Environment-based configuration in NestJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

How does NestJS load environment variables with ConfigModule?

Consider this NestJS module setup:

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

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

What happens when the app starts?

A NestJS requires manual import of ConfigService in every module to access variables.

B NestJS ignores .env files and only uses system environment variables.

C NestJS reads variables from a .env file and makes them available globally via ConfigService.

D NestJS throws an error if .env file is missing, stopping the app.

💡 Hint

Think about what isGlobal: true means in ConfigModule.

Setting isGlobal: true in ConfigModule.forRoot() loads environment variables from a .env file and makes the ConfigService available throughout the app without needing to import it in every module.

📝 Syntax

intermediate

Which code correctly accesses an environment variable in a NestJS service?

Given the ConfigService is injected, which code snippet correctly gets the DATABASE_URL variable?

NestJS

constructor(private configService: ConfigService) {}

getDbUrl() {
  // Which line is correct?
}

A return this.configService.getDatabaseUrl();

B return process.env.DATABASE_URL();

C return this.configService.env.DATABASE_URL;

D return this.configService.get('DATABASE_URL');

💡 Hint

Check the official method to get env variables from ConfigService.

The ConfigService provides a get() method to retrieve environment variables by name. Using process.env directly is possible but not recommended in NestJS.

🔧 Debug

advanced

Why does this NestJS app fail to load environment variables?

Look at this code snippet:

ConfigModule.forRoot({
  envFilePath: '.env.production',
  isGlobal: true,
});

The app does not load variables from .env.production. What is the likely cause?

A The <code>isGlobal</code> option disables loading environment files.

B The <code>envFilePath</code> path is relative to the process working directory, which may differ from the source file location.

C The <code>ConfigModule</code> must be imported in every module to load env files.

D NestJS only supports <code>.env</code> files and ignores custom filenames.

💡 Hint

Consider where the app runs and where the file is located.

The envFilePath is resolved relative to the current working directory when the app starts. If the file is not in that directory, the variables won't load. The other options are incorrect because isGlobal enables global access, and NestJS supports custom env file names.

❓ state_output

advanced

What is the value of config after this code runs?

Given this code:

ConfigModule.forRoot({
  load: [() => ({
    port: parseInt(process.env.PORT) || 3000,
    mode: process.env.MODE || 'dev',
  })],
  isGlobal: true,
});

// Assume process.env.PORT = '0', process.env.MODE is undefined

const config = configService.get('port');

What is the value of config?

A 0

B NaN

C 3000

D undefined

💡 Hint

Remember how parseInt and || work with 0.

parseInt('0') returns 0, which is falsy. Thus, parseInt(process.env.PORT) || 3000 evaluates to 3000. The loaded config sets port: 3000, so configService.get('port') returns 3000.

🧠 Conceptual

expert

Which statement about NestJS environment configuration is TRUE?

Choose the correct statement about environment-based configuration in NestJS.

A ConfigModule can load multiple environment files conditionally based on NODE_ENV using a custom function in envFilePath.

B ConfigModule requires manual injection in every service to access environment variables.

C Environment variables must be declared in a TypeScript interface to be accessible via ConfigService.

D ConfigService automatically reloads environment variables if the .env file changes during runtime.

💡 Hint

Think about how to load different env files for development and production.

ConfigModule's envFilePath option can accept a function that returns different file paths based on process.env.NODE_ENV, allowing conditional loading of environment files. The other options are false: ConfigService does not auto-reload env files, variables do not require TypeScript interfaces, and ConfigModule can be global to avoid manual injection everywhere.