Server-Side Rendering vs. Client-Side Rendering vs. Static Generation: When to Use What?

Published at: December 25, 2022

When building modern web applications, choosing the right rendering method is crucial for performance, SEO, and user experience. In Next.js, you have a variety of options to handle how your pages are rendered, such as Server-Side Rendering (SSR), Client-Side Rendering (CSR), Static Generation (SSG), and Incremental Static Regeneration (ISR). Each of these methods has its advantages and is suitable for different types of applications. In this blog post, we’ll compare these rendering techniques and help you choose the best approach for your Next.js project.

What Is Server-Side Rendering (SSR)?

Server-Side Rendering (SSR) refers to the process where the content of a web page is generated on the server each time a request is made. This means that the server will render the page’s HTML before sending it to the browser. In Next.js, SSR is implemented using the getServerSideProps function.

How SSR Works:

The user makes a request to the server.
The server runs your code, fetches data, and generates the HTML.
The server sends the fully rendered HTML to the client.
The client receives the HTML, and React takes over for interactivity (hydration).

When to Use SSR:

SSR is ideal for applications that require real-time data or need to ensure that the content is up-to-date every time the user accesses the page. Some use cases for SSR include:

Dynamic content: When the page content changes frequently or needs to reflect the most current data.
Personalized content: For displaying user-specific information based on authentication or session data.
SEO-friendly pages: Pages where SEO is a priority and the page content needs to be available to search engine crawlers immediately.

Pros of SSR:

SEO benefits: Search engines can crawl fully rendered HTML.
Data is always fresh because the page is generated on each request.
Great for applications with personalized or user-specific data.

Cons of SSR:

Slower initial load time due to server-side processing.
Higher server load since the server must render the page on every request.
Not ideal for pages that don’t require dynamic content or updates.

What Is Client-Side Rendering (CSR)?

Client-Side Rendering (CSR) refers to the traditional way of rendering pages where the browser is responsible for fetching the HTML, JavaScript, and other resources, and then rendering the page dynamically. The server simply serves the JavaScript, which runs in the browser to build the page. This is typically seen in single-page applications (SPAs).

How CSR Works:

The user requests a page.
The server sends a minimal HTML page and JavaScript files.
The browser loads the JavaScript, which fetches data (via API calls) and renders the page content.

When to Use CSR:

CSR is ideal when the page content doesn’t need to be indexed by search engines or doesn’t change frequently. Some use cases for CSR include:

Single-page applications (SPA): Apps that have smooth transitions and navigation without needing to reload the page.
Highly interactive UIs: Apps where the client-side JavaScript is responsible for dynamic updates based on user interactions.
Dashboard-like applications: When there’s frequent data fetching, and SEO is not a primary concern.

Pros of CSR:

Fast subsequent page loads after the initial load due to client-side navigation.
Good for highly interactive applications with complex UI states.
Less load on the server, as the page is rendered by the browser.

Cons of CSR:

Initial load time may be slower because the browser needs to download and execute JavaScript.
Not SEO-friendly out of the box, as search engine bots typically don’t execute JavaScript well.
The first render is slower, as the browser has to wait for JavaScript to load before rendering the content.

What Is Static Generation (SSG)?

Static Generation (SSG) is a method where the page content is pre-rendered at build time. With SSG, the HTML for each page is generated ahead of time and stored as static files, which can then be served by the server or a content delivery network (CDN). In Next.js, this is achieved using the getStaticProps function.

How SSG Works:

During the build process, Next.js fetches data and generates static HTML pages.
These static HTML files are stored and served directly to the user when requested.
React is used to add interactivity once the page is loaded in the browser.

When to Use SSG:

SSG is ideal for applications where the content does not change frequently or can be pre-rendered. Some use cases for SSG include:

Marketing websites: Where pages like landing pages, blogs, and product pages have content that doesn’t change frequently.
E-commerce pages: Product pages with static information that doesn’t need to change often.
Blog posts: Content that is pre-rendered at build time and doesn’t need real-time updates.

Pros of SSG:

Fast load times: Static pages are served quickly and can be cached by CDNs.
Best performance: Since the page is pre-generated, users receive it instantly.
SEO-friendly: Content is available to search engines immediately, as it’s pre-rendered.

Cons of SSG:

Content is static, meaning it can become outdated if not updated frequently.
Requires a build step whenever content changes, so the content can’t be updated in real-time unless the site is rebuilt.

What Is Incremental Static Regeneration (ISR)?

Incremental Static Regeneration (ISR) is a feature of Next.js that allows you to update static content after the build process without rebuilding the entire site. This means you can serve static pages while also allowing certain pages to be updated periodically.

How ISR Works:

Pages are pre-rendered at build time, just like Static Generation (SSG).
ISR allows you to update static pages on demand using a revalidation time (e.g., 10 seconds, 1 hour).
When a user requests a page that has been revalidated, Next.js regenerates the page in the background while serving the cached version to other users.

When to Use ISR:

ISR is perfect for websites that need to have static content but also need to periodically update the content without rebuilding the entire site. Some use cases for ISR include:

Content-heavy sites: Sites that display news articles, product lists, or blog posts that need to be updated regularly.
E-commerce sites: When product availability or prices change but the majority of the content can remain static.
Event-driven sites: Websites where content changes frequently but doesn’t require a full rebuild every time.

Pros of ISR:

Allows content to be updated at set intervals, reducing the need for a full rebuild.
Combines the best of static content and dynamic updates.
Ensures fast performance and SEO benefits while still keeping content up-to-date.

Cons of ISR:

Slightly more complex to configure than standard SSG.
Not suitable for real-time data or applications requiring updates on every user request.

When to Choose What?

Now that we’ve covered SSR, CSR, SSG, and ISR, how do you choose the best rendering method for your app? Here are some recommendations based on common use cases:

Use SSR if:
- Your app requires real-time or frequently changing data.
- SEO is critical, and you need content to be fully rendered when crawled by search engines.
- You need personalized content for each user.
Use CSR if:
- Your app is highly interactive with a dynamic user interface (e.g., dashboards, SPAs).
- SEO is not a primary concern.
- You want to minimize server load and have a smoother user experience after the initial load.
Use SSG if:
- You have a marketing or e-commerce site with content that doesn’t change frequently.
- SEO is important, and you want to ensure fast load times.
- You prefer content to be pre-rendered ahead of time for optimal performance.
Use ISR if:
- You need to update static content periodically without rebuilding the entire site.
- You have a large site with content that changes at regular intervals (e.g., blog posts, product updates).
- You want to combine the benefits of static pages with the flexibility of background updates.

Conclusion

Choosing the right rendering method in Next.js can have a significant impact on the performance, SEO, and user experience of your application. Whether you’re building a dynamic app with real-time data, a static blog, or an e-commerce site, understanding the differences between SSR, CSR, SSG, and ISR will help you make the right decision for your project. By using these rendering methods strategically, you can ensure that your application performs optimally and meets your users’ needs.

Now that you know when to use each approach, you can confidently choose the best one for your Next.js app and start building high-performance, SEO-friendly websites!