Next.js Complete Guide: From Beginner to Expert with Code Structure

Next.js has become the go-to framework for building production-ready React applications. This comprehensive guide will take you from absolute beginner to expert level, covering everything you need to know about Next.js with practical code examples and best practices.

1. [Getting Started (Beginner)](#getting-started)

2. [Core Concepts](#core-concepts)

3. [Routing & Navigation](#routing--navigation)

4. [Data Fetching](#data-fetching)

5. [Styling & UI](#styling--ui)

6. [Optimization (Intermediate)](#optimization)

7. [Advanced Patterns (Expert)](#advanced-patterns)

8. [Production Code Structure](#production-code-structure)

9. [Deployment & Performance](#deployment--performance)

---

Getting Started (Beginner)

What is Next.js?

Next.js is a React framework that provides:

Server-Side Rendering (SSR) - Render pages on the server

Static Site Generation (SSG) - Pre-render pages at build time

API Routes - Build backend APIs alongside your frontend

File-based Routing - Automatic routing based on file structure

Built-in Optimizations - Image optimization, code splitting, and more

Installation

bash

1# Create a new Next.js app
2npx create-next-app@latest my-app
3 
4# Or with TypeScript
5npx create-next-app@latest my-app --typescript
6 
7# Or with specific options
8npx create-next-app@latest my-app --typescript --tailwind --app

Project Structure (Basic)

text

1my-app/
2├── app/                 # App Router (Next.js 13+)
3│   ├── layout.js       # Root layout
4│   ├── page.js         # Home page
5│   └── globals.css     # Global styles
6├── public/             # Static files
7├── next.config.js      # Next.js configuration
8└── package.json        # Dependencies

Your First Page

javascript

1// app/page.js
2export default function Home() {
3  return (
4    <div>
5      <h1>Welcome to Next.js!</h1>
6      <p>This is your first page.</p>
7    </div>
8  );
9}

---

Core Concepts

Pages vs App Router

Next.js offers two routing systems:

Pages Router (Traditional)

text

1pages/
2├── index.js          # Home page (/)
3├── about.js          # About page (/about)
4└── blog/
5    └── [slug].js     # Dynamic route (/blog/:slug)

App Router (Next.js 13+)

text

1app/
2├── page.js           # Home page (/)
3├── about/
4│   └── page.js       # About page (/about)
5└── blog/
6    └── [slug]/
7        └── page.js   # Dynamic route (/blog/:slug)

Server Components vs Client Components

Server Component (Default)

javascript

1// app/components/ServerComponent.js
2// Runs on the server - no 'use client' directive
3export default function ServerComponent() {
4  // Can directly access databases, APIs, etc.
5  const data = fetch('https://api.example.com/data');
6  
7  return <div>{/* Rendered on server */}</div>;
8}

Client Component

javascript

1// app/components/ClientComponent.js
2'use client'; // Required for client-side interactivity
3 
4import { useState } from 'react';
5 
6export default function ClientComponent() {
7  const [count, setCount] = useState(0);
8  
9  return (
10    <button onClick={() => setCount(count + 1)}>
11      Count: {count}
12    </button>
13  );
14}

---

Routing & Navigation

Basic Routing

javascript

1// app/about/page.js
2export default function About() {
3  return <h1>About Page</h1>;
4}

Dynamic Routes

javascript

1// app/blog/[slug]/page.js
2export default function BlogPost({ params }) {
3  return <h1>Blog Post: {params.slug}</h1>;
4}

Nested Dynamic Routes

javascript

1// app/shop/[...slug]/page.js
2// Matches /shop, /shop/a, /shop/a/b, etc.
3export default function Shop({ params }) {
4  return <div>Shop: {params.slug.join('/')}</div>;
5}

Navigation

javascript(21 lines, showing 15)

1'use client';
2 
3import Link from 'next/link';
4import { useRouter } from 'next/navigation';
5 
6export default function Navigation() {
7  const router = useRouter();
8  
9  return (
10    <nav>
11      {/* Client-side navigation */}
12      <Link href="/about">About</Link>
13      <Link href="/blog/post-1">Blog Post</Link>
14      
15      {/* Programmatic navigation */}

Route Groups

javascript

1// app/(marketing)/about/page.js
2// app/(marketing)/contact/page.js
3// app/(shop)/products/page.js
4// Groups don't affect URL structure

---

Data Fetching

Server Components - Direct Fetching

javascript(16 lines, showing 15)

1// app/posts/page.js
2export default async function Posts() {
3  // Fetch data directly in Server Component
4  const res = await fetch('https://api.example.com/posts', {
5    cache: 'no-store' // Always fetch fresh data
6  });
7  const posts = await res.json();
8  
9  return (
10    <ul>
11      {posts.map(post => (
12        <li key={post.id}>{post.title}</li>
13      ))}
14    </ul>
15  );

Caching Strategies

javascript

1// Time-based revalidation
2fetch(url, { next: { revalidate: 3600 } }); // Revalidate every hour
3 
4// Force dynamic
5fetch(url, { cache: 'no-store' });
6 
7// Force static
8fetch(url, { cache: 'force-cache' });

