Boost Your Site's Speed: Next.js Rendering Explained

Boost Your Site's Speed: Next.js Rendering Explained

Boost Your Site's Speed: Next.js Rendering Explained

May 26, 2025

In today's fast-paced web world, users expect websites to load instantly. For developers using Next.js, a powerful React tool, making pages load faster is a big deal. Next.js offers way more than just basic server-side rendering, letting you fine-tune your app for top performance.

When you're building a huge website with thousands of pages, balancing how fast pages load with how much work your server has to do is super important. Picking the right rendering techniques is key to building a fast website that doesn't waste resources or cost you extra money. This blog will dive into the various Next.js rendering strategies, offering insights and practical code examples to help you build highly performant and cost-effective web applications.

How Next.js Pre-renders Your Pages

By default, Next.js pre-renders every page. This means it creates the basic HTML of your page before it gets to the user's browser. This is different from older methods where the browser had to build the page from scratch. Pre-rendering makes your site load faster initially and is better for SEO.

Next.js gives you powerful options to control this pre-rendering. Besides regular Client-Side Rendering (CSR), which happens entirely in the user's browser, Next.js offers two main pre-rendering types:

  • Server-Side Rendering (SSR): Pages are built on the server every time a user asks for them. This can add work to your server but is crucial for pages that need to show the latest information all the time or that need to look good when shared on social media (like Twitter or Facebook).

  • Static Site Generation (SSG): Pages are built once, when you build your website. The HTML, CSS, and JavaScript are all ready. Next.js even has smart ways to figure out if a page can be built this way, even if it uses some data.

When should you pre-render?

Pre-rendering is great for pages that need to be found easily by search engines (SEO) and look good when shared on social media. Imagine a user's profile page on a social site – it needs unique info for each user, so pre-rendering helps it show up correctly everywhere.

Beyond SEO, server-rendering HTML can really help with First Input Delay (FID). This measures how long it takes for a page to respond when a user first clicks or taps something. If your page loads a lot of data on the user's side, FID can feel slow, especially for people with slower internet.

Just be careful not to make your HTML too big when rendering on the server. If some content, like a list at the bottom of the page, isn't seen right away, it might be better to load that part on the client's side (CSR).

Deeper Dives: Smart Pre-rendering Methods

Next.js offers even more detailed ways to pre-render. The best choice depends on how much your page's content changes (variability), how many pages there are (bulk size), and how often content is updated or requested. Making the right choice helps keep your server happy and your hosting costs low.

Just like regular server-side rendering puts a lot of work on the server during use, pure static generation puts a lot of work on it during the build process. You need to pick the right method for each page based on:

  • Variability: How often does the page content change?

    • Time-dependent: Changes very often (e.g., every minute).

    • Action-dependent: Changes when a user does something (e.g., updates a profile).

    • Stale: Doesn't change unless you rebuild the whole site.

  • Bulk Size: How many pages are in this section (e.g., 30 movie genres or millions of products)?

  • Update Frequency: How often does the content change (e.g., 10 times a month)?

  • Request Frequency: How often do users ask for this page (e.g., 100 times a day)?

Let's look at some specific strategies.

Small Pages, Regular Updates: Incremental Static Regeneration (ISR)

Incremental Static Regeneration (ISR) is perfect for pages that are mostly static but need to update their info regularly. Next.js rebuilds these pages only when a new request comes in and the old version is past its refresh time.

For example, on a streaming app, a genre page (like "Action Movies") might need new content daily. If you only have about 200 genres, ISR is a great fit.

Here's how ISR looks in code:

JavaScript

// pages/genres/[id].js
export async function getStaticProps() {
  const posts = await fetch('url-endpoint').then((data) => data.json());
  
  /* revalidate at most every 10 secs */
  return { props: { posts }, revalidate: 10, }
}
export async function getStaticPaths() {
  const posts = await fetch('url-endpoint').then((data) => data.json());
  const paths = posts.map((post) => ({
    params: { id: post.id.toString() },
  }));
  return { paths, fallback: false } // If a path isn't here, it's a 404
}

This code tells Next.js to revalidate these pages at most every 10 seconds. It doesn't rebuild every 10 seconds, but only when someone asks for the page after that time.

Here's the process:

  1. User asks for an ISR page.

  2. Next.js sends the old (cached) page if it has one.

  3. In the background, Next.js checks if the page is older than 10 seconds.

  4. If it is, Next.js rebuilds the page. Next time someone asks for it, they get the new one.

Many Pages, Regular Updates: SSR with Caching or ISR with Fallback

Most big websites fall into this category. These are "public" pages where the content isn't specific to one user and doesn't need to be perfectly real-time. Since there might be millions of these pages (like product pages), building them all at once isn't an option.

