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.

Practice

1. In NestJS, what does the HTTP status code 201 usually indicate in a response?

easy

A. A new resource was successfully created

B. The request was malformed or invalid

C. The requested resource was not found

D. The server encountered an internal error

Solution

1. Step 1: Understand HTTP status codes

   HTTP status codes communicate the result of a client's request. Code 201 means "Created".

2. Step 2: Match 201 with its meaning

   201 specifically means a new resource was successfully created on the server.

3. Final Answer:

   A new resource was successfully created -> Option A

4. Quick Check:

   201 = Created [OK]

Hint: 201 means resource created successfully [OK]

Common Mistakes:

• Confusing 201 with 404 (not found)
• Thinking 201 means server error
• Mixing 201 with 400 (bad request)

2. Which of the following is the correct way to set a custom header X-Custom-Header with value 123 in a NestJS controller using Express response?

easy

A. res.setHeader('X-Custom-Header', 789);

B. res.set('X-Custom-Header', '123');

C. res.header('X-Custom-Header', '789');

D. res.addHeader('X-Custom-Header', '123');

Solution

1. Step 1: Recall Express response methods

   Express response object uses res.set() to set headers.

2. Step 2: Check method and value types

   res.set() accepts header name and string value. res.set('X-Custom-Header', '123'); uses correct method and string value.

3. Final Answer:

   res.set('X-Custom-Header', '123'); -> Option B

4. Quick Check:

   Use res.set() to set headers [OK]

Hint: Use res.set() to set headers in NestJS [OK]

Common Mistakes:

• Using res.setHeader (not Express method)
• Passing number instead of string as header value
• Using non-existent res.addHeader method

3. What will be the HTTP status code and header in the response when this NestJS controller method runs?

async getData(@Res() res) {
  res.status(204).set('X-Info', 'No Content').send();
}

medium

A. Status 204 with no headers

B. Status 200 with header X-Info: No Content

C. Status 204 with header X-Info: No Content

D. Status 404 with header X-Info: No Content

Solution

1. Step 1: Analyze status and header setting

   The code sets status to 204 and header 'X-Info' to 'No Content'.

2. Step 2: Understand 204 status behavior

   Status 204 means "No Content" and allows custom headers. The header is set correctly.

3. Final Answer:

   Status 204 with header X-Info: No Content -> Option C

4. Quick Check:

   Status 204 + header set = Status 204 with header X-Info: No Content [OK]

Hint: res.status(204).set() sets status and headers [OK]

Common Mistakes:

• Assuming 204 means no headers allowed
• Confusing default status 200 with explicit 204
• Ignoring header set after status

4. Identify the error in this NestJS controller method that tries to set status and headers:

async update(@Res() res) {
  res.status(200);
  res.set('Content-Type', 'application/json');
  res.send({ success: true });
  res.status(201);
}

medium

A. Calling res.status(201) after res.send() has no effect

B. res.set() must be called before res.status()

C. res.send() cannot send JSON objects

D. res.status() cannot be called twice

Solution

1. Step 1: Review response flow

   res.send() sends the response and ends it. Any code after it won't affect response.

2. Step 2: Check status calls order

   Calling res.status(201) after res.send() does nothing because response is already sent.

3. Final Answer:

   Calling res.status(201) after res.send() has no effect -> Option A

4. Quick Check:

   res.send() ends response, later status calls ignored [OK]

Hint: Set status before res.send(), not after [OK]

Common Mistakes:

• Trying to set status after sending response
• Thinking res.send() can't send JSON
• Believing res.set() must come before res.status()

5. You want to send a 202 Accepted status with a custom header X-Request-ID and a JSON body in NestJS. Which code snippet correctly achieves this?

hard

A. res.send({ message: 'Accepted' }).status(202).set('X-Request-ID', requestId);

B. res.set('X-Request-ID', requestId).status(202).send('Accepted');

C. res.status(202).send({ message: 'Accepted' }).set('X-Request-ID', requestId);

D. res.status(202).set('X-Request-ID', requestId).json({ message: 'Accepted' });

Solution

1. Step 1: Order of method calls matters

   In Express, chaining status, set, and json works if status is set before sending.

2. Step 2: Check each option's correctness

   Options A and C call send before completing status/header setup, invalid. res.set('X-Request-ID', requestId).status(202).send('Accepted'); sets header and status but uses res.send('Accepted') sending plain text instead of JSON object. res.status(202).set('X-Request-ID', requestId).json({ message: 'Accepted' }); correctly sets status, header, sends JSON.

3. Step 3: Confirm best practice

   res.status(202).set('X-Request-ID', requestId).json({ message: 'Accepted' }); is the clearest and most common pattern: status, set header, then send JSON.

4. Final Answer:

   res.status(202).set('X-Request-ID', requestId).json({ message: 'Accepted' }); -> Option D

5. Quick Check:

   Status then headers then send JSON [OK]

Hint: Chain status, set, then send/json in that order [OK]

Common Mistakes:

• Calling send before setting status or headers
• Using send instead of json for JSON body
• Setting headers after sending response