Status codes and headers in NestJS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What status code and header does this NestJS controller send?

Consider this NestJS controller method. What status code and header will the client receive?

NestJS

import { Controller, Get, Res, HttpStatus } from '@nestjs/common';
import { Response } from 'express';

@Controller('test')
export class TestController {
  @Get()
  getData(@Res() res: Response) {
    res.status(HttpStatus.CREATED).set('X-Custom-Header', 'NestJS').json({ message: 'Created' });
  }
}

A Status code 201 with no custom headers and JSON body { message: 'Created' }

B Status code 200 with header 'X-Custom-Header: NestJS' and JSON body { message: 'Created' }

C Status code 201 with header 'X-Custom-Header: NestJS' and JSON body { message: 'Created' }

D Status code 200 with no custom headers and JSON body { message: 'Created' }

💡 Hint

Look at the status() and set() methods on the response object.

The method sets the status code to 201 (Created) using HttpStatus.CREATED. It also sets a custom header 'X-Custom-Header' with value 'NestJS'. The JSON body contains the message.

📝 Syntax

intermediate

Which option correctly sets a 404 status with a custom header in NestJS?

You want to send a 404 Not Found status with a header 'X-Error: NotFound'. Which code snippet is correct?

A res.status(404).set('X-Error', 'NotFound').send('Not Found');

B res.status(HttpStatus.NOT_FOUND).header('X-Error', 'NotFound').send('Not Found');

C res.status(HttpStatus.NOT_FOUND).setHeader('X-Error', 'NotFound').send('Not Found');

D res.status(404).setHeaders('X-Error', 'NotFound').send('Not Found');

💡 Hint

Check the Express Response methods used in NestJS.

The Express Response object uses set() to set headers, not header(), setHeader(), or setHeaders(). Also, HttpStatus.NOT_FOUND is valid but header() is not a method.

🔧 Debug

advanced

Why does this NestJS controller not send the custom header?

This controller method tries to send a custom header but it does not appear in the response. Why?

NestJS

import { Controller, Get, Res } from '@nestjs/common';
import { Response } from 'express';

@Controller('debug')
export class DebugController {
  @Get()
  sendHeader(@Res() res: Response) {
    res.set('X-Debug', 'true');
    return { success: true };
  }
}

A Because the controller method must be async to set headers properly.

B Because 'set' is not a valid method to set headers on the response object.

C Because the header name 'X-Debug' is reserved and ignored by browsers.

D Because returning an object bypasses the manual response, so headers set on res are ignored.

💡 Hint

Think about how NestJS handles @Res() and returned values.

When you use @Res() and also return a value, NestJS ignores the manual response methods like res.set(). You must either use res.send() or return the value but not both.

❓ state_output

advanced

What headers and status code are sent by this NestJS interceptor?

Given this interceptor that modifies the response, what headers and status code will the client receive?

NestJS

import { Injectable, NestInterceptor, ExecutionContext, CallHandler } from '@nestjs/common';
import { Observable, map } from 'rxjs';

@Injectable()
export class HeaderInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
    const response = context.switchToHttp().getResponse();
    response.status(202);
    response.set('X-Intercepted', 'yes');
    return next.handle().pipe(
      map(data => ({ ...data, intercepted: true }))
    );
  }
}

A Status code 202 with header 'X-Intercepted: yes' and JSON body including intercepted: true

B Status code 200 with header 'X-Intercepted: yes' and original JSON body

C Status code 202 with no custom headers and JSON body including intercepted: true

D Status code 200 with no custom headers and original JSON body

💡 Hint

Look at how the interceptor sets status and headers before passing control.

The interceptor sets the status code to 202 and adds the header 'X-Intercepted'. It also modifies the response body to include intercepted: true.

🧠 Conceptual

expert

Which statement about setting status codes and headers in NestJS is true?

Choose the correct statement about how NestJS handles status codes and headers when using @Res() and returning values.

A NestJS automatically merges headers set by res.set() with headers from returned objects, so both are always sent.

B If you use @Res() and call res.status() and res.set(), you must not return a value from the method or NestJS will ignore the manual response.

C You can only set status codes using decorators like @HttpCode; res.status() is ignored in NestJS.

D Headers set in middleware are overwritten by headers set in controllers, so middleware headers never reach the client.

💡 Hint

Think about how NestJS handles manual response control with @Res().

When you inject the response object with @Res() and use it to set status or headers, you must send the response manually and not return a value. Returning a value causes NestJS to ignore the manual response calls.