Demystifying Next.js: Server-Side Rendering vs…

Navigate the critical choice between Server-Side Rendering (SSR) and Static Site Generation (SSG) in Next.js. This deep dive explains when to use each for

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Shafat Mahmud Khan

July 9, 20268 min read

Demystifying Next.js: Server-Side Rendering vs…

As a developer working with Next.js, one of the most fundamental decisions you'll face is choosing the right data fetching strategy. It's not just about getting data; it's about performance, user experience, SEO, and scalability. Today, we're diving deep into the critical choice of server side rendering vs static site generation next.js. Understanding the nuances between these two powerful paradigms is key to building highly optimized web applications.

Next.js, with its hybrid rendering capabilities, offers incredible flexibility, allowing you to pick the best approach for each page or component. But with great power comes the need for clarity. Let's break down SSR and SSG, explore their strengths, weaknesses, and when to leverage each.

Understanding Server-Side Rendering (SSR) in Next.js

Server-Side Rendering in Next.js means that for every incoming request, the server fetches the necessary data and renders the complete HTML page on the fly. This fully rendered page is then sent to the client's browser. This process ensures that the user receives a complete page, ready for display, even before client-side JavaScript takes over.

How SSR Works

When a user navigates to an SSR page, Next.js calls the getServerSideProps function on the server. This function fetches data, which is then passed as props to your React component. The component renders into HTML, and that HTML, along with the necessary JavaScript, is sent to the browser.

Advantages of SSR

Up-to-Date Data: Ideal for highly dynamic content that changes frequently, like stock prices, real-time dashboards, or personalized user feeds. Every request gets the latest data.
Excellent SEO: Search engine crawlers receive a fully rendered HTML page, which makes indexing and ranking much easier compared to client-side rendered (CSR) applications.
Better Initial Load Performance: Users see content faster because the browser doesn't have to wait for JavaScript to download, execute, and fetch data before rendering.
Access to Request Context: getServerSideProps has access to the request object (headers, cookies, URL parameters), which is crucial for authentication, redirects, or A/B testing.

Disadvantages of SSR

Slower Time To First Byte (TTFB): Since the server has to fetch data and render the page for each request, the initial response can be slower compared to pre-built static pages.
Increased Server Load: Each request consumes server resources (CPU, memory). This can become a bottleneck for high-traffic sites without proper scaling.
Potential for Caching Issues: Caching strategies can be more complex due to the dynamic nature of content.

When to Use SSR

I typically recommend SSR for:

Pages displaying frequently changing data (e.g., e-commerce product pages with real-time stock).
User-specific dashboards or authenticated content.
Applications that absolutely require the freshest data on every page load.
Any page where SEO is paramount and content changes too often for static generation.

For projects dealing with complex data models for user-specific content, you might also be thinking about your database choices, as efficient data retrieval is key for good SSR performance.

SSR Code Example: `getServerSideProps`

Here's a simple example of fetching data on the server side using getServerSideProps:


// pages/posts/[id].js
import Head from 'next/head';

function Post({ post }) {
  if (!post) return <p>Loading...</p>; // Handle potential loading state or error

  return (
    <div>
      <Head>
        <title>{post.title}</title>
      </Head>
      <h1>{post.title}</h1>
      <p>{post.body}</p>
    </div>
  );
}

export async function getServerSideProps(context) {
  const { id } = context.params;
  // This function runs on the server for every request.
  const res = await fetch(`https://jsonplaceholder.typicode.com/posts/${id}`);
  const post = await res.json();

  if (!res.ok || !post.id) { // Check if the post exists
    return {
      notFound: true, // Redirects to 404 page if post not found
    };
  }

  return {
    props: {
      post,
    },
  };
}

export default Post;

Next.js Server-Side Rendering Static illustration — Working with Next.js Server-Side Rendering Static in real projects — practical implementation insights

Exploring Static Site Generation (SSG) in Next.js

Static Site Generation involves building your pages into static HTML, CSS, and JavaScript files at build time. This means the pages are pre-rendered once and then served directly from a CDN (Content Delivery Network) to every user, making them incredibly fast and resilient.

How SSG Works

During the build process (e.g., when you run next build), Next.js executes the getStaticProps function (and optionally getStaticPaths for dynamic routes) to fetch data. It then renders the component into an HTML file. This file is then deployed and served. When a user requests an SSG page, the CDN immediately delivers the pre-built HTML, offering near-instant loading times.

Advantages of SSG

Blazing Fast Performance: Pages are served directly from a CDN, resulting in extremely low TTFB and excellent user experience. There's no server-side computation at request time.
Enhanced Security: With no server-side logic executed on request, there's a smaller attack surface.
Lower Hosting Costs: Serving static files is significantly cheaper and scales more easily than running dynamic servers.
Excellent SEO: Like SSR, search engines get fully formed HTML, ensuring great indexability.
Simplified Caching: Static files are inherently easy to cache, often handled automatically by CDNs.