SSR and Caching: Often the Best Pick

The best way here is usually Server-Side Rendering (SSR). The page is built when a user asks for it, then cached for a set time (e.g., an hour). Any later requests within that time get the cached page, saving your server from rebuilding it over and over.

Here’s a basic SSR and caching example:

JavaScript

// pages/products/[id].js
export async function getServerSideProps({ req, res }) {
  /* setting a cache of 10 secs for CDN */
  res.setHeader( 'Cache-Control', 'public, s-maxage=10, stale-while-revalidate=59')
  const data = await fetch('url-endpoint').then((res) => res.json());
  return {
    props: { data },
  }
}

You can learn more about caching headers in the Next.js caching documentation.

ISR and Fallback: When You Need Build Folder Access

Sometimes, even with millions of pages, you need them in the build folder for other reasons. In this case, you can skip building them at first and let Next.js build them on demand for the first request (or when the cached page gets old).

You'd add { fallback: 'blocking' } to getStaticPaths. During the build, you can prevent API calls so that no paths are generated. This skips the huge build time. Pages are then built as users ask for them and saved in your _next/static folder for future use.

Here's how to skip initial build generation:

JavaScript

// pages/products/[id].js (using fallback: 'blocking' for ISR)
export async function getStaticPaths() {
  if (process.env.SKIP_BUILD_STATIC_GENERATION === 'true') {
    return { paths: [], fallback: 'blocking' }; // Don't build paths now
  }
  return { paths: [], fallback: 'blocking' };
}

Then, you'd use revalidate in getStaticProps just like in the simple ISR example:

JavaScript

// pages/products/[id].js (getStaticProps with revalidate)
export async function getStaticProps({ params }) {
  const data = await fetch(`url-endpoint/${params.id}`).then((res) => res.json());
  return { props: { data }, revalidate: 10, } // Revalidate every 10 secs
}

Important: For lots of pages with regular updates, SSR with caching is usually better. The main downside of ISR with fallback: 'blocking' is that the very first user to visit a page might see a small delay while it's being built. Also, one user might see slightly old data from the cache, while another user (who triggers the refresh) sees the brand new data.

Content-dependent Updates: On-demand Revalidation (ODR)

On-demand Revalidation (ODR) lets you refresh a page instantly using a webhook or API call. This is super handy when your page content needs to be super accurate right away.

For example, if you have a blog with a system that tells you when content is updated, you can set it up to call a special API in your Next.js app. This API will then tell Next.js to rebuild only the affected blog page.

Here's an ODR example for an API route:

JavaScript

// pages/api/revalidate.js
export default async function handler(req, res) {
  // Check for a secret token for security
  if (req.query.secret !== process.env.MY_SECRET_TOKEN) {
    return res.status(401).json({ message: 'Invalid token' })
  }
  try {
    // Revalidate the specific page path (e.g., /blog/my-article-slug)
    await res.revalidate('/' + req.query.revalidate_path)
    return res.json({ revalidated: true })
  } catch (err) {
    return res.status(500).send('Error revalidating')
  }
}

If you have a huge number of pages (like 2 million), you might still skip building them initially by returning an empty array for paths in getStaticPaths:

JavaScript

// pages/blog/[slug].js (for dynamic blog posts with ODR)
export async function getStaticPaths() {
  return { paths: [], fallback: 'blocking' }; // Don't build now, build on demand
}
export async function getStaticProps({ params }) {
  const post = await fetch(`url-endpoint/${params.slug}`).then((res) => res.json());
  if (!post) {
    return { notFound: true };
  }
  return { props: { post }, revalidate: 3600 }; // Revalidate often as a backup
}

This avoids the "stale data" issue of ISR. Instead, both users see accurate data after a webhook triggers the refresh, which happens in the background.

Sometimes, even with content-dependent changes, if your pages are too many or update/get requested too often, you might switch to a time-dependent strategy (like ISR). Think of an IMDb movie page: reviews change, but you don't need to update the page every second. Shifting to ISR here can significantly lower server load.

With React Server Components and the App Router in Next.js 13, data fetching has improved, allowing Next.js to start rendering pages even before all data is ready.

Next.js Hybrid Approaches with Client-Side Rendering (CSR)

In Next.js, Client-Side Rendering (CSR) always happens after pre-rendering. It's often used as an add-on, especially to reduce server load or when parts of a page can be loaded later. Combining pre-rendering with CSR can be very beneficial.

If content is dynamic and doesn't need to be optimized for social media shares or search engines, CSR is a good choice. For example, you can pre-render an empty page layout (SSG/SSR) and then load the actual content later using CSR.

Consider a social media feed that updates every minute. The page title and basic info might stay the same (pre-rendered), while the changing feed content is loaded using CSR.

