Fetch caching behavior in NextJS - Step-by-Step Execution

Concept Flow - Fetch caching behavior

Start Fetch Request

↓

Check Cache for URL

↓

Return Cached

↓

Use Cached

↓

Store in Cache

↓

Use Response

↓

End

This flow shows how a fetch request first checks the cache, returns cached data if available, or fetches from network and caches the response.

Execution Sample

NextJS

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

Fetches data from an API using Next.js fetch with cache set to 'force-cache' to reuse cached response if available.

Execution Table

Step	Action	Cache Status	Network Request	Result
1	Start fetch for URL	Check cache	No	Waiting
2	Cache hit found	Hit	No	Return cached response
3	Parse cached response	Hit	No	Data ready
4	Output data	Hit	No	Data logged
5	Start fetch for URL	Check cache	No	Waiting
6	Cache miss found	Miss	Yes	Send network request
7	Receive network response	Miss	Yes	Response received
8	Store response in cache	Miss	Yes	Cache updated
9	Parse response	Miss	No	Data ready
10	Output data	Miss	No	Data logged

💡 Execution stops after data is logged from either cached or network response.

Variable Tracker

Variable	Start	After Step 2	After Step 7	After Step 8	Final
cacheStatus	undefined	Hit	Miss	Miss	Miss
networkRequestSent	false	false	true	true	true
responseData	undefined	cached data	undefined	network data	network data

Key Moments - 3 Insights

Why does fetch sometimes not make a network request?

Because the cache has a valid response (cache hit), fetch returns cached data without network request, as shown in execution_table rows 2-4.

What happens when the cache does not have the requested data?

Fetch makes a network request to get fresh data, then stores it in cache for future use, as shown in execution_table rows 6-9.

Does fetch always update the cache after a network request?

Yes, after a cache miss and network fetch, the response is stored in cache for next time, shown in execution_table row 8.

Visual Quiz - 3 Questions

Look at the execution table, at which step is the network request sent when cache misses?

A Step 2

B Step 4

C Step 6

D Step 9

💡 Hint

Check the 'Network Request' column for 'Yes' when cache status is 'Miss'.

According to variable_tracker, what is the value of 'cacheStatus' after step 2?

A Hit

B Miss

C undefined

D false

💡 Hint

Look at the 'cacheStatus' row under 'After Step 2' column.

If the cache always misses, how would the 'networkRequestSent' variable change in the table?

A It would be 'false' for all steps

B It would be 'true' at every fetch attempt step

C It would be 'true' only at step 2

D It would be 'undefined'

💡 Hint

Consider that a cache miss triggers a network request each time.

Concept Snapshot

Fetch caching behavior in Next.js:
- fetch() checks cache first
- If cache hit, returns cached response
- If cache miss, makes network request
- Network response is stored in cache
- cache option controls this behavior (e.g., 'force-cache')

Full Transcript

This visual trace shows how Next.js fetch caching works. When fetch is called, it first checks if the requested URL response is in cache. If yes, it returns the cached data immediately without a network request. If no cached data is found, fetch makes a network request to get fresh data, then stores that response in cache for future use. Variables like cacheStatus and networkRequestSent track this process. This helps improve performance by reusing data when possible and only fetching new data when needed.

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