Disadvantages of SSG

Stale Data (without revalidation): Without mechanisms like Incremental Static Regeneration (ISR), content is only updated when you rebuild and redeploy the site.
Not Suitable for Highly Dynamic Content: If content changes every second or is unique to each user, SSG alone might not be the best fit.
Build Time: For very large sites with thousands of pages, the build process can take a long time.

When to Use SSG

SSG shines in scenarios like:

Blogs and documentation sites.
Marketing pages, landing pages, and portfolios.
E-commerce product listings where inventory doesn't change by the second.
Any content that doesn't need to be updated in real-time for every single user request.

When building components for these static pages, especially if they involve complex user interactions, it's worth reviewing best practices for state management in React TypeScript to ensure a smooth client-side experience.

SSG Code Example: `getStaticProps`

Here's how you might fetch data at build time for a blog post:


// pages/blog/[slug].js
import Head from 'next/head';

function BlogPost({ post }) {
  return (
    <div>
      <Head>
        <title>{post.title}</title>
      </Head>
      <h1>{post.title}</h1>
      <p>{post.content}</p>
    </div>
  );
}

export async function getStaticPaths() {
  // Fetch a list of all possible slugs
  const res = await fetch('https://api.example.com/posts');
  const posts = await res.json();

  const paths = posts.map((post) => ({
    params: { slug: post.slug },
  }));

  return { paths, fallback: 'blocking' }; // 'blocking' shows loading state then fetches
}

export async function getStaticProps({ params }) {
  // Fetch individual post data based on slug
  const res = await fetch(`https://api.example.com/posts/${params.slug}`);
  const post = await res.json();

  if (!post) { // Check if the post exists
    return {
      notFound: true,
    };
  }

  return {
    props: {
      post,
    },
    revalidate: 60, // Incremental Static Regeneration: re-fetch data every 60 seconds
  };
}

export default BlogPost;

Server Side Rendering vs Static Site Generation Next.js: Making the Choice

So, how do you decide between SSR and SSG for your Next.js project? It often comes down to the nature of your content and your performance priorities. Here's a quick decision guide:

Content Volatility:
- SSR: Content changes very frequently, requires real-time updates for every user.
- SSG: Content is relatively static or can tolerate slight delays (e.g., a few minutes) via ISR.
User Personalization:
- SSR: Highly personalized content (e.g., user dashboards, authenticated pages) benefits from server-side logic per request.
- SSG: Less personalized, or personalization happens client-side after initial static load.
Build Time vs. Request Time:
- SSR: Computation happens on every request, potentially slower TTFB but always fresh.
- SSG: Computation happens at build time, leading to super-fast TTFB but content only as fresh as the last build/revalidation.
Scalability & Cost:
- SSR: Requires more robust server infrastructure to scale, potentially higher costs.
- SSG: Highly scalable with CDNs, lower hosting costs.
SEO Needs: Both offer excellent SEO for indexed content as they provide fully rendered HTML. The key differentiator is content freshness.

Remember, Next.js allows you to use both strategies within the same application. You can have an SSG blog and an SSR authenticated dashboard coexisting beautifully. This hybrid approach is one of Next.js's greatest strengths.

FAQ

What is Incremental Static Regeneration (ISR)?

ISR is a powerful Next.js feature that allows you to update static pages after they've been built, without needing to rebuild the entire site. By adding a revalidate property to getStaticProps, you tell Next.js to regenerate the page in the background after a certain period, serving the old (stale) page for a bit until the new one is ready. This combines the performance benefits of SSG with the freshness of SSR, addressing one of the core limitations in the server side rendering vs static site generation Next.js discussion.

Can I combine SSR and SSG in a single Next.js application?

Absolutely, and this is one of Next.js's most compelling features! You can use getStaticProps for your blog posts and marketing pages, and getServerSideProps for your user dashboards or any page requiring real-time, user-specific data. This hybrid approach allows you to optimize each part of your application for its specific needs, leveraging the best of both worlds.

When should I avoid using SSR or SSG and opt for Client-Side Rendering (CSR) instead?

While SSR and SSG offer significant SEO and performance benefits, there are cases where pure CSR (fetching data client-side after initial render) is suitable. For instance, highly interactive dashboards where the initial data is less important than the subsequent client-side updates, or internal tools where SEO is not a concern. Next.js still supports CSR by default for components that don't use getStaticProps or getServerSideProps. You might also consider CSR when dealing with sensitive, non-cacheable user data that shouldn't be exposed during build or server-side rendering, though SSR can handle this securely with proper authentication and headers.

Conclusion: Mastering Your Next.js Rendering Strategy

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Demystifying Next.js: Server-Side Rendering vs…