakes:

• Using @Controller or @Injectable instead of @Module
• Forgetting to add the decorator
• Defining empty classes without decorators

3. Given this feature module code, what will be the output when the getHello() method is called from HelloController?

@Module({
  controllers: [HelloController],
  providers: [HelloService],
})
export class HelloModule {}

@Injectable()
export class HelloService {
  getHello() {
    return 'Hello from service!';
  }
}

@Controller()
export class HelloController {
  constructor(private readonly helloService: HelloService) {}

  @Get()
  getHello() {
    return this.helloService.getHello();
  }
}

medium

A. undefined

B. "Hello from controller!"

C. Runtime error due to missing provider

D. "Hello from service!"

Solution

1. Step 1: Understand dependency injection in the module

   The HelloService is provided in the module and injected into HelloController.

2. Step 2: Trace the method call

   The controller's getHello calls helloService.getHello(), which returns 'Hello from service!'.

3. Final Answer:

   "Hello from service!" -> Option D

4. Quick Check:

   Service method returns string = C [OK]

Hint: Controller calls service method returning string [OK]

Common Mistakes:

• Assuming controller returns its own string
• Thinking provider is missing causing error
• Confusing method names or return values

4. Identify the error in this feature module definition:

@Module({
  controllers: [UserController],
  providers: [UserService],
})
export class UserModule {}

@Injectable()
export class UserService {}

@Controller()
export class UserController {
  constructor(userService: UserService) {}
}

medium

A. Missing access modifier 'private' in constructor injection

B. UserService is not decorated with @Injectable()

C. UserController is missing @Controller() decorator

D. UserService is not listed in providers array

Solution

1. Step 1: Check constructor injection syntax

   In NestJS, injected dependencies must have an access modifier like private or public to create a class property.

2. Step 2: Identify the missing modifier

   The constructor parameter 'userService' lacks 'private' or 'public', so it won't be assigned automatically.

3. Final Answer:

   Missing access modifier 'private' in constructor injection -> Option A

4. Quick Check:

   Constructor injection needs access modifier = A [OK]

Hint: Constructor injection needs private/public keyword [OK]

Common Mistakes:

• Forgetting private/public in constructor parameters
• Assuming @Injectable is missing when it is present
• Confusing decorator placement

5. You want to create a feature module that imports another feature module to reuse its services. Which of the following is the correct way to import AuthModule into UserModule?

hard

A. @Module({ imports: [AuthModule], controllers: [UserController], providers: [UserService] }) export class UserModule {}

B. @Module({ controllers: [UserController], providers: [UserService] }) export class UserModule { constructor(private authModule: AuthModule) {} }

C. @Module({ exports: [AuthModule], controllers: [UserController], providers: [UserService] }) export class UserModule {}

D. @Module({ imports: [], controllers: [UserController], providers: [UserService] }) export class UserModule {}

Solution

1. Step 1: Understand module imports in NestJS

   To reuse services from another module, you must import that module in the imports array.

2. Step 2: Identify correct import usage

   @Module({ imports: [AuthModule], controllers: [UserController], providers: [UserService] }) export class UserModule {} correctly adds AuthModule to imports, allowing UserModule to use its exported providers.

3. Final Answer:

   @Module({ imports: [AuthModule], controllers: [UserController], providers: [UserService] }) export class UserModule {} -> Option A

4. Quick Check:

   Import modules via imports array = A [OK]

Hint: Use imports array to include other feature modules [OK]

Common Mistakes:

• Trying to inject modules via constructor instead of imports
• Using exports instead of imports to include modules
• Leaving imports array empty when reusing modules