Client-Side Rendering
Client-side rendering refers to generating the content on the client’s browser. Clients receive a minimal, empty HTML without any content inside. Afterward, they receive separate JavaScript files that fuel the entire website to generate the content. On the first render, users may experience a loading state on an unmeaningful page. With client-side rendering, users rely mostly on their browsers, making it impractical to ensure good performance on low-end devices. Since the client receives an empty HTML file without any content on the first request, web crawlers struggle to interpret the page’s content and index it properly for optimized search results.
Server-Side Rendering
Server-side rendering refers to generating content and HTML elements on the server side and passing them to the client side. Clients get an immediate experience of meaningful content without any loading period. Since users don’t have to rely heavily on their browsers, they experience smooth performance even on low-spec devices. Server-side rendering not only enhances user experience but also boosts SEO optimizations. It simplifies the process for crawlers to scan the content and index it for optimized search results.
Client-Side Rendering (CSR) vs Server-Side Rendering (SSR)
| Client-Side Rendering (CSR) | Server-Side Rendering (SSR) |
|---|---|
| Receives empty HTML without content on the first request | Receives meaningful content on the first request |
| Content is generated on the client’s browser | Content is generated on the server |
| Users experience a loading state | Users don’t experience a loading state |
| Bad for SEO, as web crawlers receive blank HTML initially | Good for SEO, as crawlers receive meaningful content initially |
| Performance can drop on low-end devices | Optimal performance on both high-end and low-end devices |
Hydration on Server-Side Rendering (SSR)
In server-side rendering, hydration refers to a process quite different from its meaning in real-world scenarios. Typically, hydration means adding water to something. However, in server-side rendering, it means attaching JavaScript to the HTML that the server passes to the client side.
On the first request, the server sends an HTML file with meaningful content. To make the page interactive, it requires JavaScript. After a while, the server sends the necessary JavaScript files to the client. The client uses these files to bind all required event handlers to the DOM elements (HTML elements), making them interactive.
Uncanny Valley
Partial hydration is a technique to avoid the uncanny valley situation and accelerate initial interactivity. Instead of loading the entire JavaScript at once, only the essential JavaScript for specific portions of the page is loaded first, based on priority. This reduces the JavaScript loading time. For example, in a blog post where the comment section needs to be interactive first, the necessary JavaScript file for the comment section loads first, while the rest loads later, based on priority. Popular web frameworks like Next.js and Astro leverage partial hydration to boost website performance.
Conclusion
Choosing between client-side rendering (CSR) and server-side rendering (SSR) depends on your application's needs. Server-side rendering (SSR) ensures faster load times, better SEO, and smoother performance on low-end devices, while client-side rendering (CSR) offers flexibility for dynamic interactions. Hydration on the server side makes pages interactive by attaching JavaScript, and partial hydration further boosts performance by loading only essential scripts first. Frameworks like Next.js and Astro simplify these processes for developers.
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