If you’ve started working with Next.js or heard about it in the JavaScript ecosystem, you've likely come across terms like CSR, SSR, SSG, and ISR. These may sound complex at first, but they are just different ways to render pages in Next.js, each with its own advantages and use cases. Each of these methods affect how your Next.js app builds, serves, and displays content, impacting speed, SEO, and user experience. Let’s explore each in detail with examples to understand how they work and when they make sense.

Client-Side Rendering (CSR)

Client-Side Rendering is a method where the browser (client) handles most of the work.
How it Works: In CSR, when a user visits a page, the server initially sends an empty HTML file. Then the build process (painting process) of how the web page will look happens on the client side itself.
Use case: SaaS dashboards. Since they are not intended for Google indexing, there’s no need to place unnecessary load on the server. Instead, this load can be efficiently handled on the client side itself.
Pro: Good for interactive pages where content changes frequently.
Con: Since initial HTML is empty, it’s less SEO-friendly. Search engines don’t “see” much content until JavaScript kicks in, making it harder for pages to rank.

Server-Side Rendering (SSR)

Server-Side Rendering is a big improvement for situations where SEO and fast loading are important.
How it Works: In SSR, when a user visits a page, the server pre-renders the entire HTML file for that page, including content. The server handles rendering, then sends the complete HTML to the client.
Use case: A news website could use SSR to ensure that all article content is ready to read as soon as the page loads. The server sends the rendered HTML, and JavaScript then takes over for further interactions.
Pros and Cons:
Pro: It boosts SEO since the HTML content is already present when it reaches the client.
Con: It can increase server load because each request generates a new HTML file on the fly.

Static Site Generation (SSG)

Static Site Generation prepares pages at build time. It’s a great choice for content that doesn’t change often.
How it Works: With SSG, the HTML for each page is pre-rendered at build time (when you deploy your app). These pages are then served as static HTML files to every visitor, resulting in fast loading.
Use case: SSG is a great option for blogs, portfolios, documentation sites, or any other content that rarely updates and can benefit from super-fast loading times.
Pros and Cons:
Pro: Incredibly fast because pages are ready to go. Minimal server load.
Con: Not suitable for content that changes often since you’d have to rebuild the site to update content.

Incremental Static Regeneration (ISR)

Incremental Static Regeneration is Next.js’s way of combining the best parts of static and dynamic content. This combines the speed of SSG with the flexibility of SSR!
How it Works: ISR lets you set up intervals for like every hour or every few seconds at which Next.js will regenerate specific pages in the background. When new content is available, ISR triggers a build of just the changed content instead of rebuilding the entire site.
Use case: ISR is ideal for e-commerce product listings because it provides fast-loading pages with product details while periodically updating stock and price changes. This approach offers users a smooth browsing experience with up-to-date information, without high server costs.
Pros and Cons:
Pro: It’s a powerful option for dynamic sites with high traffic, as users get nearly static load speeds but with refreshed content.
Con: It can sometimes show outdated content until the page regenerates, and it may introduce some extra server costs and complexity compared to static sites. It’s ideal for semi-dynamic content but not real-time updates.

Choosing between CSR, SSR, SSG, and ISR isn’t about picking the “best” one—each has its purpose. It’s all about understanding your project’s specific needs and how frequently content will change. Combining these techniques provide an amazing way of getting the best of both worlds, be it website performance or SEO.

Happy coding! Let me know in the comments if there’s a rendering strategy that works best for your projects.