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of 44Explain the core building blocks of a Nest.js application.
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The core building blocks are:
- Controllers: Handle incoming requests and return responses
- Services: Contain business logic and are injectable
- Modules: Organize and encapsulate related functionality
- Providers: Classes that can be injected (services, repositories, factories)
- Middleware: Functions that execute before route handlers
- Guards: Determine whether a request should be handled
- Interceptors: Transform data or add extra logic around method execution
- Pipes: Transform and validate input data
- Filters: Handle exceptions and errors
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What are decorators in Nest.js and provide examples?
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Decorators are special functions that add metadata to classes, methods, or properties. They enable Nest.js to understand how to structure and handle different parts of the application.
Common decorators:
@Controller('users') // Defines a controller
@Get() // HTTP GET method
@Post() // HTTP POST method
@Injectable() // Makes class injectable
@Module() // Defines a module
@Param('id') // Route parameter
@Body() // Request body
@Query() // Query parameters
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What is the difference between @Injectable() and @Controller()?
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- @Injectable(): Marks a class as a provider that can be injected into other classes. Used for services, repositories, and other business logic classes.
- @Controller(): Marks a class as a controller that handles HTTP requests. Controllers define API endpoints and route handling logic.
Controllers can have services injected into them, but services are typically not controllers.
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Explain modules in Nest.js and their purpose.
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Modules are classes decorated with @Module() that organize application structure. They group related controllers, services, and other providers together.
@Module({
imports: [DatabaseModule], // Other modules to import
controllers: [UserController], // Controllers in this module
providers: [UserService], // Services/providers in this module
exports: [UserService] // Providers to export for other modules
})
export class UserModule {}
Benefits:
- Encapsulation of functionality
- Clear separation of concerns
- Reusability across applications
- Lazy loading capabilities
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What is middleware in Nest.js and how do you implement it?
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Middleware functions execute before the route handler. They have access to request and response objects and can modify them.
@Injectable()
export class LoggerMiddleware implements NestMiddleware {
use(req: Request, res: Response, next: NextFunction) {
console.log(`${req.method} ${req.url}`);
next();
}
}
// Apply in module
export class AppModule implements NestModule {
configure(consumer: MiddlewareConsumer) {
consumer
.apply(LoggerMiddleware)
.forRoutes('users');
}
}
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What are DTOs and why are they important?
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DTOs (Data Transfer Objects) define the shape of data sent over the network. They provide type safety and validation.
export class CreateUserDto {
@IsString()
@IsNotEmpty()
name: string;
@IsEmail()
email: string;
@IsInt()
@Min(18)
age: number;
}
@Post()
createUser(@Body() createUserDto: CreateUserDto) {
return this.userService.create(createUserDto);
}
Benefits:
- Type safety
- Input validation
- API documentation
- Clear data contracts
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How do you connect to a database in Nest.js?
What is the difference between @Param(), @Query(), and @Body()?
How do you handle configuration in Nest.js?
What are the different HTTP status codes you can return in Nest.js?
How do you implement request/response logging?
What is the purpose of the @Global() decorator?
How does dependency injection work in Nest.js?
What are pipes in Nest.js and when would you use them?
How do guards work in Nest.js?
What are interceptors and provide a use case?
How do you handle exceptions in Nest.js?
How do you implement authentication in Nest.js?
How do you implement custom decorators in Nest.js?
What are the different types of providers in Nest.js?
How do you implement unit testing in Nest.js?
What is the execution order of Nest.js components?
How do you implement caching in Nest.js?
How do you implement file upload in Nest.js?
What is the difference between synchronous and asynchronous providers?
How do you implement rate limiting in Nest.js?
What is the purpose of ExecutionContext?
How do you implement health checks in Nest.js?
What are the different scopes available for providers?
How do you implement WebSocket communication?
How do you implement custom validation pipes?
What is the difference between guards and middleware?
What are the testing utilities provided by Nest.js?
How do you implement request timeouts?
How do you implement API versioning?
How do you implement custom exception filters?
What are microservices in Nest.js?
What are dynamic modules in Nest.js?
What is circular dependency and how do you resolve it?
How do you implement streaming responses?
How do you implement database transactions?
What are the performance optimization techniques in Nest.js?
What is the lifecycle of a Nest.js application?
What are some common security practices in Nest.js?
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Nest.js cheatsheet
NestJS Interview Cheat Sheet
- Summary01
- 1. Introduction & Core Concepts02
- 2. Project Setup03
- 3. Controllers04
- 4. Providers/Services05
- 5. Modules06
- 6. Middleware07
- 7. Guards08
- 8. Interceptors09
- 9. Pipes10
- 10. Exception Filters11
- 11. Database Integration12
- + 6 more inside
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