Response modification in NextJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a custom header in a Next.js API route response.

NextJS

export async function GET() {
  const response = new Response('Hello World');
  response.headers.set('[1]', 'application/json');
  return response;
}

Drag options to blanks, or click blank then click option'

AAuthorization

BAccept

CContent-Type

DCache-Control

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Accept' instead of 'Content-Type' will not set the response content type.

Setting 'Authorization' header is for requests, not responses.

The Content-Type header tells the client what type of data is being sent. Here, setting it to application/json indicates JSON data.

2fill in blank

medium

Complete the code to modify the response status code in a Next.js API route.

NextJS

export async function GET() {
  return new Response('Not Found', { status: [1] });
}

Drag options to blanks, or click blank then click option'

A200

B404

C500

D301

Attempts:

3 left

💡 Hint

Common Mistakes

Using 200 means success, which doesn't match the 'Not Found' message.

Using 500 means server error, which is not appropriate here.

The status code 404 means 'Not Found', which matches the response message.

3fill in blank

hard

Fix the error in setting multiple headers in the Next.js response object.

NextJS

export async function GET() {
  const headers = new Headers();
  headers.append('X-Custom-Header', 'value1');
  headers.[1]('X-Another-Header', 'value2');
  return new Response('OK', { headers });
}

Drag options to blanks, or click blank then click option'

Aadd

Binsert

Cpush

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'add' or 'push' causes runtime errors because these methods don't exist on Headers.

Using 'append' again would add multiple values to the same header name.

The Headers object uses set to add or overwrite a header. append adds a new value, but to set a new header, set is correct.

4fill in blank

hard

Fill both blanks to create a JSON response with a custom status code and header.

NextJS

export async function GET() {
  const data = { message: 'Success' };
  return new Response(JSON.stringify(data), { status: [1], headers: { '[2]': 'application/json' } });
}

Drag options to blanks, or click blank then click option'

A200

B404

CContent-Type

DAuthorization

Attempts:

3 left

💡 Hint

Common Mistakes

Using 404 status with a success message is contradictory.

Using 'Authorization' header instead of 'Content-Type' is incorrect here.

Status 200 means success. The header Content-Type tells the client the response is JSON.

5fill in blank

hard

Fill all three blanks to create a Next.js API response with a JSON body, custom header, and status code.

NextJS

export async function GET() {
  const result = { success: true };
  return new Response(JSON.stringify([1]), {
    status: [2],
    headers: { '[3]': 'application/json' }
  });
}

Drag options to blanks, or click blank then click option'

Aresult

B404

CContent-Type

D200

Attempts:

3 left

💡 Hint

Common Mistakes

Using 404 status with a success object is wrong.

Using wrong header names causes clients to misinterpret the data.

The response body is the result object stringified. Status 200 means success. Header Content-Type indicates JSON data.

Practice

1. In Next.js, what does modifying the response headers allow you to do?

easy

A. Change the React component state on the client

B. Control caching and security policies sent to the browser

C. Modify the URL path of the current page

D. Update the database directly from the response

Solution

1. Step 1: Understand response headers role

   Response headers tell the browser how to handle the data, like caching or security rules.

2. Step 2: Identify what modifying headers affects

   Changing headers controls browser behavior, not client state or URLs.

3. Final Answer:

   Control caching and security policies sent to the browser -> Option B

4. Quick Check:

   Headers control browser policies = A [OK]

Hint: Headers control browser rules like caching and security [OK]

Common Mistakes:

• Thinking headers change client-side state
• Confusing headers with URL routing
• Assuming headers update databases

2. Which of the following is the correct way to set a custom header in a Next.js API route response?

easy

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

B. res.headers['X-Custom-Header'] = 'value'

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

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

Solution

1. Step 1: Recall Next.js API response methods

   Next.js uses Node.js response objects where setHeader is the standard method.

2. Step 2: Compare options to Node.js response API

   Only setHeader is a valid method; others are incorrect or undefined.

3. Final Answer:

   res.setHeader('X-Custom-Header', 'value') -> Option A

4. Quick Check:

   Use setHeader to set headers = D [OK]

Hint: Use res.setHeader() to set headers in Next.js API [OK]

Common Mistakes:

• Using res.headers as an object directly
• Calling non-existent methods like header() or addHeader()
• Confusing client-side and server-side APIs

3. What will be the HTTP status code of this Next.js API response?

export default function handler(req, res) {
  res.status(404).json({ error: 'Not found' });
}

medium

A. 500

B. 200

C. 404

D. 302

Solution

1. Step 1: Identify the status method usage

   The code calls res.status(404) to set the HTTP status code to 404.

2. Step 2: Understand the effect of res.status()

   This sets the response status code before sending JSON data.

3. Final Answer:

   404 -> Option C

4. Quick Check:

   res.status(404) sets status code 404 [OK]

Hint: res.status(code) sets HTTP status code [OK]

Common Mistakes:

• Assuming default 200 status without checking code
• Confusing 404 with 500 or redirect codes
• Ignoring the status() method effect

4. Identify the error in this Next.js API route code that tries to modify the response:

export default function handler(req, res) {
  res.status(200);
  res.json({ message: 'Hello' });
  res.setHeader('X-Test', 'value');
}

medium

A. res.json() cannot be used with status()

B. res.status(200) is missing a return statement

C. res.setHeader() should be called after res.json()

D. Headers must be set before sending the response body

Solution

1. Step 1: Review response order rules

   Headers must be set before sending the response body with res.json().

2. Step 2: Identify incorrect header setting

   res.setHeader() is called after res.json(), which is too late to modify headers.

3. Final Answer:

   Headers must be set before sending the response body -> Option D

4. Quick Check:

   Set headers before body = C [OK]

Hint: Set headers before sending response body [OK]

Common Mistakes:

• Setting headers after res.json()
• Thinking res.status() sends response immediately
• Ignoring response flow order

5. You want to add caching headers to a Next.js API response only if the user is authenticated. Which code snippet correctly modifies the response based on this condition?

export default function handler(req, res) {
  const isAuth = req.headers.authorization === 'secret-token';
  // Add caching headers only if authenticated
  ???
  res.status(200).json({ data: 'Secure data' });
}

hard

A. if (isAuth) { res.setHeader('Cache-Control', 'private, max-age=3600'); }

B. if (!isAuth) { res.setHeader('Cache-Control', 'private, max-age=3600'); }

C. res.setHeader('Cache-Control', 'public, max-age=3600');

D. res.status(401).json({ error: 'Unauthorized' });

Solution

1. Step 1: Understand the condition for caching

   Caching headers should be added only if the user is authenticated (isAuth is true).

2. Step 2: Choose the correct conditional header setting

   if (isAuth) { res.setHeader('Cache-Control', 'private, max-age=3600'); } sets caching headers only when isAuth is true, matching the requirement.

3. Final Answer:

   if (isAuth) { res.setHeader('Cache-Control', 'private, max-age=3600'); } -> Option A

4. Quick Check:

   Set cache header only if authenticated = B [OK]

Hint: Use if (isAuth) to conditionally set headers [OK]

Common Mistakes:

• Setting cache headers when not authenticated
• Using public cache instead of private
• Returning 401 without setting headers when required