Next.js Static Site Generation (SSG) vs. Server-Side Rendering (SSR): A Technical Comparison

Next.js has revolutionized modern web development by offering multiple rendering strategies, with Static Site Generation (SSG) and Server-Side Rendering (SSR) being two of the most prominent. Understanding the differences between these approaches is crucial for optimizing performance, scalability, and user experience.

In this post, we'll explore SSG and SSR in Next.js, compare their use cases, and provide practical examples to help you choose the right approach for your project.

What is Static Site Generation (SSG)?

Static Site Generation (SSG) pre-renders pages at build time, generating HTML files that can be served directly from a CDN. This approach is ideal for content that doesn't change frequently, such as blogs, marketing pages, or documentation.

Advantages of SSG

• Blazing Fast Performance: Since pages are pre-built, they load instantly.
• Reduced Server Load: No server-side processing is required for each request.
• SEO-Friendly: Search engines can easily crawl static content.

Example: SSG in Next.js

To implement SSG in Next.js, you can use getStaticProps to fetch data at build time:

// pages/blog/[slug].js
export async function getStaticProps({ params }) {
  const post = await fetch(`https://api.example.com/posts/${params.slug}`).then(res => res.json());
  return {
    props: { post },
    revalidate: 60, // Optional: Incremental Static Regeneration (ISR)
  };
}

export async function getStaticPaths() {
  const posts = await fetch('https://api.example.com/posts').then(res => res.json());
  const paths = posts.map(post => ({
    params: { slug: post.slug },
  }));
  return { paths, fallback: 'blocking' };
}

Here, getStaticPaths defines dynamic routes, while getStaticProps fetches data for each route at build time.

What is Server-Side Rendering (SSR)?

Server-Side Rendering (SSR) generates HTML on the server for each request. This is useful for pages with dynamic content that changes frequently, such as dashboards or e-commerce product pages.

Advantages of SSR

• Real-Time Data: Content is always up-to-date since it's fetched on each request.
• Better for Personalization: Ideal for user-specific data.
• SEO Benefits: Like SSG, SSR ensures content is crawlable.

Example: SSR in Next.js

To use SSR, implement getServerSideProps:

// pages/dashboard.js
export async function getServerSideProps(context) {
  const { req } = context;
  const userData = await fetch(`https://api.example.com/user`, {
    headers: { Authorization: req.headers.authorization },
  }).then(res => res.json());

  return {
    props: { userData },
  };
}

This function runs on every request, fetching fresh data before rendering the page.

When to Use SSG vs. SSR

Use SSG When:

• Content is static or changes infrequently (e.g., blogs, documentation).
• Performance is a top priority.
• You want to leverage CDN caching.

Use SSR When:

• Content is highly dynamic (e.g., user dashboards, real-time analytics).
• You need access to request-time data (e.g., cookies, headers).
• SEO is critical, but data changes too often for SSG.

Hybrid Approaches

Next.js also supports hybrid rendering, combining SSG and SSR where needed:

1. Incremental Static Regeneration (ISR): Update static content after build time without redeploying.
2. Client-Side Fetching: Use useEffect or SWR for dynamic client-side updates.

Example: ISR with revalidate

// pages/products/[id].js
export async function getStaticProps({ params }) {
  const product = await fetch(`https://api.example.com/products/${params.id}`).then(res => res.json());
  return {
    props: { product },
    revalidate: 10, // Re-generate page every 10 seconds
  };
}

Conclusion

Choosing between SSG and SSR in Next.js depends on your project's requirements:

• SSG excels in performance and scalability for static content.
• SSR is better for dynamic, personalized experiences.

By leveraging hybrid approaches like ISR, you can get the best of both worlds. Evaluate your data needs, performance goals, and SEO requirements to make an informed decision.

For most projects, a combination of SSG for static pages and SSR for dynamic sections provides an optimal balance of speed and flexibility.