Dynamic modules in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a dynamic module with a static method.

NestJS

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

@Module({})
export class ConfigModule {
  static forRoot(): [1] {
    return {
      module: ConfigModule,
    };
  }
}

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

ADynamicModule

BModule

CProvider

DInjectable

Attempts:

3 left

💡 Hint

Common Mistakes

Returning a plain Module instead of DynamicModule

Forgetting to return an object from the static method

The static method forRoot() must return a DynamicModule to configure the module dynamically.

2fill in blank

medium

Complete the code to inject a configuration value into the dynamic module.

NestJS

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

@Module({})
export class ConfigModule {
  static forRoot(configValue: string): DynamicModule {
    return {
      module: ConfigModule,
      providers: [
        {
          provide: 'CONFIG_VALUE',
          useValue: [1],
        },
      ],
      exports: ['CONFIG_VALUE'],
    };
  }
}

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

A'configValue'

BConfigModule

CconfigValue

DCONFIG_VALUE

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string literal instead of the variable

Using the module name instead of the config value

The useValue should be the parameter configValue passed to the static method.

3fill in blank

hard

Fix the error in the dynamic module import syntax.

NestJS

import { Module, DynamicModule } from '@nestjs/common';
import { ConfigModule } from './config.module';

@Module({
  imports: [ConfigModule.[1]({ apiKey: '123' })],
})
export class AppModule {}

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

Aregister

BforRoot

CuseFactory

Dcreate

Attempts:

3 left

💡 Hint

Common Mistakes

Using register or create which are not standard method names here

Using useFactory which is for providers, not module imports

The dynamic module method to import is usually named forRoot to configure the module.

4fill in blank

hard

Fill both blanks to create a dynamic module that imports another module and provides a service.

NestJS

import { Module, DynamicModule } from '@nestjs/common';
import { HttpModule } from '@nestjs/axios';

@Module({})
export class ApiModule {
  static forRoot(apiUrl: string): DynamicModule {
    return {
      module: ApiModule,
      imports: [[1]],
      providers: [
        {
          provide: 'API_URL',
          useValue: [2],
        },
      ],
      exports: ['API_URL'],
    };
  }
}

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

AHttpModule

BapiUrl

CConfigModule

D'apiUrl'

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string literal instead of the variable for useValue

Importing the wrong module

The imports array should include HttpModule, and the useValue should be the apiUrl parameter.

5fill in blank

hard

Fill all three blanks to create a dynamic module that registers a provider with a factory and injects a token.

NestJS

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

@Module({})
export class LoggerModule {
  static forRoot(level: string): DynamicModule {
    return {
      module: LoggerModule,
      providers: [
        {
          provide: 'LOG_LEVEL',
          useValue: [1],
        },
        {
          provide: 'LOGGER_SERVICE',
          useFactory: (logLevel: string) => new LoggerService(logLevel),
          inject: [[2]],
        },
      ],
      exports: [[3]],
    };
  }
}

class LoggerService {
  constructor(private level: string) {}
}

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

Alevel

B'LOG_LEVEL'

C'LOGGER_SERVICE'

Attempts:

3 left

💡 Hint

Common Mistakes

Injecting the service token instead of the log level token

Exporting the log level token instead of the service token

useValue should be the level parameter; inject array should contain 'LOG_LEVEL'; exports should include 'LOGGER_SERVICE'.

Practice

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

easy

A. To automatically generate database schemas

B. To create modules without any providers or exports

C. To replace the need for controllers in an application

D. To allow configuration of modules with custom options at runtime

Solution

1. Step 1: Understand dynamic module concept

   Dynamic modules let you pass custom options to configure the module when importing it.

2. Step 2: Identify the main purpose

   This flexibility helps reuse modules with different settings instead of hardcoding them.

