NestJS Answers

Basic NestJS Answers

#	Question	Answer	Examples
1	What is NestJS?	A progressive Node.js framework for building efficient, scalable server-side applications	Inspired by Angular, uses TypeScript by default
2	Why use NestJS?	Provides structure, modularity, and maintainability for Node.js applications	Encourages best practices, dependency injection, decorators, CLI tools
3	What is a Module?	A fundamental building block in NestJS; groups related components	@Module({ controllers: [], providers: [] }) export class AppModule {}
4	What is a Controller?	A class that handles incoming requests and returns responses	@Controller('users') export class UsersController { ... }
5	What is a Provider?	A class that encapsulates logic and can be injected (often services)	@Injectable() export class UsersService { ... }
6	What is a Decorator?	A special syntax that adds metadata to classes, methods, properties, etc.	@Controller(), @Injectable(), @Get(), @Post(), @Module()
7	What is Dependency Injection (DI)?	A design pattern where a framework "injects" dependencies into components	constructor(private readonly usersService: UsersService) {}
8	How do you create a new NestJS project?	Using the Nest CLI	nest new my-app
9	How do you generate a Controller?	Using the Nest CLI	nest generate controller users
10	How do you generate a Service?	Using the Nest CLI	nest generate service users
11	What is the @Get() decorator?	Defines a route handler for HTTP GET requests	@Get() findAll(): string { ... }
12	What is the @Post() decorator?	Defines a route handler for HTTP POST requests	@Post() create(@Body() createUserDto: CreateUserDto) { ... }
13	What is the @Body() decorator?	Extracts parameters from the request body	@Post() create(@Body() createUserDto: CreateUserDto) { ... }
14	What is the @Param() decorator?	Extracts route parameters from the URL	@Get(':id') findOne(@Param('id') id: string) { ... }
15	What is the @Query() decorator?	Extracts query parameters from the URL	@Get() findAll(@Query('name') name: string) { ... }

Intermediate NestJS Answers

#	Question	Answer	Examples
1	What is the imports array in a Module?	Specifies other modules that the current module needs to use	@Module({ imports: [HttpModule] }) export class UsersModule {}
2	What is the providers array in a Module?	Lists services or other providers that are created and managed by the module	@Module({ providers: [UsersService] }) export class UsersModule {}
3	What is the exports array in a Module?	Specifies providers that should be made available for use in other modules	@Module({ providers: [UsersService], exports: [UsersService] }) export class UsersModule {}
4	What is a DTO (Data Transfer Object)?	A class or interface for transferring data between layers (e.g., controller to service)	class CreateUserDto { name: string; email: string; }
5	What are Pipes?	Functions that transform incoming data before it's handled by a route handler	@UsePipes(new ValidationPipe()) @Post() create(@Body() createUserDto: CreateUserDto) { ... }
6	What are Guards?	Functions that determine whether a route handler should be executed (authorization)	@UseGuards(AuthGuard) @Get('profile') getProfile() { ... }
7	What are Interceptors?	Functions that intercept incoming requests and outgoing responses, allowing modification or logging	@UseInterceptors(LoggingInterceptor) @Get() findAll() { ... }
8	What are Exception Filters?	Functions that catch unhandled exceptions and provide a consistent error response	@UseFilters(new HttpExceptionFilter()) @Get('error') getError() { ... }
9	What is the Scope of a provider?	Defines the lifecycle of a provider instance (e.g., Singleton, Request)	@Injectable({ scope: Scope.REQUEST }) export class RequestScopedService { ... }
10	What is the HttpModule?	A built-in module for making HTTP requests (e.g., to external APIs)	@Module({ imports: [HttpModule] }) export class DataModule {}
11	What is the HttpService?	The service provided by HttpModule for making HTTP requests	constructor(private readonly httpService: HttpService) {}
12	How do you handle environment variables in NestJS?	Using the ConfigModule from @nestjs/config	@Module({ imports: [ConfigModule.forRoot()] }) export class AppModule {}
13	What is the ConfigModule?	A built-in module for managing configuration settings	@Module({ imports: [ConfigModule.forRoot()] }) export class AppModule {}
14	What is the ConfigService?	The service provided by ConfigModule to access configuration values	constructor(private readonly configService: ConfigService) {}
15	What is the concept of Microservices in NestJS?	Building applications as small, independent services that communicate over a network	Using @nestjs/microservices with transport layers like TCP, RabbitMQ, Kafka, gRPC

Advanced NestJS Answers

#	Question	Answer	Examples
1	What is the ValidationPipe?	A built-in pipe for validating incoming request data based on types (e.g., DTOs)	@UsePipes(new ValidationPipe()) @Post(...)
2	What is ClassSerializerInterceptor?	A built-in interceptor for transforming class instances into plain JSON objects	@UseInterceptors(new ClassSerializerInterceptor(app.get(Reflector)))
3	What is NestFactory?	Provides methods to create a Nest application instance	const app = await NestFactory.create(AppModule);
4	What is the Reflector?	Used to retrieve metadata attached to classes or methods (e.g., for Guards, Interceptors)	constructor(private reflector: Reflector) {}
5	How do you implement authentication in NestJS?	Using Passport (e.g., passport-local, passport-jwt) and Guards (e.g., AuthGuard('jwt'))	@Module({ imports: [PassportModule, JwtModule.register({...})] }) and @UseGuards(AuthGuard('jwt')) @Get('profile')
6	What is a WebSocket Gateway?	A class that handles WebSocket connections and real-time communication	@WebSocketGateway() export class MyGateway { ... }
7	What is the @SubscribeMessage() decorator?	Defines a handler for specific WebSocket message events	@SubscribeMessage('events') handleEvent(@MessageBody() data: string) { ... }
8	How do you handle database connections in NestJS?	Using ORMs like TypeORM, Sequelize, Mongoose, or direct database drivers	@Module({ imports: [TypeOrmModule.forRoot(...), TypeOrmModule.forFeature([User])] })
9	What is TypeOrmModule?	A NestJS module that integrates with TypeORM, an Object-Relational Mapper	@Module({ imports: [TypeOrmModule.forRoot(...)] })
10	What is MongooseModule?	A NestJS module that integrates with Mongoose, an ODM (Object Data Modeling) library	@Module({ imports: [MongooseModule.forRoot(...), MongooseModule.forFeature([{ name: User.name, schema: UserSchema }])] })
11	What is the concept of a "Factory Provider"?	A provider that wraps a dependency that is not a custom class (e.g., from a third-party library)	@Module({ providers: [{ provide: 'Logger', useFactory: () => createLogger() }] })
12	What is a Global Module?	A module whose providers are automatically available in all other modules without explicit import	@Global() @Module({ providers: [SharedService] }) export class SharedModule {}
13	How do you handle logging in NestJS?	Using the built-in Logger class or integrating with libraries like Winston or Pino	private readonly logger = new Logger(MyClass.name); logger.log('message');
14	What is the purpose of CommandModule?	Allows creating command-line interfaces using NestJS	@nestjs/command
15	How do you deploy a NestJS application?	Using platforms like Docker, Heroku, AWS, Google Cloud, Vercel, Netlify	Building the application (npm run build), creating a Docker image, deploying to a cloud provider.