Module decorator and metadata in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a NestJS module with the @Module decorator.

NestJS

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

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

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

Aimports

Bcomponents

Cservices

Dcontrollers

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'components' or 'services' which are not valid properties in @Module.

Confusing 'controllers' with 'imports'.

The @Module decorator uses the imports property to specify modules to import.

2fill in blank

medium

Complete the code to add a controller to the module metadata.

NestJS

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

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

AUserEntity

BUserService

CAppModule

DUserController

Attempts:

3 left

💡 Hint

Common Mistakes

Putting services or entities inside the controllers array.

Confusing controller with service names.

The controllers array should list controller classes like UserController.

3fill in blank

hard

Fix the error in the module metadata by completing the providers array correctly.

NestJS

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

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

AAuthModule

BAuthController

CAuthService

DAuthEntity

Attempts:

3 left

💡 Hint

Common Mistakes

Adding controllers or modules to providers array.

Confusing entities with providers.

The providers array should include service classes like AuthService that provide functionality.

4fill in blank

hard

Fill both blanks to complete the module metadata with imports and exports.

NestJS

@Module({
  [1]: [CommonModule],
  [2]: [CommonModule],
})
export class SharedModule {}

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

Aimports

Bproviders

Cexports

Dcontrollers

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up exports with providers or controllers.

Using providers instead of exports to share modules.

The imports array brings in modules, and exports makes them available to other modules.

5fill in blank

hard

Fill all three blanks to complete a module with imports, controllers, and providers.

NestJS

@Module({
  [1]: [DatabaseModule],
  [2]: [AppController],
  [3]: [AppService],
})
export class AppModule {}

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

Aimports

Bcontrollers

Cproviders

Dexports

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping controllers and providers.

Putting modules in providers or controllers.

The imports array includes other modules, controllers lists controllers, and providers lists services.

Practice

1. What is the main purpose of the @Module decorator in NestJS?

easy

A. To define the database connection settings

B. To group related components like controllers and providers together

C. To create HTTP routes directly

D. To style the application UI

Solution

1. Step 1: Understand the role of @Module

   The @Module decorator organizes related parts of the app such as controllers and providers.

2. Step 2: Compare options

   The options describing database connections, HTTP routing, or UI styling are unrelated to the main role of @Module.

3. Final Answer:

   To group related components like controllers and providers together -> Option B

4. Quick Check:

   @Module groups controllers & providers [OK]

Hint: Remember: @Module bundles controllers and providers [OK]

Common Mistakes:

• Thinking @Module sets up database connections
• Confusing @Module with routing decorators
• Assuming @Module styles the UI

2. Which of the following is the correct way to define a NestJS module with a controller named AppController and a provider named AppService?

easy

A. @Module({ controller: [AppController], provider: [AppService] })

B. @Module({ controllers: AppController, providers: AppService })

C. @Module({ controllers: (AppController), providers: (AppService) })

D. @Module({ controllers: [AppController], providers: [AppService] })

Solution

1. Step 1: Check correct property names and syntax

   The @Module decorator expects arrays for controllers and providers properties.

2. Step 2: Validate each option

   Singular property names like 'controller'/'provider', missing array brackets, or parentheses instead of square brackets are incorrect. The correct syntax uses plural 'controllers'/'providers' with arrays.

3. Final Answer:

   @Module({ controllers: [AppController], providers: [AppService] }) -> Option D

4. Quick Check:

   controllers & providers must be arrays [OK]

Hint: Use arrays for controllers and providers in @Module [OK]

Common Mistakes:

• Using singular property names like controller or provider
• Not wrapping controllers/providers in arrays
• Using parentheses instead of square brackets

3. Given the following module definition, what will be the value of AppModule.imports.length?

@Module({
  imports: [CommonModule, DatabaseModule],
  controllers: [AppController],
  providers: [AppService]
})
export class AppModule {}

medium

A. 2

B. 1

C. 0

D. Undefined

Solution

1. Step 1: Identify the imports array length

   The imports array contains two modules: CommonModule and DatabaseModule.

2. Step 2: Calculate the length property

   Since there are two items, AppModule.imports.length equals 2.

3. Final Answer:

   2 -> Option A

4. Quick Check:

   imports array length = 2 [OK]

Hint: Count modules inside imports array for length [OK]

Common Mistakes:

• Assuming imports is empty or undefined
• Confusing imports with controllers or providers
• Forgetting to count all items in the array

4. Identify the error in this NestJS module definition:

@Module({
  imports: CommonModule,
  controllers: [AppController],
  providers: [AppService]
})
export class AppModule {}

medium

A. imports should be an array, not a single module

B. controllers should not be inside an array

C. providers property is missing

D. Module class must have a constructor

Solution

1. Step 1: Check the imports property type

   The imports property must be an array, but here it is a single module without brackets.

2. Step 2: Verify other properties

   controllers and providers are correctly arrays. The module class does not require a constructor by default.

3. Final Answer:

   imports should be an array, not a single module -> Option A

4. Quick Check:

   imports must be array [OK]

Hint: Always wrap imports in square brackets [OK]

Common Mistakes:

• Using single module without array in imports
• Thinking controllers can't be arrays
• Assuming constructor is mandatory

5. You want to share a service SharedService from SharedModule so other modules can use it. Which is the correct way to configure SharedModule to allow this?

hard

A. @Module({ imports: [SharedService], exports: [SharedService] })

B. @Module({ providers: [SharedService] })

C. @Module({ providers: [SharedService], exports: [SharedService] })

D. @Module({ exports: [SharedService] })

Solution

1. Step 1: Understand sharing services via exports

   To share a service, it must be both provided and exported in the module metadata.

2. Step 2: Analyze options

   Sharing requires listing the service in both providers (to provide it) and exports (to make it available to importers). imports is for modules, not services. Missing either providers or exports prevents sharing.

3. Final Answer:

   @Module({ providers: [SharedService], exports: [SharedService] }) -> Option C

4. Quick Check:

   providers AND exports needed [OK]

Hint: Provide and export service to share it with other modules [OK]

Common Mistakes:

• Forgetting to export the service
• Trying to import a service instead of providing it
• Only exporting without providing the service