Environment variables in NestJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

How does NestJS load environment variables?

Consider a NestJS application using the ConfigModule. What is the behavior when you import ConfigModule.forRoot() without any options?

NestJS

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

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

A It requires you to specify the path to the .env file explicitly or it won't load any variables.

B It only loads environment variables from process.env and ignores any .env files.

C It loads environment variables from a .env file in the project root by default.

D It throws an error if no .env file is found in the project root.

💡 Hint

Think about the default behavior of ConfigModule.forRoot() in NestJS.

By default, ConfigModule.forRoot() loads environment variables from a .env file located in the project root directory. You don't need to specify the path unless you want to load a different file.

❓ state_output

intermediate

What value does ConfigService return?

Given the following .env file and NestJS service code, what will be the output of the console.log?

NestJS

.env file content:
PORT=3000

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

@Injectable()
export class AppService {
  constructor(private configService: ConfigService) {}

  printPort() {
    console.log(this.configService.get('PORT'));
  }
}

A 3000

B undefined

C null

D Throws an error because PORT is a number but get returns string

💡 Hint

Remember how ConfigService reads values from .env files.

The ConfigService.get() method returns the value as a string from the environment variables loaded. Since PORT=3000 is set, it returns the string "3000".

📝 Syntax

advanced

Which option correctly loads a custom .env file path?

You want to load environment variables from a file named '.env.production' instead of the default '.env'. Which ConfigModule import is correct?

A ConfigModule.forRoot({ envFile: '.env.production' })

B ConfigModule.forRoot({ path: '.env.production' })

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

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

💡 Hint

Check the exact option name for specifying the env file path in ConfigModule.

The correct option to specify a custom environment file path is envFilePath. Other keys like path, env_path, or envFile are invalid and cause errors.

🔧 Debug

advanced

Why does ConfigService.get() return undefined?

You have a .env file with API_KEY=abc123 but calling configService.get('API_KEY') returns undefined. What is the most likely cause?

NestJS

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

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

@Injectable()
export class ApiService {
  constructor(private configService: ConfigService) {}

  getKey() {
    return this.configService.get('API_KEY');
  }
}

A You must call configService.load() before using get().

B The .env file is not in the project root or not loaded properly.

C ConfigService.get() only works for variables starting with NEST_ prefix.

D API_KEY is a reserved keyword and cannot be accessed.

💡 Hint

Check the location and loading of the .env file.

If the .env file is missing or not in the root directory, ConfigModule won't load the variables, so configService.get('API_KEY') returns undefined.

🧠 Conceptual

expert

What is the effect of setting isGlobal: true in ConfigModule.forRoot()?

In a large NestJS app, you use ConfigModule.forRoot({ isGlobal: true }). What does this change in how you use ConfigModule?

A ConfigModule is automatically available in all modules without needing to import it again.

B ConfigModule variables become global environment variables accessible outside the app.

C ConfigModule disables caching of environment variables for every request.

D ConfigModule requires manual import in every module despite isGlobal: true.

💡 Hint

Think about module imports and global scope in NestJS.

Setting isGlobal: true makes the ConfigModule available across the entire app without needing to import it in every module manually.