SSR vs ISR vs CSR in Next.js: Understanding the Key Rendering Strategies

When building web applications with Next.js, understanding its rendering strategies is crucial for optimizing performance and user experience. This blog will dive into Server-Side Rendering (SSR), Incremental Static Regeneration (ISR), and Client-Side Rendering (CSR), their use cases, and how to implement them.

What is SSR (Server-Side Rendering)?

Server-Side Rendering in Next.js involves generating the HTML for a page on the server for every request. This ensures that users always receive the latest data when they visit the page.

Key Features of SSR:

• Fresh data: HTML is generated dynamically for every request.
• SEO-friendly: Since the content is pre-rendered on the server, search engines can easily index it.
• Increased server load: Rendering on each request can increase server processing time.

How to Implement SSR in Next.js:

Use the getServerSideProps function to fetch data at request time:

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

  return {
    props: { data }, // Will be passed to the page component as props
  };
}

export default function Page({ data }) {
  return <div>{data.title}</div>;
}

What is ISR (Incremental Static Regeneration)?

Incremental Static Regeneration allows you to update static pages after the build process, without rebuilding the entire site. This is a powerful feature for pages that don’t require real-time updates but need occasional content refresh.

Key Features of ISR:

• Static performance with flexibility: Combines the speed of static pages with the ability to update content.
• Efficient caching: Pages are regenerated in the background while users see the cached version.
• Best for dynamic content: Ideal for blogs, e-commerce product pages, or any page updated at regular intervals.

How to Implement ISR in Next.js:
Use the getStaticProps function with the revalidate option:

export async function getStaticProps() {
  const res = await fetch('https://api.example.com/data');
  const data = await res.json();

  return {
    props: { data }, // Will be passed to the page component as props
    revalidate: 10, // Regenerate the page every 10 seconds
  };
}

export default function Page({ data }) {
  return <div>{data.title}</div>;
}

What is CSR (Client-Side Rendering)?

Client-Side Rendering relies on JavaScript to fetch and render content in the browser after the initial page load. This approach is common in single-page applications (SPAs).

Key Features of CSR:

• Dynamic interactions: Great for highly interactive applications.
• SEO challenges: Content is rendered after the initial load, which can make it harder for search engines to index.
• Fast initial load: Initial HTML is light, as it contains minimal content.

How to Implement CSR in Next.js:
Fetch data using React’s useEffect hook or a data-fetching library like SWR:

import { useEffect, useState } from 'react';

export default function Page() {
  const [data, setData] = useState(null);

  useEffect(() => {
    fetch('https://api.example.com/data')
      .then((res) => res.json())
      .then((data) => setData(data));
  }, []);

  if (!data) return <div>Loading...</div>;

  return <div>{data.title}</div>;
}

Comparison Table: SSR vs ISR vs CSR

Feature	SSR	ISR	CSR
Rendering	Server-side, per request	Static, with periodic updates	Client-side, in browser
Performance	Slower, depends on server	Fast, cached static pages	Fast initial load
SEO	Excellent	Excellent	Challenging
Use Cases	Real-time data, user-specific pages	Content-heavy sites, blogs	SPAs, interactive apps

When to Use Each Rendering Strategy?

Use SSR when:

• You need real-time data updates.
• SEO is a priority for frequently changing content.
• Pages are personalized for each user.

Use ISR when:

• Your data changes periodically.
• You want to serve static pages but keep them updated.
• Scalability and performance are important.

Use CSR when:

• Your app requires heavy interactivity.
• SEO is not a priority.
• You’re building SPAs with minimal server-side dependencies.

Conclusion

Next.js provides a versatile toolkit with SSR, ISR, and CSR, allowing developers to build tailored experiences. By understanding the strengths and weaknesses of each, you can choose the best strategy for your application’s needs. Whether it's a high-performance blog, a real-time dashboard, or an interactive SPA, Next.js has you covered.

Which rendering strategy do you use in your projects? Let us know in the comments!