Next.js: What is this React framework?

What is Next.js?

Next.js is a React framework created by Vercel (formerly Zeit) in 2016. It extends React's capabilities by adding server-side rendering (SSR), static site generation (SSG), file-system-based routing, and since version 13, React Server Components via its App Router. Next.js has become the most popular React framework, with over 120,000 stars on GitHub.

The fundamental problem Next.js solves is React application rendering. By default, React operates in SPA (Single Page Application) mode: the browser downloads a JavaScript bundle that generates HTML on the client side. This approach creates problems with SEO (search engines struggle to index JavaScript-generated content), initial performance (content only appears after JavaScript loads), and user experience on slow connections.

Next.js solves these problems by allowing developers to choose, page by page, the most appropriate rendering strategy: SSR for dynamic content that changes with each request, SSG for pages whose content does not change frequently, ISR (Incremental Static Regeneration) for a compromise between the two, or classic client-side rendering for highly interactive interfaces.

Why Next.js matters

Next.js has fundamentally changed how JavaScript developers build web applications. Its importance in the React ecosystem has grown to the point where the official React documentation recommends Next.js as the starting point for new applications.

• Hybrid rendering: the ability to mix SSR, SSG, ISR, and client rendering in the same application offers unparalleled flexibility to optimize performance and SEO on a page-by-page basis.
• App Router and Server Components: the App Router introduced in Next.js 13 uses React Server Components to drastically reduce the amount of JavaScript sent to the browser. Server components execute only on the server and send pure HTML to the client.
• Automatic optimizations: Next.js automatically optimizes images (next/image), fonts (next/font), third-party scripts, and code-splitting. These optimizations significantly improve Core Web Vitals without additional developer effort.
• API Routes: Next.js allows creating API endpoints directly within the project, without a separate backend server. This feature is useful for simple serverless functions like form submissions or webhooks.
• Simplified deployment: Vercel, the company behind Next.js, offers a deployment platform optimized for the framework, with automatic preview deployments, edge functions, and a global CDN.

How it works

Next.js architecture is based on the concept of pages. In the Pages Router (legacy), each file in the pages/ directory automatically becomes a route. A file pages/about.js creates the /about route. In the new App Router, the structure is based on directories within app/ with conventional files like page.js, layout.js, and loading.js.

Server-side rendering works as follows: when a user accesses an SSR page, the Next.js server executes the React component, generates the complete HTML, and sends it to the browser. The browser immediately displays the HTML content, then React takes over to hydrate the page and add JavaScript interactivity. This mechanism ensures fast display while retaining the richness of a React application.

Static generation (SSG) works at build time: Next.js executes the components, generates static HTML pages, and deploys them to a CDN. Pages load instantly because there is no server computation required. ISR allows regenerating these pages in the background after a configurable delay, combining the advantages of static generation with up-to-date content.

Server Components allow executing React components exclusively on the server. They can directly access the database, file system, and internal APIs without exposing sensitive code to the browser. Only the resulting HTML is transmitted to the client, significantly reducing the JavaScript bundle size.

Real-world example

Vercel.com, the company's own website, is obviously built with Next.js. But beyond that, companies like TikTok, Twitch, Hulu, Nike, and HashiCorp's documentation use Next.js in production for very high-traffic sites.

A common use case is creating an e-commerce site: product pages are generated with SSG for optimal performance, search pages use SSR for dynamic and personalized content, and the shopping cart works with client-side rendering for maximum interactivity.

Another typical example is developing an analytics dashboard: Server Components load data directly from the database, interactive charts are rendered client-side, and API routes handle authentication and data exports.

Implementation

1. Installation: create a project with npx create-next-app@latest. The interactive wizard lets you choose TypeScript, TailwindCSS, ESLint, and the router type (App Router or Pages Router).
2. Structure: organize your code with the App Router in the app/ directory. Each route is a folder containing a page.tsx file for content and optionally layout.tsx for layout.
3. Data fetching: use async functions directly in Server Components to load data. For dynamic data, use revalidation options to control refresh frequency.
4. Styling: Next.js natively supports CSS Modules, Tailwind CSS, CSS-in-JS, and Sass. Tailwind CSS is the most popular choice in the Next.js ecosystem.
5. Optimization: use the Image component for images, Font for fonts, and Script for third-party scripts. These components include automatic performance optimizations.
6. Deployment: deploy to Vercel for an optimal experience, or use Docker and Node.js for self-hosted deployment on any infrastructure.

Associated technologies and tools

• React: the JavaScript library on which Next.js is built. React proficiency is a prerequisite for using Next.js.
• TypeScript: the language of choice in the Next.js ecosystem, offering static typing that improves code reliability.
• Tailwind CSS: utility-first CSS framework, the natural companion to Next.js for component styling.
• Vercel: deployment platform created by the makers of Next.js, optimized for its features.
• Prisma: TypeScript/JavaScript ORM often used with Next.js to interact with the database.
• NextAuth.js: authentication solution dedicated to Next.js, supporting OAuth, credentials, and JWT.

Conclusion

Next.js has become the reference for building React applications in production. Its rendering flexibility, automatic optimizations, and the Vercel ecosystem make it a powerful tool for demanding frontend projects. However, Next.js is primarily a frontend framework: for complex business logic, advanced data management, and robust backend processes, it often needs to be paired with a dedicated backend. At KERN-IT, we combine React on the frontend with Django on the backend to offer the best of both worlds: a reactive, performant user interface backed by a solid, extensible Python backend capable of handling business logic, APIs, AI, and data processing.