Dive into Next.js Server-Side Rendering (SSR): From SPA to ISR

Server-side rendering (SSR) and server components are not just buzzwords in modern web development—they’re key tools that can improve both SEO and user experience while making your app more efficient. In this first part of our series, we’ll explore how to properly set up SSR and dive into how server components can boost performance and simplify your app's architecture. We’ll break down the details to help you get the most out of these technologies and build an application that is fast, reliable, and user-friendly.

Performance Optimization: Speeding Things Up and Keeping Users Happy

Performance optimization isn't just a trendy phrase developers toss around—it’s critical for creating an exceptional user experience. A fast website is like a high-performance sports car: it’s not only impressive, but it also keeps users engaged and coming back for more.

When pages load instantly, and the interface feels smooth, users stick around. They’re less likely to close the tab out of frustration. A slow website? That’s like watching paint dry—no one wants to do that. The longer they wait, the more likely they are to leave and never return. This not only hurts user engagement but also your SEO, since search engines tend to favor faster sites.

But the benefits don’t stop there! Optimizing performance also reduces the load on your servers and cuts down on bandwidth consumption. This is particularly important for users with slower internet connections or older devices—they won't have to suffer through endless loading screens. Ultimately, performance optimization makes your site more accessible and enjoyable for everyone.

SSR: How Server-Side Rendering Changes the Game

When it comes to web application performance, understanding how rendering impacts the user experience is crucial. In the early days of React, most applications were built as single-page apps (SPA), relying heavily on client-side rendering. This approach had its merits, but it quickly became apparent that it wasn’t ideal for every scenario.

Enter Server-Side Rendering (SSR), the true game-changer for optimizing load times and interactivity. SSR allows pages to be rendered on the server and delivered to the user already fully composed, completely shifting the user experience.

But SSR is just one part of a bigger picture. As it evolved, new concepts emerged, like Static Site Generation (SSG) and Incremental Static Regeneration (ISR). These approaches open even more doors for optimization, making your applications faster and more responsive.

In the next section, we'll dive into the specifics of SSR, explore how it revolutionized React application development, and examine its benefits. Then, we’ll move on to server components and their role in this fascinating process.

The Evolution of React Applications: From SPA to SSR

When we first started using React, most applications were single-page apps (SPAs) relying on client-side rendering. The process looked straightforward: we had a single HTML file with a root div and a script that loaded our bundle:

<html>
  <head>
    <!-- Styles, meta tags, external scripts, etc. -->
  </head>
  <body>
    <div id="root"></div>
    <script src="/dir/bundle.js"></script>
  </body>
</html>

Once the bundle was loaded, React took over, rendering the DOM for the application and inserting it into the div. However, until this process was complete, users would see nothing but a blank screen, delaying the First Contentful Paint (FCP) — the moment the first visible element appeared on the screen.

But this was just the beginning of the wait. Even after the interface was displayed, the app still had to become interactive. This process took additional time, and only after React added event handling did Time to Interactive (TTI) occur.

As apps grew in size, these delays worsened. But even that wasn’t the end of the waiting.

Finally, users often encountered loaders or skeletons while waiting for data to arrive from an API. The Largest Contentful Paint (LCP) — the moment when the actual content replaced the skeletons — signaled the end of this loading process.

Enter Server-Side Rendering (SSR)! With SSR, the page is rendered on the server and sent to the user fully assembled. The bundle script is still necessary, but this approach offers two significant advantages:

A fully-rendered page for the user: Instead of seeing a blank screen as they would with client-side rendering, users receive a fully rendered page with content right away, dramatically speeding up FCP.
Client-side hydration: React no longer creates the entire DOM from scratch; instead, it works with the existing content, adding interactivity through a process called hydration. This reduces the TTI because the browser only needs to add dynamic elements, rather than build the entire interface from scratch.

Moreover, SSR sped up the display of final content. Unlike client-side rendering, where LCP could be delayed until data was fetched from an API, server-side rendering allowed for ready-to-display content. This not only sped up the loading process but also made the entire interaction smoother and more responsive for the user.

By leveraging SSR, we were able to make React applications faster and more enjoyable for users, leading to better user retention and an improved overall experience.

The Evolution of SSR: SSG and ISR

Server-Side Rendering was just the beginning, but over the years, new methods have emerged to make static site generation even more powerful and flexible. Let’s explore Static Site Generation (SSG) and Incremental Static Regeneration (ISR) — two techniques that have pushed performance to the next level.

1. Static Site Generation (SSG) — Build-Time Rendering

Imagine this: instead of generating pages on every request (as SSR does), pages are generated once — at build time. This is Static Site Generation. The user gets a pre-built HTML page almost instantly because it's already prepared, significantly reducing server load and speeding up the page load.

The beauty of it? Even though the page is static, it retains all the interactivity thanks to React’s hydration — when JavaScript "brings to life" the pre-rendered page and adds dynamic behavior.

In Next.js, if you’re not using getServerSideProps or getInitialProps, pages are generated using SSG by default. This makes your site incredibly fast by relying on static content.

2. Incremental Static Regeneration (ISR) — Dynamic Generation on Request

ISR takes SSG to the next level. What if your pages could update dynamically, but without rebuilding the entire site? That’s what ISR does. You can update pre-generated pages at specific intervals or even on demand, without wasting resources on regenerating everything.

Let’s say you have an e-commerce store with hundreds of products. Instead of rebuilding the entire catalog every time something changes, ISR allows you to regenerate only the pages that have been requested and have outdated cache. Here’s an example of using revalidate for a product page:

interface Props {
  product: Product;
}

export const getStaticProps: GetStaticProps<Props> = async ({ params }) => {
  const response = await fetch(`https://api.store.app/product/${params.id}`);
  const product = await response.json();

  return {
    props: { product },
    // Cache lifetime for the page in seconds
    // Next.js will automatically set cache-control headers
    revalidate: 600, 
  };
};

Now, the product pages stay cached for the specified duration. But if someone requests a page after that time (in our example, 10 minutes), Next.js will regenerate the page. After that, the new version will remain in the cache for the next set period. Additionally, if a new product is added, Next.js will generate the page "on-the-fly" during the first request and cache it for the same duration.

SSR and Its Optimization Horizons

SSR became a great solution for improving load times and initial rendering in React, while evolutionary methods like Static Site Generation (SSG) and Incremental Static Regeneration (ISR) have given us more control and flexibility in building optimal, fast, and scalable applications.

With these methods, we can now offer users pre-built pages with minimal delay, dynamically update them when necessary, and most importantly, reduce server load.

But the evolution doesn’t stop here. In the React world, another powerful tool is emerging — server components. These components take server-side rendering to a new level, changing how we divide logic between client and server. In the next part, we’ll dive into how server components work and why they’re crucial for further optimizing performance.

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