Cache debugging tools in NextJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Next.js cache debugging tool.

NextJS

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

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

Aunstable_cache

BcacheDebugger

CuseCache

DcacheTool

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent import like 'cacheDebugger'.

Confusing hook names like 'useCache'.

The unstable_cache function is the official Next.js caching tool import.

2fill in blank

medium

Complete the code to wrap a function with Next.js cache debugging.

NextJS

const cachedFunction = [1](() => {
  return fetch('/api/data');
});

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

Aunstable_cache

BcacheDebugger

CuseCache

DcacheWrap

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent function like 'cacheDebugger'.

Trying to use hooks like 'useCache' outside React components.

The unstable_cache function wraps your function to enable caching.

3fill in blank

hard

Fix the error in the cache debugging function call.

NextJS

const data = await unstable_cache(() => fetch('/api/data'), { [1]: 60 });

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

AstaleTime

Btimeout

CcacheTime

Drevalidate

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect option names like 'timeout' or 'cacheTime'.

Confusing cache options with React state options.

The correct option to set cache duration is revalidate in seconds.

4fill in blank

hard

Fill both blanks to create a cache key part and set revalidate time.

NextJS

const cachedData = unstable_cache(fetchData, { keyParts: ["[1]"], revalidate: [2] });

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

A'user-data'

B120

C60

D'cache-key'

Attempts:

3 left

💡 Hint

Common Mistakes

Using numbers as keys or strings as revalidate values.

Mixing up cache key and revalidate values.

Use a descriptive string like 'user-data' as the key part and set revalidate to 60 seconds.

5fill in blank

hard

Fill all three blanks to define a cached fetch with keyParts, revalidate, and tags.

NextJS

const cachedFetch = unstable_cache(fetchData, { keyParts: ["[1]"], revalidate: [2], tags: ["[3]"] });

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

A'api-fetch'

B30

C'api-tag'

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect types for options.

Forgetting to add tags.

Use 'api-fetch' as the key part, set revalidate to 30 seconds, and use 'api-tag' as the tag.

Practice

1. What is the main purpose of cache debugging tools in Next.js applications?

easy

A. To improve the styling of components

B. To manage user authentication

C. To find and fix issues related to stored or cached data

D. To deploy the application to production

Solution

1. Step 1: Understand cache role in Next.js

   Cache stores data temporarily to speed up app performance but can cause stale data issues.

2. Step 2: Identify purpose of debugging tools

   Cache debugging tools help find and fix problems with this stored data to ensure fresh and correct information.

3. Final Answer:

   To find and fix issues related to stored or cached data -> Option C

4. Quick Check:

   Cache debugging = find/fix cache issues [OK]

Hint: Cache debugging = fixing stored data problems [OK]

Common Mistakes:

• Confusing cache debugging with styling or deployment
• Thinking cache debugging manages user login
• Assuming cache debugging improves UI appearance

2. Which of the following is the correct way to use React cache in Next.js for debugging purposes?

easy

A. import { cache } from 'react'; cache(async () => {});

B. import { clearCache } from 'next/cache'; clearCache();

C. import { resetCache } from 'react'; resetCache();

D. import { flushCache } from 'next'; flushCache();

Solution

1. Step 1: Recall React cache API

   React provides a cache function to memoize async functions.

2. Step 2: Match correct import and method

   Only import { cache } from 'react'; cache(async () => {}); is valid syntax for using cache.

3. Final Answer:

   import { cache } from 'react'; cache(async () => {}); -> Option A

4. Quick Check:

   React cache usage = cache(asyncFn) [OK]

Hint: Use React's cache(asyncFn) to memoize [OK]

Common Mistakes:

• Using non-existent functions like clearCache or resetCache
• Importing from wrong modules like 'next/cache'
• Calling methods that do not exist on cache object

3. Given this Next.js code snippet using React cache:

import { cache } from 'react';

const fetchData = cache(async () => {
  console.log('Fetching data');
  return 'data';
});

await fetchData();
await fetchData();

What will be logged to the console?

medium

A. Fetching data
Fetching data

B. Error: cache is not a function

C. No output

D. Fetching data

Solution

1. Step 1: Understand React cache behavior

   React's cache wraps the async function to memoize its result, so it runs only once.

2. Step 2: Analyze console logs

   On first call, 'Fetching data' logs; second call returns cached result without logging.

3. Final Answer:

   Fetching data -> Option D

4. Quick Check:

   cache memoizes function, logs once [OK]

Hint: Cached function logs only once on first call [OK]

Common Mistakes:

• Assuming function runs and logs every call
• Thinking cache is not a function error
• Expecting no output at all

4. You notice stale data in your Next.js app despite clearing React cache with cache.clear(). What is a likely cause?

medium

A. You forgot to restart the Next.js server

B. Browser DevTools cache is not cleared

C. The cache.clear() method does not exist

D. React cache automatically clears on every render

Solution

1. Step 1: Understand cache layers

   Besides React cache, browsers also cache network responses and assets.

2. Step 2: Identify stale data cause

   If browser cache is not cleared, stale data may persist despite clearing React cache.

3. Final Answer:

   Browser DevTools cache is not cleared -> Option B

4. Quick Check:

   Browser cache can cause stale data [OK]

Hint: Clear browser cache in DevTools to fix stale data [OK]

Common Mistakes:

• Assuming cache.clear() does not exist
• Thinking React cache clears every render
• Forgetting to restart server is the cause

5. You want to debug cache issues in a Next.js app that uses React cache and server actions. Which combination of tools and steps is best?

hard

A. Use React's cache.clear(), add console logs in server actions, and clear browser cache

B. Only restart the Next.js server and rely on automatic cache clearing

C. Use browser DevTools network tab without modifying code

D. Disable React cache permanently in production

Solution

1. Step 1: Clear React cache programmatically

   Use cache.clear() to reset cached data in React functions.

2. Step 2: Add console logs in server actions

   Logging helps track when server actions run and cache updates happen.

3. Step 3: Clear browser cache

   Browser cache can hold stale data; clearing it ensures fresh data loads.

4. Final Answer:

   Use React's cache.clear(), add console logs in server actions, and clear browser cache -> Option A

5. Quick Check:

   Combine cache clearing, logging, and browser cache clearing [OK]

Hint: Combine cache.clear(), logs, and browser cache clear [OK]

Common Mistakes:

• Relying only on server restart
• Ignoring browser cache effects
• Disabling cache permanently without debugging