Error logging strategies in NextJS - Mini Project: Build & Apply

Error Logging Strategies in Next.js

📖 Scenario: You are building a Next.js web application that needs to track errors effectively. Proper error logging helps developers find and fix problems quickly, improving user experience.

🎯 Goal: Learn how to set up basic error logging in a Next.js app by creating an error log array, configuring a log level, capturing errors during rendering, and displaying the logged errors.

📋 What You'll Learn

Create an array called errorLogs to store error messages

Add a configuration variable logLevel to control logging detail

Write a function logError that adds errors to errorLogs only if the logLevel allows it

Simulate an error and log it using logError

Display the logged errors in the console

💡 Why This Matters

🌍 Real World

Error logging helps developers quickly find and fix bugs in web applications, improving reliability and user satisfaction.

💼 Career

Understanding error logging is essential for roles like DevOps engineer, site reliability engineer, and frontend/backend developer to maintain healthy applications.

1

Create the error log storage

Create an empty array called errorLogs to store error messages.

NextJS

// Create an empty array called errorLogs
// Your code here

Hint

Use const errorLogs = []; to create an empty array.

2

Add a log level configuration

Add a constant called logLevel and set it to the string "error" to control which errors get logged.

NextJS

const errorLogs = [];
// Add a constant logLevel set to "error"
// Your code here

Hint

Use const logLevel = "error"; to set the logging level.

3

Create the error logging function

Write a function called logError that takes a parameter message. Inside the function, check if logLevel is "error". If yes, add the message to the errorLogs array.

NextJS

const errorLogs = [];
const logLevel = "error";
// Write function logError(message) that adds message to errorLogs if logLevel is "error"
// Your code here

Hint

Use an if statement inside logError to check logLevel before pushing the message.

4

Simulate and display logged errors

Call logError with the string "Page failed to load". Then, use console.log to display the errorLogs array.

NextJS

const errorLogs = [];
const logLevel = "error";
function logError(message) {
    if (logLevel === "error") {
        errorLogs.push(message);
    }
}
// Call logError with "Page failed to load" and print errorLogs
// Your code here

Hint

Call logError("Page failed to load") and then console.log(errorLogs) to see the logged errors.

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