Cache invalidation strategies in NextJS

Introduction

Cache invalidation strategies help keep your app's data fresh by deciding when to update or remove stored data. This avoids showing old information to users.

When you fetch data that changes often, like user profiles or news feeds.

When you want to improve app speed but still show up-to-date content.

When you use Next.js data fetching methods like <code>getStaticProps</code> or <code>getServerSideProps</code>.

When you cache API responses or images and need to refresh them after updates.

When you want to balance between fast loading and accurate data.

Syntax

NextJS

export async function getStaticProps() {
  const data = await fetchData()
  return {
    props: { data },
    revalidate: 60 // seconds
  }
}

The revalidate key tells Next.js to update the cached page after the given seconds.

This is called Incremental Static Regeneration (ISR) in Next.js.

Examples

This example fetches posts and refreshes the cache every 10 seconds.

NextJS

export async function getStaticProps() {
  const data = await fetch('https://api.example.com/posts').then(res => res.json())
  return {
    props: { posts: data },
    revalidate: 10 // update cache every 10 seconds
  }
}

This fetches fresh data on every request, so no caching is needed.

NextJS

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

This generates a static page at build time. It stays the same until you redeploy the app. No automatic cache regeneration.

NextJS

export async function getStaticProps() {
  const data = await fetchData()
  return {
    props: { data }
  }
}

Sample Program

This Next.js page fetches a post and caches it. The cache updates every 30 seconds, so users see fresh content without slowing down the page.

NextJS

import React from 'react'

export async function getStaticProps() {
  const res = await fetch('https://jsonplaceholder.typicode.com/posts/1')
  const post = await res.json()
  return {
    props: { post },
    revalidate: 30 // refresh cache every 30 seconds
  }
}

export default function Post({ post }) {
  return (
    <main>
      <h1>{post.title}</h1>
      <p>{post.body}</p>
    </main>
  )
}

Important Notes

Use revalidate in getStaticProps for automatic cache updates.

getServerSideProps always fetches fresh data on each request, so no caching is done.

Choose cache times based on how often your data changes and how fresh it needs to be.

Summary

Cache invalidation keeps your app data fresh and fast.

Next.js uses revalidate in getStaticProps for incremental updates.

Use getServerSideProps for always fresh data without caching.

Practice

1. In Next.js, which method allows you to update static pages after a certain time interval to keep data fresh without rebuilding the entire site?

easy

A. getServerSideProps without caching

B. Manually clearing browser cache

C. Using client-side useEffect to fetch data

D. getStaticProps with revalidate

Solution

1. Step 1: Understand Next.js data fetching methods

   getStaticProps generates static pages at build time, but with revalidate, it can update pages after a set interval.

2. Step 2: Compare with other methods

   getServerSideProps fetches fresh data on every request but does not use caching or revalidation intervals.

3. Final Answer:

   getStaticProps with revalidate -> Option D

4. Quick Check:

   Incremental Static Regeneration = getStaticProps + revalidate [OK]

Hint: Remember: revalidate updates static pages periodically [OK]

Common Mistakes:

• Confusing getServerSideProps with revalidation
• Thinking client-side fetching is cache invalidation
• Assuming manual browser cache clearing affects server cache

2. Which of the following is the correct way to set a revalidation time of 10 seconds in getStaticProps?

easy

A. return { props: {}, revalidate: 10 }

B. return { props: {}, revalidateTime: 10 }

C. return { props: {}, cache: 10 }

D. return { props: {}, refresh: 10 }

Solution

1. Step 1: Recall the correct property name for revalidation

   The Next.js documentation specifies revalidate as the property to set seconds for incremental static regeneration.

2. Step 2: Check the return object structure

   The return object from getStaticProps must include props and optionally revalidate with a number value.

3. Final Answer:

   return { props: {}, revalidate: 10 } -> Option A

4. Quick Check:

   Property name is revalidate [OK]

Hint: Use exact property name 'revalidate' in return object [OK]

Common Mistakes:

• Using incorrect property names like 'revalidateTime' or 'refresh'
• Placing revalidate outside the return object
• Setting revalidate as a string instead of a number

3. Consider this Next.js code snippet:

export async function getStaticProps() {
  return {
    props: { time: Date.now() },
    revalidate: 5
  };
}

What will happen if you visit this page multiple times within 5 seconds?

medium

A. The page will throw an error due to Date.now() in getStaticProps

B. The page will show the same timestamp for all visits within 5 seconds

C. The page will update the timestamp on every visit

D. The page will never update the timestamp

Solution

1. Step 1: Understand revalidate behavior

   The revalidate: 5 means Next.js will regenerate the page at most every 5 seconds.

2. Step 2: Predict output within 5 seconds

   Within 5 seconds, the cached page is served, so the timestamp remains the same for all visits.

3. Final Answer:

   The page will show the same timestamp for all visits within 5 seconds -> Option B

4. Quick Check:

   Revalidate interval caches page for 5 seconds [OK]

Hint: Revalidate caches page until interval expires [OK]

Common Mistakes:

• Assuming timestamp updates on every visit
• Thinking Date.now() causes errors in static props
• Believing revalidate disables caching

4. You wrote this code in Next.js:

export async function getStaticProps() {
  return {
    props: { data: await fetchData() },
    revalidate: '10'
  };
}

Why does this cause a problem?

medium

A. Because revalidate must be a number, not a string

B. Because fetchData cannot be awaited in getStaticProps

C. Because props must be a function, not an object

D. Because revalidate cannot be used with getStaticProps

Solution

1. Step 1: Check the type of revalidate

   The revalidate property expects a number representing seconds, not a string.

2. Step 2: Understand impact of wrong type

   Passing a string causes Next.js to throw a type error or ignore the revalidation, breaking cache invalidation.

3. Final Answer:

   revalidate must be a number, not a string -> Option A

4. Quick Check:

   Revalidate value type = number [OK]

Hint: Use number type for revalidate seconds [OK]

Common Mistakes:

• Passing revalidate as a string
• Thinking async/await is disallowed in getStaticProps
• Confusing props structure requirements

5. You want to always serve fresh data on every request in Next.js without caching. Which method should you use and why?

hard

A. Use getStaticProps without revalidate

B. Use getStaticProps with revalidate: 0

C. Use getServerSideProps because it runs on every request

D. Use client-side fetching only with useEffect

Solution

1. Step 1: Identify method for fresh data every request

   getServerSideProps runs on the server for every page request, ensuring fresh data.

2. Step 2: Compare with static methods

   getStaticProps generates static pages at build time or with revalidation intervals, so it does not guarantee fresh data every request.

3. Final Answer:

   Use getServerSideProps because it runs on every request -> Option C

4. Quick Check:

   Fresh data every request = getServerSideProps [OK]

Hint: Always fresh data? Use getServerSideProps [OK]

Common Mistakes:

• Using revalidate: 0 expecting no caching
• Relying only on client-side fetching for SEO
• Confusing static and server-side methods