Environment-based configuration in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the ConfigModule in a NestJS module.

NestJS

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

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

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

AforRoot

Bregister

Cinitialize

Dsetup

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name that does not exist on ConfigModule.

Forgetting to call the method as a function.

The ConfigModule.forRoot() method loads environment variables and makes them available throughout the app.

2fill in blank

medium

Complete the code to inject ConfigService into a service constructor.

NestJS

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

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

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

Aconfig

BconfigSrv

CserviceConfig

DconfigService

Attempts:

3 left

💡 Hint

Common Mistakes

Using a generic or unclear variable name.

Not matching the injected type with the variable name.

The common convention is to name the injected ConfigService instance configService for clarity.

3fill in blank

hard

Fix the error in accessing an environment variable using ConfigService.

NestJS

const port = this.configService.[1]('PORT');

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

AgetValue

Bget

Cfetch

Dretrieve

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent methods like getValue or fetch.

Trying to access environment variables directly without ConfigService.

The correct method to get environment variables from ConfigService is get.

4fill in blank

hard

Fill in the blank to access an environment variable with a default value fallback.

NestJS

const dbHost = this.configService.[1]('DATABASE_HOST', 'localhost');

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

Aget

Bdefault

Cundefined

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect method names.

Trying to use keywords like undefined or null as default values incorrectly.

The get method accepts a second argument as a default value if the environment variable is not set.

5fill in blank

hard

Fill all three blanks to define a custom configuration loader function.

NestJS

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

export const customConfig = registerAs([2], () => ({
  port: parseInt(process.env.[3] || '3000', 10),
}));

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

AregisterAs

Bconfig

CPORT

DConfigModule

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing import names.

Using wrong environment variable names.

Not wrapping the config in a function.

registerAs is used to create a named configuration. The function returns an object with the port read from environment variable PORT.

Practice

1. What is the main purpose of using environment-based configuration in a NestJS application?

easy

A. To write more complex code logic

B. To hardcode all secrets inside the source files

C. To increase the size of the application

D. To change app settings without modifying the code

Solution

1. Step 1: Understand environment-based configuration

   It allows changing settings like database URLs or API keys without changing the app code.

2. Step 2: Identify the correct purpose

   Changing settings without code changes helps adapt the app to different environments easily.

3. Final Answer:

   To change app settings without modifying the code -> Option D

4. Quick Check:

   Environment config = change settings without code [OK]

Hint: Think: config changes without touching code [OK]

Common Mistakes:

• Confusing config with code logic
• Assuming config increases app size
• Hardcoding secrets inside source files

2. Which NestJS module is used to load environment variables for configuration?

easy

A. ConfigModule

B. DatabaseModule

C. HttpModule

D. LoggerModule

Solution

1. Step 1: Recall NestJS modules for config

   The ConfigModule is designed to load and manage environment variables.

2. Step 2: Match module to purpose

   HttpModule handles HTTP, DatabaseModule handles DB, LoggerModule handles logs, so ConfigModule is correct.

3. Final Answer:

   ConfigModule -> Option A

4. Quick Check:

   ConfigModule loads env variables [OK]

Hint: ConfigModule = environment variables loader [OK]

Common Mistakes:

• Choosing unrelated modules like HttpModule
• Confusing ConfigModule with DatabaseModule
• Assuming LoggerModule manages config

3. Given this code snippet in a NestJS service:

constructor(private configService: ConfigService) {}

getDbHost() {
  return this.configService.get('DATABASE_HOST');
}

What will getDbHost() return if the environment variable DATABASE_HOST is set to localhost?

medium

A. DATABASE_HOST

B. undefined

C. localhost

D. null

Solution

1. Step 1: Understand ConfigService.get()

   This method returns the value of the environment variable key passed, here 'DATABASE_HOST'.

2. Step 2: Check environment variable value

   The variable DATABASE_HOST is set to 'localhost', so get() returns 'localhost'.

3. Final Answer:

   localhost -> Option C

4. Quick Check:

   ConfigService.get('DATABASE_HOST') = 'localhost' [OK]

Hint: ConfigService.get returns env var value [OK]

Common Mistakes:

• Expecting the key name instead of its value
• Assuming undefined if variable exists
• Confusing null with undefined

4. You wrote this code to load environment variables in NestJS:

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

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

But your app crashes with an error saying environment variables are undefined. What is the likely cause?

medium

A. You must call ConfigService.get() inside main.ts only

B. You forgot to create a .env file or set environment variables

C. You need to import HttpModule as well

D. ConfigModule.forRoot() should be called inside a service, not module

Solution

1. Step 1: Check environment variable source

   ConfigModule loads variables from .env file or system environment. If missing, variables are undefined.

2. Step 2: Identify common mistake

   Not having a .env file or not setting variables causes undefined values and app crash.

3. Final Answer:

   You forgot to create a .env file or set environment variables -> Option B

4. Quick Check:

   Missing .env file = undefined env vars [OK]

Hint: Always create .env file or set env vars [OK]

Common Mistakes:

• Thinking ConfigModule.forRoot() is misplaced
• Assuming HttpModule is needed for config
• Calling ConfigService.get() only in main.ts

5. You want to load different database URLs for development and production in NestJS using environment variables. Which approach correctly uses ConfigModule to load .env.development or .env.production based on NODE_ENV?

hard

A. ConfigModule.forRoot({ envFilePath: `.env.${process.env.NODE_ENV}` })

B. ConfigModule.forRoot({ envFilePath: '.env' })

C. ConfigModule.forRoot({ envFilePath: '.env.production' }) always

D. ConfigModule.forRoot({ envFilePath: '.env.development' }) always

Solution

1. Step 1: Understand dynamic env file loading

   Using envFilePath with template string allows loading .env files based on NODE_ENV value.

2. Step 2: Check options

   ConfigModule.forRoot({ envFilePath: `.env.${process.env.NODE_ENV}` }) dynamically loads .env.development or .env.production depending on NODE_ENV, others load fixed files.

3. Final Answer:

   ConfigModule.forRoot({ envFilePath: `.env.${process.env.NODE_ENV}` }) -> Option A

4. Quick Check:

   Dynamic envFilePath = correct multi-env config [OK]

Hint: Use template string with NODE_ENV for envFilePath [OK]

Common Mistakes:

• Hardcoding envFilePath to one file always
• Not using process.env.NODE_ENV in path
• Assuming default .env handles all environments