Why caching is central to Next.js - Performance Evidence

Performance: Why caching is central to Next.js

HIGH IMPACT

Caching in Next.js affects page load speed and reduces server response time by reusing previously generated content.

Serving pages quickly in Next.js

NextJS

export async function getStaticProps() {
  const data = await fetch('https://api.example.com/data');
  const json = await data.json();
  return { props: { json }, revalidate: 60 };
}

// Static generation with incremental static regeneration caches page for 60 seconds

Page is prebuilt and cached, served instantly, and only regenerated periodically.

📈 Performance GainReduces server response time to under 50ms, lowers CPU load, improves LCP

Serving pages quickly in Next.js

NextJS

export async function getServerSideProps() {
  const data = await fetch('https://api.example.com/data');
  const json = await data.json();
  return { props: { json } };
}

// This runs on every request, no caching

Fetching data and rendering on every request causes slow response and high server load.

📉 Performance CostBlocks rendering for 200-500ms per request, increases server CPU usage

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Server-side rendering on every request	N/A	N/A	High due to slow server response	[X] Bad
Static generation with caching	N/A	N/A	Low due to fast server response	[OK] Good

Rendering Pipeline

Next.js caching avoids repeated server-side rendering by serving prebuilt HTML and JSON. This skips expensive data fetching and rendering during the critical rendering path.

→Server Rendering

→Network

→Browser Rendering

⚠️ BottleneckServer Rendering when no cache is used

Core Web Vital Affected

LCP

Caching in Next.js affects page load speed and reduces server response time by reusing previously generated content.

Optimization Tips

1Use static generation with caching to speed up page loads.

2Avoid server-side rendering on every request for better performance.

3Set revalidate times to balance freshness and speed.

Performance Quiz - 3 Questions

What is the main performance benefit of caching pages in Next.js?

A Larger JavaScript bundles

B More frequent server rendering

C Faster page load by serving prebuilt content

D Increased network requests

DevTools: Network

How to check: Open DevTools, go to Network tab, reload page, check response time and if HTML is served from cache or freshly generated

What to look for: Look for fast initial HTML response times under 100ms indicating cached content; slow times indicate no caching

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