Next.js in 2025: Mastering the App Router

Next.js continues to dominate the React framework landscape in 2025. The App Router, built on top of React Server Components, is now the standard for building new applications. This tutorial covers the modern way to build with Next.js.

The App Router

The `app` directory introduces a new file-system-based routing paradigm. Folders define routes, and special files like `page.js`, `layout.js`, and `loading.js` define the UI for that route.

Server Components vs. Client Components

By default, all components in the App Router are React Server Components (RSCs). They run on the server, allowing you to fetch data directly and securely. For interactivity, you use the `"use client"` directive to create Client Components.

// app/page.js - A Server Component
async function getData() {
  const res = await fetch('https://api.example.com/posts');
  return res.json();
}

export default async function Page() {
  const posts = await getData();
  return <main>{/* Render posts */} </main>;
}

Data Fetching

Data fetching is now done directly in Server Components using `async/await` with `fetch`. Next.js automatically dedupes requests and provides powerful caching and revalidation options.