Environment variables in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to load environment variables in a NestJS service.

NestJS

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

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

  getDatabaseHost(): string {
    return this.configService.get<string>('DATABASE_HOST');
  }
}

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

AconfigSrv

BConfigService

Cconfig

DconfigService

Attempts:

3 left

💡 Hint

Common Mistakes

Using the class name instead of the instance name in the constructor.

Using a name that does not match the injected service.

The constructor parameter should be named configService to use the injected ConfigService instance.

2fill in blank

medium

Complete the code to access an environment variable named 'PORT' as a number.

NestJS

const port = this.configService.get<number>([1]);

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

A'port'

B'PORT'

C'Port'

D'server_port'

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase or mixed case keys that do not match the environment variable.

Using a wrong variable name.

Environment variables are case-sensitive and usually uppercase. The correct key is 'PORT'.

3fill in blank

hard

Fix the error in the code to correctly load environment variables in the main app module.

NestJS

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

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

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

Aload

Bregister

CforRoot

Dinit

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent method like 'load' or 'init'.

Forgetting to call the method as a function.

The ConfigModule must be imported with forRoot() to load environment variables globally.

4fill in blank

hard

Fill both blanks to create a configuration object that reads 'API_KEY' and 'API_SECRET' from environment variables.

NestJS

export default () => ({
  apiKey: process.env.[1],
  apiSecret: process.env.[2],
});

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

AAPI_KEY

Bapi_key

CAPI_SECRET

Dapi_secret

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase or camelCase keys that do not match environment variables.

Mixing up the keys for apiKey and apiSecret.

Environment variables are usually uppercase and underscore separated. Use API_KEY and API_SECRET.

5fill in blank

hard

Fill all three blanks to create a NestJS service method that returns the port number from environment variables with a default fallback.

NestJS

getPort(): number {
  return this.configService.get<number>([1], [2]) ?? [3];
}

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

A'PORT'

Bundefined

C3000

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Passing wrong keys or default values.

Not providing a fallback value.

The method gets the 'PORT' variable, passes undefined as default value to get, and uses 3000 as fallback if undefined.

Practice

1. What is the main purpose of using environment variables in a NestJS application?

easy

A. To hardcode sensitive data like passwords in the source code

B. To write all configuration directly inside the main application file

C. To make the application run faster by avoiding configuration files

D. To keep configuration settings outside the code for security and flexibility

Solution

1. Step 1: Understand environment variables purpose

   Environment variables store settings like API keys or database URLs outside the code to keep them safe and easy to change.

2. Step 2: Compare options

   Only To keep configuration settings outside the code for security and flexibility correctly describes this purpose. Options A and B suggest unsafe practices, and D is incorrect about performance.

3. Final Answer:

   To keep configuration settings outside the code for security and flexibility -> Option D

4. Quick Check:

   Environment variables = external safe config [OK]

Hint: Environment variables keep secrets out of code [OK]

Common Mistakes:

• Hardcoding sensitive data inside source code
• Confusing environment variables with regular variables
• Thinking environment variables improve speed

2. Which of the following is the correct way to load environment variables in a NestJS app?

easy

A. Manually read .env file using fs module in every service

B. Use process.env directly without any module

C. Import ConfigModule with ConfigModule.forRoot() in the root module

D. Declare environment variables inside main.ts without ConfigModule

Solution

1. Step 1: Identify NestJS recommended method

   NestJS uses ConfigModule.forRoot() to load .env files and provide ConfigService.

2. Step 2: Evaluate other options

   Options A and C are possible but not recommended patterns. Declare environment variables inside main.ts without ConfigModule is incorrect because environment variables are external.

3. Final Answer:

   Import ConfigModule with ConfigModule.forRoot() in the root module -> Option C

4. Quick Check:

   ConfigModule.forRoot() loads env [OK]

Hint: Use ConfigModule.forRoot() to load .env [OK]

Common Mistakes:

• Reading .env manually everywhere
• Ignoring ConfigModule and using process.env directly
• Declaring env variables inside code files

3. Given this code snippet in a NestJS service:

constructor(private configService: ConfigService) {}

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

If the .env file contains DATABASE_HOST=localhost, what will getDbHost() return?

medium

A. undefined

B. localhost

C. DATABASE_HOST

D. null

Solution

1. Step 1: Understand ConfigService.get() behavior

   ConfigService.get('DATABASE_HOST') reads the value of DATABASE_HOST from loaded environment variables.

2. Step 2: Match with .env content

   The .env file sets DATABASE_HOST=localhost, so the method returns 'localhost'.

3. Final Answer:

   localhost -> Option B

4. Quick Check:

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

Hint: ConfigService.get returns env value by key [OK]

Common Mistakes:

• Expecting the key name instead of value
• Assuming undefined if ConfigModule not imported
• Confusing null with undefined

4. What is wrong with this NestJS module setup for environment variables?

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

medium

A. ConfigModule is imported without calling forRoot(), so env variables won't load

B. ConfigModule should be imported in providers, not imports

C. ConfigModule requires a .json config file, not .env

D. ConfigModule must be imported twice to work

Solution

1. Step 1: Check ConfigModule import syntax

   ConfigModule must be imported with forRoot() to load environment variables from .env file.

2. Step 2: Identify error in code

   The code imports ConfigModule directly without forRoot(), so env variables won't be loaded.

3. Final Answer:

   ConfigModule is imported without calling forRoot(), so env variables won't load -> Option A

4. Quick Check:

   ConfigModule.forRoot() needed to load env [OK]

Hint: Always use ConfigModule.forRoot() to load env [OK]

Common Mistakes:

• Importing ConfigModule without forRoot()
• Placing ConfigModule in providers instead of imports
• Thinking ConfigModule needs JSON config

5. You want to provide a default value for an environment variable PORT in NestJS if it is not set in the .env file. Which code snippet correctly achieves this in a service?

hard

A. const port = this.configService.get('PORT') || 3000;

B. const port = process.env.PORT ? 3000 : this.configService.get('PORT');

C. const port = this.configService.get('PORT', 3000);

D. const port = this.configService.get('PORT') && 3000;

Solution

1. Step 1: Understand default value logic

   If PORT is undefined or empty, use 3000 as default. Logical OR (||) works for this.

2. Step 2: Analyze options

   const port = this.configService.get('PORT') || 3000; uses || to provide default 3000 if get('PORT') is falsy. const port = process.env.PORT ? 3000 : this.configService.get('PORT'); reverses logic incorrectly. const port = this.configService.get('PORT', 3000); is invalid because get() does not take default param. const port = this.configService.get('PORT') && 3000; uses && which returns 3000 only if PORT is truthy, wrong logic.

3. Final Answer:

   const port = this.configService.get('PORT') || 3000; -> Option A

4. Quick Check:

   Use || to set default value [OK]

Hint: Use || to set default if env variable missing [OK]

Common Mistakes:

• Using && instead of || for default
• Passing default value as second argument to get()
• Reversing condition logic