Error logging strategies in NextJS

Introduction

Error logging helps you find and fix problems in your Next.js app quickly. It keeps track of what went wrong so you can improve your app.

When your Next.js app crashes or shows unexpected behavior.

When you want to know what errors users experience in production.

When debugging new features or changes in your app.

When monitoring app health and performance over time.

Syntax

NextJS

try {
  // code that might fail
} catch (error) {
  console.error('Error message:', error);
}

Use try...catch blocks to catch errors in your code.

console.error() prints error details to the terminal or browser console.

Examples

Catches errors when fetching data from an API and logs them.

NextJS

try {
  const data = await fetch('/api/data');
  const json = await data.json();
} catch (error) {
  console.error('Failed to fetch data:', error);
}

Logs errors in an API route and sends a 500 response.

NextJS

import { NextApiRequest, NextApiResponse } from 'next';

export default function handler(req, res) {
  try {
    // some code that may throw
    res.status(200).json({ message: 'Success' });
  } catch (error) {
    console.error('API error:', error);
    res.status(500).json({ error: 'Internal Server Error' });
  }
}

Logs errors differently based on environment: external service in production, console in development.

NextJS

if (process.env.NODE_ENV === 'production') {
  // send error to external service like Sentry
  Sentry.captureException(error);
} else {
  console.error(error);
}

Sample Program

This Next.js API route fetches data from an external API. If fetching fails, it logs the error and returns a 500 error response.

NextJS

import { NextApiRequest, NextApiResponse } from 'next';

export default async function handler(req, res) {
  try {
    const response = await fetch('https://jsonplaceholder.typicode.com/posts/1');
    if (!response.ok) {
      throw new Error('Network response was not ok');
    }
    const data = await response.json();
    res.status(200).json(data);
  } catch (error) {
    console.error('Fetch error:', error);
    res.status(500).json({ error: 'Failed to load data' });
  }
}

Important Notes

Always log enough details to understand the error but avoid sensitive data.

Use external error tracking tools like Sentry or LogRocket for production apps.

Console logs are helpful during development but may be removed or redirected in production.

Summary

Error logging helps find and fix problems fast.

Use try...catch and console.error() to log errors.

Consider external services for better error tracking in production.

Practice

1. What is the main purpose of error logging in a Next.js application?

easy

A. To speed up the app loading time

B. To reduce the size of the app bundle

C. To increase the app's SEO ranking

D. To catch and record errors for fixing issues later

Solution

1. Step 1: Understand error logging purpose

   Error logging is used to catch errors that happen during app execution.

2. Step 2: Identify why errors are logged

   Logging errors helps developers find and fix problems to improve app stability.

3. Final Answer:

   To catch and record errors for fixing issues later -> Option D

4. Quick Check:

   Error logging purpose = Catch and fix errors [OK]

Hint: Error logging is for catching and fixing problems [OK]

Common Mistakes:

• Confusing error logging with performance optimization
• Thinking error logging improves SEO
• Believing error logging reduces app size

2. Which of the following is the correct syntax to catch and log an error in Next.js using try...catch?

easy

A. try { /* code */ } catch { console.error }

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

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

D. try { /* code */ } catch error { console.log(error) }

Solution

1. Step 1: Review correct try...catch syntax

   The correct syntax uses parentheses around the error variable in catch: catch (error).

2. Step 2: Check logging method

   console.error(error) correctly logs the error object to the console.

3. Final Answer:

   try { /* code */ } catch (error) { console.error(error) } -> Option B

4. Quick Check:

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

Hint: Catch uses parentheses and console.error logs errors [OK]

Common Mistakes:

• Omitting parentheses in catch
• Using console.log instead of console.error
• Incorrect try or catch block syntax

3. What will be the console output when this Next.js code runs and an error occurs?

try {
  throw new Error('Failed to fetch data')
} catch (err) {
  console.error('Error:', err.message)
}

medium

A. Error: Failed to fetch data

B. Failed to fetch data

C. Error: Error: Failed to fetch data

D. undefined

Solution

1. Step 1: Understand the thrown error

   The code throws an Error object with message 'Failed to fetch data'.

2. Step 2: Analyze the catch block output

   console.error prints 'Error:' plus the error message, resulting in 'Error: Failed to fetch data'.

3. Final Answer:

   Error: Failed to fetch data -> Option A

4. Quick Check:

   console.error prints label + error message = Error: Failed to fetch data [OK]

Hint: console.error prints label plus error.message string [OK]

Common Mistakes:

• Confusing error object with error message string
• Expecting double 'Error:' prefix
• Ignoring the label string in console.error

4. Identify the error in this Next.js error logging code:

try {
  const data = await fetchData()
} catch {
  console.error(error)
}

medium

A. Missing error parameter in catch block

B. Using console.error instead of console.log

C. fetchData() should not be awaited

D. try block should not have await

Solution

1. Step 1: Check catch block syntax

   The catch block is missing the error parameter, so 'error' is undefined inside it.

2. Step 2: Understand error usage

   console.error(error) fails because 'error' is not declared; catch must declare it like catch (error).

3. Final Answer:

   Missing error parameter in catch block -> Option A

4. Quick Check:

   Catch needs error parameter to log it [OK]

Hint: Always name error in catch to use it inside [OK]

Common Mistakes:

• Omitting error parameter in catch
• Thinking console.error is wrong here
• Misunderstanding async/await usage

5. In a production Next.js app, which strategy is best for error logging to ensure issues are tracked and fixed efficiently?

hard

A. Disable all error logging to improve performance

B. Only use console.error locally and ignore errors in production

C. Send errors to an external monitoring service and log locally

D. Log errors only in the browser console without server tracking

Solution

1. Step 1: Understand production error logging needs

   In production, errors should be tracked centrally to fix issues quickly.

2. Step 2: Identify best practice

   Sending errors to external services (like Sentry) plus local logging helps monitor and debug effectively.

3. Final Answer:

   Send errors to an external monitoring service and log locally -> Option C

4. Quick Check:

   Production error tracking = external service + local logs [OK]

Hint: Use external services plus local logs in production [OK]

Common Mistakes:

• Ignoring production error tracking
• Disabling logging to save performance
• Logging only in browser without server monitoring