3. Final Answer:

   To allow configuration of modules with custom options at runtime -> Option D

4. Quick Check:

   Dynamic modules = configurable modules [OK]

Hint: Dynamic modules customize modules with options [OK]

Common Mistakes:

• Thinking dynamic modules remove controllers
• Believing dynamic modules auto-generate schemas
• Assuming dynamic modules have no providers

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

easy

A. constructor(options: ModuleOptions): void { ... }

B. static forRoot(options: ModuleOptions): DynamicModule { ... }

C. export function createModule(options: ModuleOptions) { ... }

D. async initialize(options: ModuleOptions): Promise<void> { ... }

Solution

1. Step 1: Recall dynamic module pattern

   Dynamic modules use a static method, commonly named forRoot, returning a DynamicModule object.

2. Step 2: Match method signature

   Only a static method can be called without creating an instance, fitting the dynamic module pattern.

3. Final Answer:

   static forRoot(options: ModuleOptions): DynamicModule { ... } -> Option B

4. Quick Check:

   Dynamic module method = static forRoot [OK]

Hint: Dynamic modules use static forRoot method [OK]

Common Mistakes:

• Using constructor instead of static method
• Defining dynamic module as a normal function
• Making dynamic module method async without returning DynamicModule

3. Given this dynamic module code, what will be the value of the exported provider's token?

export class LoggerModule {
  static forRoot(prefix: string): DynamicModule {
    return {
      module: LoggerModule,
      providers: [
        { provide: 'LOGGER_PREFIX', useValue: prefix },
      ],
      exports: ['LOGGER_PREFIX'],
    };
  }
}

medium

A. 'prefix'

B. 'LoggerModule'

C. 'LOGGER_PREFIX'

D. 'useValue'

Solution

1. Step 1: Identify provider token

   The provider uses the key 'provide' with value 'LOGGER_PREFIX' which is the token for injection.

2. Step 2: Confirm exported token

   The exports array includes 'LOGGER_PREFIX', so this token is available outside the module.

3. Final Answer:

   'LOGGER_PREFIX' -> Option C

4. Quick Check:

   Provider token = 'LOGGER_PREFIX' [OK]

Hint: Provider token is the 'provide' string value [OK]

Common Mistakes:

• Confusing module name with provider token
• Using variable name 'prefix' as token
• Thinking useValue is the token

4. Identify the error in this dynamic module definition:

export class CacheModule {
  static forRoot(options: { ttl: number }): DynamicModule {
    return {
      module: CacheModule,
      providers: [
        { provide: 'CACHE_TTL', useFactory: (options) => options.ttl },
      ],
      exports: ['CACHE_TTL'],
    };
  }
}

medium

A. The useFactory function cannot access options parameter directly

B. The module property should be a string, not a class

C. Exports array must include providers, not strings

D. Static methods cannot return DynamicModule

Solution

1. Step 1: Analyze useFactory context

   The useFactory function runs later and cannot directly access the outer options variable without injection.

2. Step 2: Identify correct pattern

   To use options inside useFactory, it must be passed via inject or closure properly; direct access causes runtime error.

3. Final Answer:

   The useFactory function cannot access options parameter directly -> Option A

4. Quick Check:

   useFactory needs inject or closure for options [OK]

Hint: useFactory can't directly use outer variables [OK]

Common Mistakes:

• Thinking module property must be string
• Believing exports must list provider objects
• Assuming static methods can't return DynamicModule

5. You want to create a dynamic module that accepts a configuration object and provides two services using that config. Which approach correctly implements this pattern?

hard

A. Use a static forRoot method returning a DynamicModule with providers using useValue for config and export both services

B. Create a constructor in the module class that sets config and exports services directly

C. Define services inside the module without any configuration and import them normally

D. Use a global module without any providers and configure services externally

Solution

1. Step 1: Understand dynamic module pattern for config

   Dynamic modules use a static method (like forRoot) to accept config and return a DynamicModule object with providers.

2. Step 2: Provide config and services properly

   Use useValue or useFactory to inject config into providers, and export services to make them available outside.

3. Final Answer:

   Use a static forRoot method returning a DynamicModule with providers using useValue for config and export both services -> Option A

4. Quick Check:

   Dynamic module with static forRoot and providers = Use a static forRoot method returning a DynamicModule with providers using useValue for config and export both services [OK]

Hint: Use static forRoot with providers and exports [OK]

Common Mistakes:

• Trying to configure modules via constructor
• Not exporting services after providing them
• Using global module without providers for config