Server-side error handling in NextJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the error handling function from Next.js.

NextJS

import { [1] } from 'next/server';

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

ANextResponse

Bredirect

Cerror

DNextError

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'error' which is not a valid import from 'next/server'.

Confusing 'redirect' with error handling.

Trying to import 'NextError' which does not exist.

The NextResponse object is imported from 'next/server' to handle responses including errors on the server side.

2fill in blank

medium

Complete the code to return a 404 error with a message in a Next.js server function.

NextJS

return new [1]('Not Found', { status: 404 });

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

AError

BNextResponse

CResponse

DNextError

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Error' which does not set HTTP status codes directly.

Using 'NextResponse' with a constructor that does not exist.

Using 'NextError' which is not a valid Next.js class.

Returning a new Response with a status code is the standard way to handle server-side errors in Next.js. NextResponse is used for additional Next.js features but does not support this constructor signature.

3fill in blank

hard

Fix the error in this server function to correctly catch and handle errors.

NextJS

export async function GET() {
  try {
    const data = await fetchData();
    return NextResponse.json(data);
  } catch (error) {
    return new [1]('Server Error', { status: 500 });
  }
}

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

AError

BResponse

CNextResponse

DNextError

Attempts:

3 left

💡 Hint

Common Mistakes

Returning 'Error' which is not a response object.

Using 'NextError' which does not exist.

Using 'NextResponse' with a constructor that does not exist.

To return an error response in Next.js server functions, you create a new Response with the error message and status code. NextResponse does not support this constructor signature.

4fill in blank

hard

Fill both blanks to create a JSON error response with status 400 in a Next.js server function.

NextJS

return NextResponse.[1]({ error: 'Bad Request' }, { status: [2] });

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

Ajson

Btext

C400

D500

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'text' instead of 'json' to send JSON data.

Using status 500 which means server error, not bad request.

Omitting the status code.

The NextResponse.json method sends a JSON response, and the status code 400 indicates a bad request error.

5fill in blank

hard

Fill all three blanks to handle a missing parameter error and return a JSON response with status 422.

NextJS

if (!params.id) {
  return NextResponse.[1]({ message: 'ID is required' }, { status: [2] });
}

throw new [3]('Unexpected error');

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

Ajson

B422

CResponse

DError

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Response' instead of 'json' to send JSON data.

Using status 400 or 500 instead of 422.

Throwing 'Response' instead of 'Error' for exceptions.

Use NextResponse.json to send JSON data, status 422 means unprocessable entity, and Error is thrown for unexpected errors.

Practice

1. What is the main purpose of using try...catch blocks in Next.js server-side functions?

easy

A. To style components dynamically

B. To catch and handle errors gracefully during server-side execution

C. To improve client-side rendering speed

D. To manage user authentication on the client

Solution

1. Step 1: Understand server-side error handling

   Server-side functions can fail due to unexpected issues. Using try...catch helps catch these errors.

2. Step 2: Purpose of try...catch

   The try block runs code that might fail, and the catch block handles errors to prevent crashes and provide feedback.

3. Final Answer:

   To catch and handle errors gracefully during server-side execution -> Option B

4. Quick Check:

   Error handling = catch errors gracefully [OK]

Hint: Try-catch blocks catch errors on the server side [OK]

Common Mistakes:

• Confusing client-side and server-side error handling
• Thinking try-catch improves UI styling
• Assuming try-catch speeds up rendering

2. Which of the following is the correct syntax to catch errors in a Next.js server function?

easy

A. try { /* code */ } handle (error) { /* handle error */ }

B. catch { /* code */ } try (error) { /* handle error */ }

C. try { /* code */ } catch (error) { /* handle error */ }

D. try: { /* code */ } except (error) { /* handle error */ }

Solution

1. Step 1: Recall JavaScript error handling syntax

   The correct syntax uses try { ... } catch (error) { ... } to catch errors.

2. Step 2: Identify correct option

   try { /* code */ } catch (error) { /* handle error */ } matches the correct syntax. Other options use invalid keywords or order.