Dynamic Components: Load What You Need, When You Need It

CSR is great for content not seen when the page first loads, or for hidden parts like login pop-ups or alerts. You can show these by either loading their content after the main page renders or by lazy loading the component itself using next/dynamic.

Typically, a website loads HTML, then goes through hydration (where React makes parts interactive), and then uses CSR techniques like fetching data or loading dynamic components. Hydration can sometimes make a page feel slower, like an empty profile page slowly filling with content. If the content is ready when the page is pre-rendered, it's often better to pre-render it fully.

The suspense phase is the waiting time while a dynamic component loads. Next.js lets you show a temporary placeholder or "fallback" during this time.

Rendering Dynamic Components:

Here's how to load a component only on the client side:

JavaScript

// components/DynamicModal.js
import dynamic from 'next/dynamic'
/* loads the component on client side only */
const DynamicModal = dynamic(() => import('../components/modal'), {
  ssr: false, // Don't render this on the server
});
export default DynamicModal;

You can show a loading message while the component loads:

JavaScript

// pages/index.js
import dynamic from 'next/dynamic';
import { Suspense } from 'react';
/* enables Suspense fallback for the dynamic component */
const DynamicModal = dynamic(() => import('../components/modal'), {
  suspense: true, // Use Suspense
});
export default function Home() {
  return (
    <div>
      <h1>Welcome to My App</h1>
      {/* Shows "Loading Modal..." until DynamicModal is ready */}
      <Suspense fallback={<div>Loading Modal...</div>}>
        <DynamicModal />
      </Suspense>
      <p>This content is always visible.</p>
    </div>
  );
}

This way, the DynamicModal's code isn't part of the initial page load, making it faster. The "Loading..." message shows first, then the actual modal appears.

Next.js Caching: Smart Storage for Faster Loads

If you want faster pages and less server load, caching is your best friend. In SSR, we saw how caching can make high-traffic pages much faster. Next.js assets (pages, scripts, images) already have cache settings you can adjust.

When a user visits a website, the request goes through three checkpoints:

  1. Browser Cache: First stop. If the content is saved here and is fresh, it loads super fast.

  2. CDN Cache: Second stop. This is a network of servers around the world that store copies of your content, bringing it closer to users ("caching on the edge").

  3. Origin Server: Last stop. If the content isn't in the caches or is old, the request goes to your main server to get a fresh copy.

Next.js automatically adds caching headers for static assets like CSS and JavaScript from _next/static:

Cache-Control: public, max-age=31536000, immutable

For Server-Side Rendering (SSR), you set the cache header in getServerSideProps:

JavaScript

res.setHeader('Cache-Control', 'public, s-maxage=10, stale-while-revalidate=59');

For Static Site Generated (SSG) pages, the cache header is automatically created based on the revalidate option in getStaticProps.

Understanding and Configuring Cache Headers

Let's break down what each part of a cache header means:

  • public vs. private:

    • public: Anyone (like a CDN) can store this response. Use for content that's the same for all users.

    • private: Only the user's browser can store this. Use for private or user-specific info. Example: Cache-Control: private, s-maxage=1800 (for a private page).

  • s-maxage (Shared Cache Max Age): This sets how long a page can be considered "fresh" in a shared cache (like a CDN). If a request comes in after this time, the cache tries to get a fresh copy. Choose a value based on how often your content changes.

  • must-revalidate vs. stale-while-revalidate:

    • must-revalidate: Once the page is old, it must be refreshed from the server before being shown again. Use when old data is totally wrong (e.g., stock prices).

    • stale-while-revalidate: This is powerful! It lets the cached page be shown even if it's old, while the cache gets a fresh version in the background. The user sees the old version instantly, then the new one replaces it for the next request. This makes the page feel faster. Good for content that changes often but being slightly outdated for a moment is fine (e.g., a "trending" list). Example: Cache-Control: public, s-maxage=3600, stale-while-revalidate=59 (serve old for up to 59 seconds while refreshing).

  • stale-if-error: If the server fails to refresh the page, this sets how long the old (stale) data can still be used. It's a safety net. Example: Cache-Control: public, s-maxage=3600, stale-while-revalidate=59, stale-if-error=300 (serve old for up to 300 seconds if refresh fails).

Superflex.ai: Your Figma Designs, Live in Seconds!

By mastering these rendering and caching strategies, you can build Next.js apps that are not only fast and efficient but also scalable and cost-effective, giving your users a great experience.

While Next.js provides incredible tools for optimizing page speed once your code is written, the initial leap from a design in Figma to a functional website can still be a huge time sink. This is where Superflex.ai completely changes the game, bridging that gap with intelligent AI that transforms your Figma designs into clean, production-ready code in seconds.

Ready to revolutionize your workflow and launch your designs faster than ever before? Discover the power of Superflex.ai and bring your Figma visions to life today!

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