ConfigModule setup in NestJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this ConfigModule setup code?

Consider this NestJS module setup using ConfigModule. What will be the value of configService.get('APP_NAME') inside AppService?

NestJS

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

@Module({
  imports: [
    ConfigModule.forRoot({
      isGlobal: true,
      load: [() => ({ APP_NAME: 'NestApp' })],
    }),
  ],
  providers: [
    {
      provide: 'APP_SERVICE',
      useFactory: (configService: ConfigService) => {
        return { appName: configService.get('APP_NAME') };
      },
      inject: [ConfigService],
    },
  ],
  exports: ['APP_SERVICE'],
})
export class AppModule {}

A null

B 'NestApp'

C undefined

D Throws error: ConfigService not found

💡 Hint

Remember that ConfigModule.forRoot with isGlobal: true makes the config available everywhere.

The ConfigModule is set as global and loads a config object with APP_NAME set to 'NestApp'. The ConfigService can access this value anywhere, so configService.get('APP_NAME') returns 'NestApp'.

📝 Syntax

intermediate

Which option correctly imports ConfigModule with environment variable support?

You want to load environment variables from a custom file .env.dev using ConfigModule. Which code snippet correctly sets this up?

A ConfigModule.forRoot({ envPath: '.env.dev' })

B ConfigModule.forRoot({ envFile: '.env.dev' })

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

D ConfigModule.forRoot({ envFilePaths: ['.env.dev'] })

💡 Hint

Check the exact property name for specifying environment file path in ConfigModule options.

The correct option is envFilePath. This tells ConfigModule to load environment variables from the specified file.

🔧 Debug

advanced

Why does ConfigService return undefined for a variable?

Given this setup, why does configService.get('DATABASE_URL') return undefined? Code: import { Module } from '@nestjs/common'; import { ConfigModule } from '@nestjs/config'; @Module({ imports: [ConfigModule.forRoot()], }) export class AppModule {} And the environment file .env contains: DATABASE_URL=postgres://user:pass@localhost/db But configService.get('DATABASE_URL') returns undefined.

A ConfigService requires manual injection to work

B ConfigModule.forRoot() requires explicit envFilePath to load .env

C DATABASE_URL is not a valid environment variable name

D The .env file is not in the root directory where the app runs

💡 Hint

Check where the app expects the .env file to be located.

By default, ConfigModule looks for .env in the current working directory. If the .env file is elsewhere, variables won't load, causing undefined results.

❓ state_output

advanced

What is the output of this ConfigModule async setup?

Consider this async configuration setup for ConfigModule. What will configService.get('API_KEY') return? Code: import { Module } from '@nestjs/common'; import { ConfigModule, ConfigService } from '@nestjs/config'; @Module({ imports: [ ConfigModule.forRoot({ isGlobal: true, load: [async () => { return new Promise(resolve => { setTimeout(() => resolve({ API_KEY: '12345' }), 100); }); }], }), ], }) export class AppModule {}

A undefined

B '12345'

C Promise { <pending> }

D Throws error: Async load not supported

💡 Hint

Check if ConfigModule supports async functions in load array.

ConfigModule's load expects synchronous functions returning config objects. Async functions return promises, so config keys are not set, resulting in undefined.

🧠 Conceptual

expert

Which option correctly explains ConfigModule global behavior?

You want to use ConfigService in multiple modules without importing ConfigModule repeatedly. Which statement about ConfigModule.forRoot({ isGlobal: true }) is true?

A It registers ConfigModule once globally, so all modules can inject ConfigService without importing ConfigModule again

B It requires importing ConfigModule in every module to access ConfigService despite isGlobal: true

C It disables ConfigService injection to force manual config passing

D It only works if ConfigModule is imported in the root module explicitly

💡 Hint

Think about what 'global' means in NestJS modules.

Setting isGlobal: true makes ConfigModule available everywhere automatically, so you don't need to import it in every module to use ConfigService.