Part 3: Understanding Pre-Rendering in Next.js: How It Works

[Page] Getting Started

In the world of web development, Next.js stands out by offering pre-rendering capabilities that transform how React components are served to users. This blog post will delve into the mechanics of pre-rendering in Next.js, explaining how components are rendered on the server and how this process differs between development and production modes.

How Does Pre-Rendering Work?

In a Next.js application, components like our HomePage are pre-rendered, meaning that the HTML returned by the server already includes the elements defined in the component. But how exactly does this happen?

Server-Side Rendering

When you develop with Next.js, your components are rendered on the server. To illustrate this, you can add a simple log statement inside your component function to see when it's rendered:

// File: pages/index.js
function HomePage() {
  console.log('[HomePage] render');
  return (
    <main>
      <h1>My Blog</h1>
    </main>
  );
}

export default HomePage;

In development mode, you'll notice that the "render" message appears both in the server logs and the browser console. This indicates that the component is rendered twice: once on the server to generate the HTML and once in the browser for client-side interactivity.

Client-Side Rendering

The second rendering in the browser allows for client-side functionality, such as handling user interactions. This dual rendering ensures that while the server provides a static HTML structure, the browser can enhance the page with interactive features.

Development vs. Production Mode

In development mode, Next.js re-renders components every time you reload the page. This ensures that any code changes are reflected immediately. However, in production mode, the process is optimized for performance.

Building for Production

To run a Next.js app in production mode, you'll need to build the application first. Here's how you can set up your package.json to include build and start scripts:

// File: package.json
{
  "name": "next-blog",
  "private": true,
  "scripts": {
    "build": "next build",
    "dev": "next dev",
    "start": "next start"
  },
  "dependencies": {
    "next": "^14.0.0",
    "react": "^18.0.0",
    "react-dom": "^18.0.0"
  }
}

You can then create a production build with:

npm run build

During this build process, Next.js generates static HTML pages. The server can serve these pre-rendered pages directly, without re-rendering them on each request:

npm start

Static Pages

In production mode, Next.js serves static HTML files generated during the build step. These files are stored in the .next directory and include your pre-rendered components:

.next/
└── server/
    └── pages/
        └── index.html

This index.html file contains the pre-rendered HTML for your HomePage, allowing the server to quickly deliver the page without additional computation.

Conclusion

Next.js's ability to pre-render React components on the server provides significant performance benefits and improves SEO. By understanding the differences between development and production modes, you can effectively utilize Next.js to build fast, scalable web applications. Keep in mind that while development mode offers flexibility for testing and debugging, production mode optimizes delivery by serving static pages generated at build time. This dual approach ensures that your applications are both performant and interactive.