3. Final Answer:

   try { /* code */ } catch (error) { /* handle error */ } -> Option C

4. Quick Check:

   Correct try-catch syntax = try { /* code */ } catch (error) { /* handle error */ } [OK]

Hint: Remember: try then catch with parentheses [OK]

Common Mistakes:

• Using incorrect keywords like except or handle
• Swapping try and catch blocks
• Omitting parentheses after catch

3. Consider this Next.js server function snippet:

export async function GET() {
  try {
    throw new Error('Failed to fetch data');
  } catch (error) {
    return new Response(error.message, { status: 500 });
  }
}

What will be the HTTP status code returned when this function runs?

medium

A. 400

B. 404

C. 200

D. 500

Solution

1. Step 1: Analyze the thrown error

   The function throws an error with message 'Failed to fetch data'.

2. Step 2: Check the catch block response

   The catch block returns a Response with status 500, indicating a server error.

3. Final Answer:

   500 -> Option D

4. Quick Check:

   Server error status code = 500 [OK]

Hint: Error caught returns status 500 by default [OK]

Common Mistakes:

• Assuming status 200 despite error
• Confusing 404 (not found) with server error
• Ignoring the status property in Response

4. Identify the error in this Next.js server function code:

export async function GET() {
  try {
    const data = await fetch('https://api.example.com/data');
    return new Response(JSON.stringify(data));
  } catch (error) {
    return new Response('Error occurred', { status: 500 });
  }
}

medium

A. Not parsing fetch response to JSON before stringifying

B. Missing await on fetch call

C. Incorrect status code in catch block

D. No error handling implemented

Solution

1. Step 1: Understand fetch response handling

   The fetch call returns a Response object, not the actual data. We must call response.json() to parse it.

2. Step 2: Identify missing JSON parsing

   The code stringifies the Response object directly without parsing JSON, which is incorrect.

3. Final Answer:

   Not parsing fetch response to JSON before stringifying -> Option A

4. Quick Check:

   Parse response.json() before JSON.stringify() [OK]

Hint: Always parse fetch response with .json() before use [OK]

Common Mistakes:

• Stringifying the Response object directly
• Forgetting to await response.json()
• Assuming fetch returns JSON data directly

5. You want to create a Next.js server function that fetches user data and returns a 404 status if the user is not found, or a 500 status if the fetch fails. Which code snippet correctly implements this error handling?

hard

A. export async function GET() {
try {
const res = await fetch('https://api.example.com/user');
if (!res.ok) {
if (res.status === 404) return new Response('User not found', { status: 404 });
throw new Error('Fetch failed');
}
const user = await res.json();
return new Response(JSON.stringify(user));
} catch {
return new Response('Server error', { status: 500 });
}
}

B. export async function GET() {
const res = await fetch('https://api.example.com/user');
if (res.status === 404) return new Response('User not found', { status: 404 });
const user = await res.json();
return new Response(JSON.stringify(user));
}

C. export async function GET() {
try {
const user = await fetch('https://api.example.com/user').json();
return new Response(JSON.stringify(user));
} catch (error) {
return new Response('User not found', { status: 404 });
}
}

D. export async function GET() {
try {
const res = await fetch('https://api.example.com/user');
const user = await res.json();
return new Response(JSON.stringify(user));
} catch {
return new Response('User not found', { status: 404 });
}
}

Solution

1. Step 1: Check for HTTP errors explicitly

   export async function GET() { try { const res = await fetch('https://api.example.com/user'); if (!res.ok) { if (res.status === 404) return new Response('User not found', { status: 404 }); throw new Error('Fetch failed'); } const user = await res.json(); return new Response(JSON.stringify(user)); } catch { return new Response('Server error', { status: 500 }); } } checks res.ok and handles 404 with a specific response, throwing errors for other failures.

2. Step 2: Use try-catch for fetch failures

   The catch block returns a 500 status for server errors, correctly distinguishing error types.

3. Final Answer:

   Correctly handles 404 if the user is not found and 500 if the fetch fails -> Option A

4. Quick Check:

   Check res.ok and catch errors for 404 and 500 [OK]

Hint: Check res.ok and catch errors separately for 404 and 500 [OK]

Common Mistakes:

• Not checking res.ok before parsing JSON
• Returning 404 inside catch block incorrectly
• Assuming fetch throws on 404 automatically