NestJS Basic 5

Question 1

What is Middleware in NestJS and when does it execute?

Accepted Answer

A function that runs before the route handler, with access to req and res

Answer

Middleware functions execute before the route handler and can modify the request/response or call next() to pass control forward.

Question 2

Which NestJS feature allows you to execute code before and after the entire application lifecycle?

Accepted Answer

Lifecycle hooks like OnModuleInit and OnApplicationBootstrap

Answer

NestJS lifecycle hooks (OnModuleInit, OnApplicationBootstrap, OnModuleDestroy, etc.) let you run logic at specific points in the app lifecycle.

Question 3

What is the @Res() decorator used for in NestJS?

Accepted Answer

To access the underlying framework's native response object

Answer

@Res() injects the raw Express (or Fastify) response object, giving you full control over the response but bypassing NestJS response handling.

Question 4

In NestJS, what is the purpose of the ConfigModule?

Accepted Answer

To load and manage environment variables and configuration across the application

Answer

ConfigModule (from @nestjs/config) loads .env files and provides a ConfigService to access environment variables throughout the app.

Question 5

When using class-validator with NestJS, which pipe must be globally enabled to trigger validation?

Accepted Answer

ValidationPipe

Answer

ValidationPipe must be applied (globally or per-route) to automatically validate incoming data against class-validator decorated DTOs.

NestJS Practice Test