Global modules in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to make the module global using the decorator.

NestJS

import { Module, [1] } from '@nestjs/common';

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

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

AGlobal

BInjectable

CController

DService

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Injectable instead of @Global

Forgetting to add the decorator

Confusing @Controller with @Global

The @Global() decorator marks a module as global, so it doesn't need to be imported everywhere.

2fill in blank

medium

Complete the code to export the service from the global module.

NestJS

import { Module, Global } from '@nestjs/common';
import { MyService } from './my.service';

@Global()
@Module({
  providers: [MyService],
  [1]: [MyService],
})
export class MyGlobalModule {}

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

Acomponents

Bimports

Ccontrollers

Dexports

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'imports' instead of 'exports'

Leaving out the exports array

Adding the service to controllers

The exports array makes the service available throughout the application since the module is global.

3fill in blank

hard

Fix the error in the code to properly use the global module.

NestJS

import { Module, Global } from '@nestjs/common';
import { ConfigService } from './config.service';

@Global()
@Module({
  providers: [ConfigService],
  exports: [[1]],
})
export class ConfigModule {}

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

AConfigController

BConfigModule

CConfigService

DConfigProvider

Attempts:

3 left

💡 Hint

Common Mistakes

Exporting the module class instead of the provider

Using a controller name in exports

Leaving exports empty

The exports array must list the provider to share it. Here, ConfigService is the provider to export.

4fill in blank

hard

Fill both blanks to create a global module that exports a service and imports another module.

NestJS

import { Module, [1] } from '@nestjs/common';
import { SharedModule } from './shared.module';
import { LoggerService } from './logger.service';

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

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

AGlobal

BInjectable

CSharedModule

DLoggerService

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Injectable instead of @Global

Importing the service instead of the module

Forgetting to export the service

The @Global() decorator marks the module global, and SharedModule is imported to use its exports.

5fill in blank

hard

Fill all three blanks to define a global module that imports another module, provides a service, and exports it.

NestJS

import { Module, [1] } from '@nestjs/common';
import { DatabaseModule } from './database.module';
import { AuthService } from './auth.service';

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

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

AGlobal

BDatabaseModule

CAuthService

DConfigModule

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up service and module names

Not exporting the provided service

Using wrong decorator names

The @Global() decorator makes the module global, DatabaseModule is imported, and AuthService is provided and exported.

Practice

1. What is the main purpose of marking a module with @Global() in NestJS?

easy

A. To disable dependency injection for the module

B. To make its providers available across the entire application without importing the module repeatedly

C. To automatically register the module as a controller

D. To restrict the module's providers to only one feature module

Solution

1. Step 1: Understand the role of @Global()

   The @Global() decorator marks a module so its providers can be used app-wide without importing it in every module.

2. Step 2: Compare options with this behavior

   Only To make its providers available across the entire application without importing the module repeatedly correctly describes this behavior; others describe unrelated or incorrect effects.

3. Final Answer:

   To make its providers available across the entire application without importing the module repeatedly -> Option B

4. Quick Check:

   Global modules share providers app-wide [OK]

Hint: Global modules share providers app-wide without imports [OK]

Common Mistakes:

• Thinking @Global restricts providers to one module
• Confusing @Global with controller registration
• Assuming @Global disables dependency injection

2. Which of the following is the correct way to declare a global module in NestJS?

easy

A. @Global() @Module({ providers: [MyService], exports: [MyService] }) export class MyModule {}

B. @Module({ global: true, providers: [MyService], exports: [MyService] }) export class MyModule {}

C. @GlobalModule() @Module({ providers: [MyService] }) export class MyModule {}

D. @Module({ providers: [MyService], global: true }) export class MyModule {}

Solution

1. Step 1: Recall the correct decorator for global modules

   In NestJS, @Global() is used above the module class to mark it global.

2. Step 2: Check syntax correctness

   @Global() @Module({ providers: [MyService], exports: [MyService] }) export class MyModule {} correctly uses @Global() and @Module() with providers and exports arrays.

3. Final Answer:

   @Global() @Module({ providers: [MyService], exports: [MyService] }) export class MyModule {} -> Option A

4. Quick Check:

   Use @Global() decorator above @Module() [OK]

Hint: Use @Global() decorator above @Module() to declare global module [OK]

Common Mistakes:

• Using 'global: true' inside @Module() which is invalid
• Using non-existent @GlobalModule() decorator
• Forgetting to export providers in global module

3. Given this global module declaration:

@Global()
@Module({
  providers: [ConfigService],
  exports: [ConfigService],
})
export class ConfigModule {}

What happens if another module imports ConfigModule again?

medium

A. The application will throw a runtime error due to duplicate imports

B. The providers from ConfigModule are duplicated and cause errors

C. The providers are shared globally, so importing again has no effect

D. The ConfigModule providers become private to the importing module

Solution

1. Step 1: Understand global module behavior on imports

   Global modules share their providers app-wide, so importing them multiple times does not duplicate providers.

2. Step 2: Analyze the effect of importing a global module again

   Importing a global module again is harmless; providers remain shared and singleton.

3. Final Answer:

   The providers are shared globally, so importing again has no effect -> Option C

4. Quick Check:

   Global modules share providers; repeated imports don't duplicate [OK]

Hint: Global modules share providers; repeated imports don't duplicate [OK]

Common Mistakes:

• Assuming repeated imports cause errors
• Thinking providers become private on re-import
• Confusing global modules with normal modules

4. Consider this code snippet:

@Global()
@Module({
  providers: [LoggerService],
  exports: [LoggerService],
})
export class LoggerModule {}

But when you try to inject LoggerService in another module, you get an error: Nest can't resolve dependencies. What is the likely cause?

medium

A. You forgot to import LoggerModule in the root module

B. You did not mark LoggerModule with @Global()

C. You forgot to export LoggerService from LoggerModule

D. You did not add @Injectable() to LoggerService

Solution

1. Step 1: Check the module declaration

   The module is marked global and exports LoggerService, so imports and exports are correct.

2. Step 2: Verify LoggerService setup

   If LoggerService lacks @Injectable(), NestJS cannot inject it, causing the error.

3. Final Answer:

   You did not add @Injectable() to LoggerService -> Option D

4. Quick Check:

   Missing @Injectable() on service causes injection errors [OK]

Hint: Check if service has @Injectable() decorator [OK]

Common Mistakes:

• Assuming global modules don't need imports anywhere
• Forgetting to export providers
• Confusing missing @Global() with injection errors

5. You want to create a global module that provides a configuration service with environment variables. Which of the following is the best practice to ensure the service is singleton and accessible everywhere without repeated imports?

hard

A. Mark the module with @Global(), export the service, and import it only once in the root module

B. Mark the module with @Global(), export the service, and import the module in every feature module

C. Mark the module with @Global(), export the service, and do not import it anywhere else

D. Do not mark the module global; import it in every module that needs it

Solution

1. Step 1: Understand global module usage

   Global modules provide their exported providers app-wide without needing to import them repeatedly.

2. Step 2: Determine import requirements for global modules

   Global modules must be imported once, typically in the root module; after that, providers are available app-wide without further imports.

3. Final Answer:

   Mark the module with @Global(), export the service, and import it only once in the root module -> Option A

4. Quick Check:

   Import global modules once in root module [OK]

Hint: Global modules: mark @Global(), export, import once in root [OK]

Common Mistakes:

• Importing global modules in every feature module
• Not importing global modules at all
• Not marking the module as global