Fetch caching behavior in NextJS - Performance & Optimization

Performance: Fetch caching behavior

MEDIUM IMPACT

This affects how quickly data loads on the page and how often the browser or server fetches data again.

Fetching data on page load with caching

NextJS

const res = await fetch('/api/data', { cache: 'force-cache' });
const data = await res.json();

Uses cached response if available, reducing network requests and speeding up load.

📈 Performance Gainreduces network requests, improves LCP by loading data faster

Fetching data on page load with caching

NextJS

const res = await fetch('/api/data', { cache: 'no-store' });
const data = await res.json();

This disables caching, causing a new network request on every page load, slowing down load time.

📉 Performance Costblocks rendering for every request, increases network latency

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Fetch with no-store cache	Minimal	0	Low	[X] Bad
Fetch with force-cache	Minimal	0	Low	[OK] Good

Rendering Pipeline

Fetch caching affects the network request stage before rendering. Cached data can skip network delays, speeding up style calculation and layout.

→Network Request

→Style Calculation

→Layout

→Paint

⚠️ BottleneckNetwork Request

Core Web Vital Affected

LCP

This affects how quickly data loads on the page and how often the browser or server fetches data again.

Optimization Tips

1Use 'force-cache' or default caching to speed up repeated fetches.

2Avoid 'no-store' unless fresh data is critical every time.

3Check network tab to confirm caching behavior and reduce redundant requests.

Performance Quiz - 3 Questions

What is the main benefit of using fetch caching in Next.js?

A Reduces network requests and speeds up page load

B Increases the number of network requests

C Blocks rendering until all data is fetched

D Disables browser cache completely

DevTools: Network

How to check: Open DevTools, go to Network tab, reload page, and observe if fetch requests are served from cache (status 200 from disk cache or 304).

What to look for: Look for fewer network requests and faster response times indicating effective caching.

Practice

1. In Next.js, what does setting cache: "force-cache" in a fetch call do?

easy

A. It returns cached data if available, otherwise fetches from the network.

B. It always fetches fresh data from the network, ignoring cache.

C. It disables caching completely for the fetch request.

D. It caches the response only for the current session.

Solution

1. Step 1: Understand the cache option "force-cache"

   This option tells Next.js to use cached data if it exists, avoiding a network request.

2. Step 2: Behavior when cache is missing

   If no cached data is found, it fetches fresh data and caches it for future use.

3. Final Answer:

   It returns cached data if available, otherwise fetches from the network. -> Option A

4. Quick Check:

   force-cache = use cache first [OK]

Hint: force-cache means use cache if present, else fetch fresh [OK]

Common Mistakes:

• Confusing force-cache with no-store which disables cache
• Thinking force-cache always fetches fresh data
• Assuming force-cache caches only for session

2. Which of the following is the correct syntax to fetch data with no caching in Next.js?

easy

A. fetch(url, { cache: "force-cache" })

B. fetch(url, { cache: "default" })

C. fetch(url, { cache: "reload" })

D. fetch(url, { cache: "no-store" })

Solution

1. Step 1: Identify the option for no caching

   The no-store cache mode disables caching and always fetches fresh data.

2. Step 2: Verify syntax correctness

   The syntax fetch(url, { cache: "no-store" }) is valid and correctly disables cache.

3. Final Answer:

   fetch(url, { cache: "no-store" }) -> Option D

4. Quick Check:

   no-store disables cache [OK]

Hint: Use cache: "no-store" to disable caching [OK]

Common Mistakes:

• Using "reload" which is not a valid cache option in Next.js fetch
• Confusing "force-cache" with no caching
• Omitting the cache option entirely

3. What will be the behavior of this Next.js fetch call?

await fetch('/api/data', { cache: 'no-cache' })

medium

A. Returns cached data if available, but revalidates in background.

B. Always fetches fresh data and updates the cache.

C. Ignores cache and never stores the response.

D. Fetches from cache only, never from network.

Solution

1. Step 1: Understand the 'no-cache' mode

   This mode returns cached data if available but triggers a background fetch to update the cache.

2. Step 2: Confirm behavior in Next.js fetch

   Next.js uses this to balance speed and freshness by serving cache immediately and updating it asynchronously.

3. Final Answer:

   Returns cached data if available, but revalidates in background. -> Option A

4. Quick Check:

   no-cache = cache then revalidate [OK]

Hint: no-cache serves cache then refreshes in background [OK]

Common Mistakes:

• Thinking no-cache disables cache completely
• Assuming no-cache never uses cached data
• Confusing no-cache with no-store

4. You wrote this fetch call in Next.js:

fetch('/api/data', { cache: 'reload' })

But it throws an error. What is the problem?

medium

A. You must use async/await with fetch.

B. You forgot to add method: 'GET' in options.

C. "reload" is not a valid cache option in Next.js fetch.

D. The URL must be absolute, not relative.

Solution

1. Step 1: Check valid cache options in Next.js

   Next.js fetch supports "force-cache", "no-store", "no-cache", and "default" but not "reload".

2. Step 2: Identify error cause

   Using "reload" causes a syntax or runtime error because it's unsupported.

3. Final Answer:

   "reload" is not a valid cache option in Next.js fetch. -> Option C

4. Quick Check:

   Invalid cache option = error [OK]

Hint: Check cache option spelling and validity [OK]

Common Mistakes:

• Assuming reload is valid from browser fetch API
• Ignoring error messages about invalid options
• Thinking method or URL causes this error

5. You want to fetch user data in Next.js and ensure it is always fresh but also want to avoid unnecessary network requests if the data was fetched less than 10 seconds ago. Which caching strategy should you use?

hard

A. Use cache: 'no-store' and implement a custom timer to refetch every 10 seconds.

B. Use cache: 'no-cache' with next: { revalidate: 10 } option.

C. Use cache: 'force-cache' with next: { revalidate: 10 } option.

D. Use cache: 'default' without revalidation.

Solution

1. Step 1: Understand requirement for freshness and caching

   You want fresh data but avoid fetching more than once every 10 seconds.

2. Step 2: Analyze caching options

   cache: 'no-cache' serves cached data but revalidates in background; next: { revalidate: 10 } tells Next.js to re-fetch after 10 seconds.

3. Step 3: Compare with other options

   no-store disables cache completely, forcing fetch every time; force-cache caches indefinitely; default has no revalidation control.

4. Final Answer:

   Use cache: 'no-cache' with next: { revalidate: 10 } option. -> Option B

5. Quick Check:

   no-cache + revalidate = fresh every 10s [OK]

Hint: Combine no-cache with revalidate for timed freshness [OK]

Common Mistakes:

• Using no-store causes always fresh but no caching
• Using force-cache ignores revalidate timing
• Forgetting to add revalidate option