Why caching is central to Next.js - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Next.js caching function.

NextJS

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

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

AuseState

Bcache

CgetServerSideProps

DuseEffect

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing React hooks like useState or useEffect instead of caching.

The cache function from next/cache helps store data to speed up page rendering.

2fill in blank

medium

Complete the code to wrap a function with Next.js caching.

NextJS

export const getData = [1](() => {
  return fetch('https://api.example.com/data');
});

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

Acache

BuseState

CuseEffect

DgetServerSideProps

Attempts:

3 left

💡 Hint

Common Mistakes

Using React hooks which are not for caching in Next.js.

Wrapping the function with cache stores its result to avoid repeated fetching.

3fill in blank

hard

Fix the error in the caching usage by completing the code.

NextJS

const data = await [1]();

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

AgetData

Bcache

CfetchData

DuseEffect

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the cache function instead of the cached function.

You must call the cached function getData to get the cached result.

4fill in blank

hard

Fill the blank to create a cached fetch with revalidation time.

NextJS

export const getData = cache(() => fetch('https://api.example.com/data'), { revalidate: [1] });

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

AstaleWhileRevalidate

Bfalse

C60

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing boolean values with caching strategy names.

The revalidate time sets cache duration in seconds.

5fill in blank

hard

Fill the blanks to create a cached function with a revalidation.

NextJS

export const getUser = cache(async (id) => {
  const res = await fetch(`/api/user/$[1]`);
  return res.json();
}, { revalidate: [2] });

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

Aid

B120

C`user-${id}`

DuserId

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names or static keys.

The function uses id to fetch user data, sets revalidation to 120 seconds. Next.js automatically generates unique cache keys based on the id argument.

Practice

1. Why is caching important in Next.js for website performance?

easy

A. It stores parts of the website to load pages faster.

B. It deletes all data after every page load.

C. It slows down the website to save energy.

D. It disables JavaScript on the page.

Solution

1. Step 1: Understand caching purpose

   Caching saves website parts so they don't need to be rebuilt every time.

2. Step 2: Connect caching to Next.js performance

   Next.js uses caching to serve pages quickly by reusing saved content.

3. Final Answer:

   It stores parts of the website to load pages faster. -> Option A

4. Quick Check:

   Caching = Faster page loads [OK]

Hint: Caching means saving parts to speed up loading [OK]

Common Mistakes:

• Thinking caching deletes data after load
• Believing caching slows down the site
• Confusing caching with disabling JavaScript

2. Which Next.js feature controls how often cached pages update?

easy

A. revalidate

B. getStaticProps

C. useEffect

D. getServerSideProps

Solution

1. Step 1: Identify caching update control

   Next.js uses the revalidate property to set cache refresh timing.

2. Step 2: Differentiate from other features

   getStaticProps fetches data at build time, useEffect runs on client, getServerSideProps fetches on every request.

3. Final Answer:

   revalidate -> Option A

4. Quick Check:

   Cache update timing = revalidate [OK]

Hint: Look for 'revalidate' to set cache refresh time [OK]

Common Mistakes:

• Confusing getStaticProps with cache timing
• Using useEffect for server caching
• Thinking getServerSideProps controls caching

3. What will happen if you set revalidate: 10 in getStaticProps?

medium

A. The page updates on every request.

B. The page updates every 10 seconds after first load.

C. The page never updates after build.

D. The page updates every 10 minutes.

Solution

1. Step 1: Understand revalidate value meaning

   Setting revalidate: 10 means Next.js will refresh the cached page every 10 seconds.

2. Step 2: Compare with other options

   It does not update on every request, never after build, nor every 10 minutes.

3. Final Answer:

   The page updates every 10 seconds after first load. -> Option B

4. Quick Check:

   revalidate: 10 means 10 seconds refresh [OK]

Hint: revalidate number = seconds between cache refresh [OK]

Common Mistakes:

• Thinking revalidate is minutes, not seconds
• Believing page never updates with revalidate
• Confusing revalidate with server-side rendering

4. You set revalidate: '10' (string) instead of 10 (number). What happens?

medium

A. Next.js updates the page every 10 minutes.

B. Next.js treats it as 10 seconds anyway.

C. Next.js ignores revalidate and never updates the page.

D. Next.js throws a type error and fails to build.

Solution

1. Step 1: Check revalidate type requirement

   Next.js expects revalidate as a number, not a string.

2. Step 2: Understand error on wrong type

   Passing a string causes a type error and build failure.

3. Final Answer:

   Next.js throws a type error and fails to build. -> Option D

4. Quick Check:

   revalidate must be number, string causes error [OK]

Hint: Use number type for revalidate, not string [OK]

Common Mistakes:

• Passing string instead of number for revalidate
• Assuming Next.js auto-converts string to number
• Ignoring build errors caused by wrong types

5. You want a page to show fresh data but still load fast. Which caching strategy fits best in Next.js?

hard

A. Disable caching completely.

B. Use getServerSideProps to fetch data on every request.

C. Set revalidate to a low number like 5 seconds.

D. Set revalidate to a very high number like 86400 seconds.

Solution

1. Step 1: Balance freshness and speed

   Low revalidate means data updates often but still uses cache for speed.

2. Step 2: Compare other options

   getServerSideProps fetches every time but is slower; very high revalidate delays updates; disabling cache hurts speed.

3. Final Answer:

   Set revalidate to a low number like 5 seconds. -> Option C

4. Quick Check:

   Low revalidate = fresh + fast [OK]

Hint: Low revalidate balances fresh data and speed [OK]

Common Mistakes:

• Choosing getServerSideProps for speed
• Setting revalidate too high losing freshness
• Disabling cache hurting performance