Why controllers handle incoming requests in NestJS - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Role of Controllers in NestJS

In NestJS, why do controllers handle incoming HTTP requests?

A Because controllers handle background tasks and scheduled jobs.

B Because controllers manage database connections directly without services.

C Because controllers define routes and process client requests to return responses.

D Because controllers are responsible for rendering frontend UI components.

💡 Hint

Think about what part of the app talks directly to the user requests.

Controllers in NestJS map incoming HTTP requests to handler methods. They define routes and process requests to send back responses. They do not manage databases or UI rendering directly.

❓ component_behavior

intermediate

Controller Behavior on Incoming Request

What happens inside a NestJS controller when it receives an HTTP GET request to a defined route?

A The controller automatically updates the database without any method execution.

B The controller method mapped to that route executes and returns a response to the client.

C The controller sends the request directly to the frontend without processing.

D The controller queues the request for later processing and does not respond immediately.

💡 Hint

Consider what a controller method does when a route is called.

When a controller receives a request, it runs the method decorated for that route and returns a response. It does not skip processing or delay responses.

📝 Syntax

advanced

Correct Controller Method Decorator

Which decorator correctly defines a method in a NestJS controller to handle HTTP POST requests to the route '/create'?

A @Get('create')

B @Delete('create')

C @Put('create')

D @Post('create')

💡 Hint

POST requests are used to create resources.

The @Post decorator defines a method to handle HTTP POST requests. Other decorators handle different HTTP verbs.

🔧 Debug

advanced

Why Controller Method Does Not Respond

A NestJS controller method is defined but the client never receives a response. What is a likely cause?

NestJS

  @Get('data')
  getData() {
    const data = this.service.fetchData();
    // Missing return statement
  }

A The method does not return the data, so no response is sent.

B The route decorator is incorrect and does not match the request.

C The controller class is missing the @Controller decorator.

D The service method fetchData() throws an error that is not caught.

💡 Hint

Check if the method sends back data to the client.

If the controller method does not return a value, NestJS cannot send a response, causing the client to wait indefinitely.

❓ lifecycle

expert

Controller Lifecycle and Request Handling

In NestJS, how often is a controller instance created to handle incoming HTTP requests by default?

A A single controller instance is created and shared for all requests (singleton).

B A new controller instance is created for each incoming request.

C Controllers are created once per user session and reused.

D Controllers are created only once when the server starts and never recreated.

💡 Hint

Think about how NestJS manages controller instances for performance.

By default, NestJS creates a single instance of each controller (singleton) that handles all requests. This improves performance and resource use.