Custom configuration files in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the ConfigModule with a custom configuration file.

NestJS

import { ConfigModule } from '@nestjs/config';

@Module({
  imports: [ConfigModule.forRoot({
    load: [[1]],
  })],
})
export class AppModule {}

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

AConfigModule

BConfigService

CconfigFile

DcustomConfig

Attempts:

3 left

💡 Hint

Common Mistakes

Passing ConfigService instead of the config function.

Using ConfigModule inside the load array.

Passing a string instead of a function or object.

You need to pass a function or object that returns your custom configuration. Here, customConfig is the correct import representing your config file.

2fill in blank

medium

Complete the code to create a custom configuration file exporting a function.

NestJS

export default function [1]() {
  return {
    port: parseInt(process.env.PORT, 10) || 3000,
  };
}

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

Aconfig

BConfigModule

CcustomConfig

DConfigService

Attempts:

3 left

💡 Hint

Common Mistakes

Using ConfigModule as function name.

Not exporting a default function.

Returning a non-object value.

The custom configuration file should export a default function, here named customConfig, that returns the configuration object.

3fill in blank

hard

Fix the error in the code to inject the ConfigService and get the custom port value.

NestJS

import { ConfigService } from '@nestjs/config';

@Injectable()
export class AppService {
  constructor(private readonly configService: [1]) {}

  getPort(): number {
    return this.configService.get<number>('port');
  }
}

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

AConfigModule

BConfigService

CcustomConfig

DConfig

Attempts:

3 left

💡 Hint

Common Mistakes

Injecting ConfigModule instead of ConfigService.

Using the config function name as type.

Forgetting to mark the constructor parameter as readonly.

You must inject ConfigService to access configuration values inside your service.

4fill in blank

hard

Fill both blanks to create a custom configuration file that reads a database URL and exports it.

NestJS

export default function [1]() {
  return {
    databaseUrl: process.env.[2] || 'mongodb://localhost:27017',
  };
}

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

AdatabaseConfig

BDATABASE_URL

CDB_URL

Dconfig

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase or camelCase for environment variable names.

Using generic function names like config.

Forgetting to export a default function.

The function name databaseConfig is descriptive for database settings. The environment variable DATABASE_URL is a common standard for database connection strings.

5fill in blank

hard

Fill all three blanks to use the custom configuration in a service and get the database URL.

NestJS

import { Injectable } from '@nestjs/common';
import { [1] } from '@nestjs/config';

@Injectable()
export class DatabaseService {
  constructor(private readonly [2]: [1]) {}

  getDatabaseUrl(): string {
    return this.[2].get<string>('databaseUrl');
  }
}

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

AConfigService

BconfigService

CdatabaseConfig

DConfigModule

Attempts:

3 left

💡 Hint

Common Mistakes

Using ConfigModule instead of ConfigService.

Naming the injected variable the same as the class.

Importing the custom config function instead of ConfigService.

You import and inject ConfigService to access configuration values. The injected variable is commonly named configService.

Practice

1. What is the main purpose of using custom configuration files in a NestJS application?

easy

A. To write all logic inside configuration files

B. To keep app settings organized and separate from the main code

C. To replace the main app module

D. To store user data permanently

Solution

1. Step 1: Understand configuration role

   Custom configuration files are used to keep settings like API keys or database info separate from the main code.

2. Step 2: Identify the correct purpose

   This separation helps organize the app and makes it easier to change settings without touching code logic.

3. Final Answer:

   To keep app settings organized and separate from the main code -> Option B

4. Quick Check:

   Custom config files organize settings [OK]

Hint: Custom configs separate settings from code for clarity [OK]

Common Mistakes:

• Thinking config files hold app logic
• Confusing config files with database storage
• Assuming config files replace main modules

2. Which syntax correctly creates a named custom configuration file using registerAs in NestJS?

easy

A. export const config = registerAs('app', () => ({ port: 3000 }));

B. registerAs('app', { port: 3000 });

C. export default registerAs('app', () => ({ port: 3000 }));

D. registerAs('app', () => port: 3000);

Solution

1. Step 1: Understand registerAs usage

   The registerAs function takes a name and a function returning a config object.

2. Step 2: Check syntax correctness

   export const config = registerAs('app', () => ({ port: 3000 })); correctly exports a constant assigned to registerAs with a function returning an object.

3. Final Answer:

   export const config = registerAs('app', () => ({ port: 3000 })); -> Option A

4. Quick Check:

   registerAs needs a name and a function returning an object [OK]

Hint: Use export const with registerAs and a function returning an object [OK]

Common Mistakes:

• Omitting export or const keywords
• Passing object directly instead of a function
• Incorrect arrow function syntax

3. Given this custom config file:

export const databaseConfig = registerAs('database', () => ({ host: 'localhost', port: 5432 }));

And this module setup:

ConfigModule.forRoot({ load: [databaseConfig] })

What will configService.get('database.host') return?

medium

A. Error: Config not found

B. 'database.host'

C. undefined

D. 'localhost'

Solution

1. Step 1: Understand config loading

   The databaseConfig is loaded into ConfigModule with load, making its keys accessible.

2. Step 2: Access nested config value

   Using configService.get('database.host') accesses the 'host' key inside the 'database' config, which is 'localhost'.

3. Final Answer:

   'localhost' -> Option D

4. Quick Check:

   Nested config keys return their values [OK]

Hint: Use dot notation to get nested config values [OK]

Common Mistakes:

• Expecting the whole object instead of a value
• Using wrong key names
• Not loading config before accessing

4. What is wrong with this custom config file code?

export const appConfig = registerAs('app', () => { port: 3000 });

medium

A. The config name 'app' is invalid

B. Missing import of registerAs

C. The arrow function does not return the object properly

D. The port value must be a string

Solution

1. Step 1: Check arrow function return

   The arrow function uses curly braces without a return statement, so it returns undefined instead of the object.

2. Step 2: Correct syntax for returning object

   To return an object directly, wrap it in parentheses: () => ({ port: 3000 }).

3. Final Answer:

   The arrow function does not return the object properly -> Option C

4. Quick Check:

   Arrow functions need parentheses to return objects directly [OK]

Hint: Wrap object in parentheses to return from arrow function [OK]

Common Mistakes:

• Using curly braces without return in arrow functions
• Assuming config name must be special
• Thinking port must be string

5. You want to create two custom config files, appConfig and dbConfig, and load both in your NestJS app. Which setup correctly loads and accesses the dbConfig.username value?

hard

A. Load both configs in ConfigModule.forRoot({ load: [appConfig, dbConfig] }) and get with configService.get('dbConfig.username')

B. Load only appConfig and get dbConfig.username directly

C. Load both configs but access dbConfig.username with configService.get('username')

D. Load configs separately in different modules without forRoot

Solution

1. Step 1: Load multiple configs together

   Use ConfigModule.forRoot({ load: [appConfig, dbConfig] }) to load both custom configs at app start.

2. Step 2: Access nested config by namespace

   Access dbConfig.username using configService.get('dbConfig.username') because configs are namespaced by their registration name.

3. Final Answer:

   Load both configs in ConfigModule.forRoot({ load: [appConfig, dbConfig] }) and get with configService.get('dbConfig.username') -> Option A

4. Quick Check:

   Load all configs and use namespaced keys to access [OK]

Hint: Load all configs in forRoot and use dot keys to access [OK]

Common Mistakes:

• Loading only one config but accessing another
• Accessing keys without namespace prefix
• Trying to load configs outside forRoot