server-side-rendering

🧩 1. What is Client-Side Rendering (CSR)?

In normal React apps (built with create-react-app or similar), the browser:

1. Downloads a mostly empty HTML file.
2. Then downloads a big JavaScript bundle.
3. React runs in the browser to build the visible page (this is called Client-Side Rendering, CSR).

So the user just sees a blank screen for a moment — until React finishes running.

⚙️ Server-Side Rendering (SSR)

With Server-Side Rendering, the server runs the React code first, builds the HTML for the requested page, and sends that ready-to-see HTML to the browser.

So the steps are:

1. User requests example.com/products.
2. The server executes React code, fetches data, and renders full HTML (product list).
3. Browser gets that complete HTML, displays it immediately.
4. Then React’s JavaScript “hydrates” — it attaches event listeners, enabling interactivity.

In short:

• CSR = Browser does all rendering.
• SSR = Server builds the page first → faster visible content, better SEO.

🚀 2. Why SSR is useful

Main benefits:

• Faster initial page load (because the HTML already has content).
• Better SEO (search engines can read HTML content directly).
• Better performance for slow devices (less work on the client).

Downsides:

• Needs a running server (not just static files).
• Slightly higher backend load — server must render on every request.

💡 3. Where Next.js comes in

React itself doesn’t handle how or where rendering happens — it’s just a UI library.

Next.js is a framework built on top of React that:

• Adds server-side rendering (SSR) out of the box.
• Also supports Static Site Generation (SSG) and Client-Side Rendering (CSR) — you can mix all three as needed.
• Provides routing, API routes, and optimizations (image optimization, caching, etc.).

🧱 4. How Next.js does SSR

Example: a Next.js page like pages/users.js:

// pages/users.js
export async function getServerSideProps() {
  const res = await fetch('https://api.example.com/users');
  const users = await res.json();

  return { props: { users } }; // these props go into the React component
}

export default function UsersPage({ users }) {
  return (
    <ul>
      {users.map(user => <li key={user.id}>{user.name}</li>)}
    </ul>
  );
}

• When someone visits /users, Next.js runs getServerSideProps() on the server, fetches data, renders the HTML with that data, and sends it to the browser.
• The user sees a ready-made page instantly.
• Then React hydrates to make it interactive (clicks, etc.).

🧠 5. TL;DR Summary

🎯 6. How to think about it as a developer

Think of Next.js as giving React a brain for how to render — it decides:

• Should this page be pre-built (SSG)?
• Should it be rendered live on the server (SSR)?
• Should it just render on the client (CSR)?

That flexibility is what makes Next.js so powerful in production — you get the developer experience of React, but with speed and SEO benefits like a traditional server-rendered site.

Would you like me to add a quick diagram showing the flow difference between CSR and SSR (React vs Next.js)? It helps visualize what happens under the hood.