Incremental Static Regeneration (ISR): the best of both worlds

Incremental Static Regeneration (ISR) combines the lightning fast performance of Static Site Generation with the dynamic capabilities of Server Side Rendering. This powerful feature allows you to update static content without rebuilding your entire site.

In this guide, we'll explore what ISR is, how it works, and when to use it in your projects.

🔍 What is ISR?

ISR is a hybrid rendering technique that updates static content in the background. It generates static pages at build time, then regenerates them when needed without rebuilding the entire site.

How ISR works

1. Build Time: Generate popular pages statically
2. Request Time: Serve cached version instantly
3. Background: Regenerate stale content automatically
4. Update: Replace cache with fresh content

// Next.js ISR example
export async function getStaticProps() {
  const data = await fetchData();

  return {
    props: { data },
    revalidate: 60 // Revalidate every 60 seconds
  };
}

🚀 ISR Vs other methods

🎯 When to use ISR

Don't use ISR for:

• Real time data (chat, live feeds)
• Highly personalized content
• Content that never changes

⚙️ ISR Configuration

Revalidation times

Implementation example

export async function getStaticProps({ params }) {
  try {
    const data = await fetchData(params.id);

    return {
      props: { data },
      revalidate: 300 // 5 minutes
    };
  } catch (error) {
    return {
      notFound: true,
      revalidate: 60 // Retry sooner on errors
    };
  }
}

export async function getStaticPaths() {
  const popularPages = await getPopularPages();

  return {
    paths: popularPages.map(page => ({ params: { id: page.id } })),
    fallback: 'blocking' // Generate others on-demand
  };
}

🔧 Best practices

Smart pre-generation

Only pre-build your most important pages:

// Focus on top 100 most popular posts
const popularPosts = await getTopPosts(100);

Error handling

Always handle failures gracefully:

try {
  const data = await fetchData();
  return { props: { data }, revalidate: 300 };
} catch (error) {
  return { notFound: true, revalidate: 60 };
}

Manual revalidation

Force updates for critical content:

// API route: /api/revalidate
export default async function handler(req, res) {
  await res.revalidate('/important-page');
  return res.json({ revalidated: true });
}

⚠️ ISR Limitations

• Users might see stale content briefly
• Currently limited to specific frameworks (Next.js, Nuxt.js)
• Requires understanding of cache behavior
• Background processing uses server resources

✅ Quick decision guide

Choose ISR when:

• Content updates regularly (but not constantly)
• Performance is critical
• You need SEO optimization
• Hosting costs matter

Skip ISR when:

• You need real time data
• Content never changes
• You need complex personalization

🧠 Conclusion

ISR solves the performance vs freshness dilemma by serving fast static content while updating it in the background. It's perfect for content driven sites that need both speed and up to date information.

With proper implementation, ISR delivers the best user experience: instant loading with fresh content, making it an excellent choice for modern web applications.