What Is Next.js? The Beginner’s Guide

What Is Next.js (in plain English)

Next.js is a framework built on React and Node.js that helps you build modern web apps faster (overview). It gives you a full-stack setup in one repo: frontend pages, backend endpoints, and rendering options like SSR and SSG out of the box. That combination is why it is popular for SaaS: good performance, SEO-friendly pages, and backend APIs in a single codebase (why developers use Next.js).

What Next.js Gives You Out of the Box

File-Based Routing

• Routes are created from your file structure (file-based routing).
• Example: pages/about.js becomes /about.

Server-Side Rendering (SSR)

• Pages can be rendered on the server per request (SSR basics).
• This improves first-load speed and SEO. React hydrates on the client for interactivity.

Static Site Generation (SSG)

• Pages can be prebuilt at build time (SSG).
• Great for marketing pages and docs that do not change often.

Built-in API Routes

• Backend endpoints live in the same repo (API routes).
• No separate server required for many projects.

Automatic Code Splitting and Optimization

• Each page ships only the JS/CSS it needs (optimizations).
• Minification, tree-shaking, and image optimization are built in.

Zero-Config DX

• TypeScript, CSS, and Sass support are first-class.
• You can focus on product features instead of setup (DX overview).

Routing and Layouts in Next.js

Next.js maps folders and files to URLs automatically. A nested file like pages/user/settings/notifications.js becomes /user/settings/notifications. Dynamic routes work the same way: [id].js in pages/posts/ maps to /posts/123.

Next.js also supports layouts, which are reusable wrappers for repeated UI. With the App Router, you can define nested layouts per folder, like app/dashboard/layout.js, and every page under /dashboard/* shares it (nested layouts). This is perfect for SaaS apps that have a marketing site and a logged-in dashboard with different chrome.

Server Components vs Client Components (Plain English)

Next.js (especially 13+) distinguishes where a component runs:

Server Components

• Render on the server and send HTML to the browser.
• No client-side JS is shipped for them (server vs client components).
• Good for fast, secure data rendering and static UI.

Client Components

• Run in the browser and enable interactivity.
• Require the "use client" directive at the top of the file (client components).
• Needed for click handlers, form state, charts, animations, etc.

In practice, pages are often a mix: server components for the main layout and data, client components for interactive widgets. This hybrid approach gives you speed and security without losing UX.

Built-in API Routes: Your Backend in the Same Repo

Next.js lets you define backend endpoints right next to your UI. Any file under pages/api/ (Pages Router) or app/api/ (App Router) becomes an HTTP endpoint. For example:

// pages/api/hello.js
export default function handler(req, res) {
  res.status(200).json({ greeting: "Hello from Next API" });
}

Now a request to /api/hello runs that code on the server and returns JSON. These routes become serverless functions when deployed to platforms like Vercel. The code in pages/api is never sent to the browser (API routes are server-only), so you can safely keep secrets and connect to databases.

A quick exercise: run pnpm dev, then visit http://localhost:3000/api/health (after creating api/health). If you see { "status": "ok" }, you just proved your frontend and backend are running in the same app.

This is why many teams start with a single Next.js repo. It keeps UI and API in sync, avoids CORS issues, and lets you share types and config. If you later outgrow API routes, you can still introduce a dedicated backend service and call it from Next.js. It is not all-or-nothing.

Tradeoffs: When You Might Not Need Next.js

Next.js is powerful, but it is not mandatory for every project:

• Very simple sites: a single static landing page might be simpler with plain HTML or Vite. Next.js can feel like overkill for tiny projects, even though it scales well (is it overkill?).
• Already have a backend: if you only need a client-side UI and do not care about SSR/SEO, a lighter React setup can work. Still, using Next.js is fine if you want conventions.
• Specialized backends: if you need heavy data processing, microservices, or multiple frontends sharing one API, you might add a separate backend and use Next.js mainly for the UI (separate backend?).

That said, many SaaS apps start and scale with Next.js alone. For example, sushi-templates.com uses Next.js for both frontend and backend. The framework gives you a full-stack workflow and lets you add external services only when needed (why it’s a game-changer).

Conclusion & Next Steps

Next.js offers a beginner-friendly yet powerful way to build web applications. It streamlines routing, rendering, and backend APIs in one codebase so you can focus on product features instead of plumbing.

If you want to try it:

1. Create a project with npx create-next-app@latest or a team template.
2. Run pnpm dev.
3. Add a simple api/health route and open http://localhost:3000/api/health.

From there, build pages with file-based routing, use server components for fast data rendering, and add client components where you need interactivity. Next.js handles the rest.

References

• Contentful Blog – Next.js vs React: https://www.contentful.com/blog/next-js-vs-react/
• Dev.to – Next.js overview and tradeoffs: https://dev.to/hamzakhan/why-nextjs-is-an-all-time-game-changer-for-web-development-a-technical-perspective-1bgf
• Reddit r/nextjs discussion (features): https://www.reddit.com/r/nextjs/comments/v01uy1/why_should_i_use_next_other_than_ssr/
• Stack Overflow – Next vs separate backend: https://stackoverflow.com/questions/78349307/ssr-and-api-layer-in-nextjs
• LogRocket – Next.js layouts: https://blog.logrocket.com/guide-next-js-layouts-nested-layouts/
• Dev.to – Server vs client components: https://dev.to/oskarinmix/server-components-vs-client-components-in-nextjs-differences-pros-and-cons-389f