Client-Side Data Fetching

javascript(27 lines, showing 15)

1'use client';
2 
3import { useEffect, useState } from 'react';
4 
5export default function ClientPosts() {
6  const [posts, setPosts] = useState([]);
7  const [loading, setLoading] = useState(true);
8  
9  useEffect(() => {
10    fetch('/api/posts')
11      .then(res => res.json())
12      .then(data => {
13        setPosts(data);
14        setLoading(false);
15      });

Using SWR (Recommended for Client Fetching)

bash

1npm install swr

javascript(20 lines, showing 15)

1'use client';
2 
3import useSWR from 'swr';
4 
5const fetcher = (url) => fetch(url).then(res => res.json());
6 
7export default function Posts() {
8  const { data, error, isLoading } = useSWR('/api/posts', fetcher);
9  
10  if (error) return <div>Failed to load</div>;
11  if (isLoading) return <div>Loading...</div>;
12  
13  return (
14    <ul>
15      {data.map(post => (

---

Styling & UI

CSS Modules

javascript

1// app/components/Button.module.css
2.button {
3  background: blue;
4  color: white;
5  padding: 10px 20px;
6}

javascript

1// app/components/Button.js
2import styles from './Button.module.css';
3 
4export default function Button() {
5  return <button className={styles.button}>Click me</button>;
6}

Tailwind CSS

javascript

1// app/components/Card.js
2export default function Card({ title, children }) {
3  return (
4    <div className="bg-white rounded-lg shadow-md p-6">
5      <h2 className="text-2xl font-bold mb-4">{title}</h2>
6      {children}
7    </div>
8  );
9}

Styled Components

bash

1npm install styled-components

javascript

1'use client';
2 
3import styled from 'styled-components';
4 
5const StyledButton = styled.button`
6  background: ${props => props.primary ? 'blue' : 'gray'};
7  color: white;
8  padding: 10px 20px;
9  border: none;
10  border-radius: 4px;
11`;
12 
13export default function Button({ primary, children }) {
14  return <StyledButton primary={primary}>{children}</StyledButton>;
15}

---

Optimization (Intermediate)

Image Optimization

javascript

1import Image from 'next/image';
2 
3export default function OptimizedImage() {
4  return (
5    <Image
6      src="/hero.jpg"
7      alt="Hero image"
8      width={800}
9      height={600}
10      priority // Load immediately
11      placeholder="blur" // Blur placeholder
12    />
13  );
14}

Font Optimization

javascript

1// app/layout.js
2import { Inter } from 'next/font/google';
3 
4const inter = Inter({ subsets: ['latin'] });
5 
6export default function RootLayout({ children }) {
7  return (
8    <html lang="en" className={inter.className}>
9      <body>{children}</body>
10    </html>
11  );
12}

Code Splitting

javascript

1'use client';
2 
3import dynamic from 'next/dynamic';
4 
5// Lazy load component
6const HeavyComponent = dynamic(() => import('./HeavyComponent'), {
7  loading: () => <p>Loading...</p>,
8  ssr: false // Disable SSR if needed
9});
10 
11export default function Page() {
12  return <HeavyComponent />;
13}

Metadata & SEO

javascript

1// app/about/page.js
2export const metadata = {
3  title: 'About Us',
4  description: 'Learn more about our company',
5  openGraph: {
6    title: 'About Us',
7    description: 'Learn more about our company',
8    images: ['/og-image.jpg'],
9  },
10};
11 
12export default function About() {
13  return <h1>About</h1>;
14}

---

Advanced Patterns (Expert)

Server Actions

javascript

1// app/actions.js
2'use server';
3 
4export async function createPost(formData) {
5  const title = formData.get('title');
6  const content = formData.get('content');
7  
8  // Save to database
9  await db.posts.create({ title, content });
10  
11  revalidatePath('/posts');
12  redirect('/posts');
13}

javascript

1// app/posts/new/page.js
2import { createPost } from '../actions';
3 
4export default function NewPost() {
5  return (
6    <form action={createPost}>
7      <input name="title" required />
8      <textarea name="content" required />
9      <button type="submit">Create Post</button>
10    </form>
11  );
12}

Middleware

javascript(17 lines, showing 15)

1// middleware.js
2import { NextResponse } from 'next/server';
3 
4export function middleware(request) {
5  // Authentication check
6  const token = request.cookies.get('token');
7  
8  if (!token && request.nextUrl.pathname.startsWith('/dashboard')) {
9    return NextResponse.redirect(new URL('/login', request.url));
10  }
11  
12  return NextResponse.next();
13}
14 
15export const config = {

API Routes

javascript

1// app/api/posts/route.js
2export async function GET(request) {
3  const posts = await db.posts.findMany();
4  return Response.json(posts);
5}
6 
7export async function POST(request) {
8  const body = await request.json();
9  const post = await db.posts.create({ data: body });
10  return Response.json(post, { status: 201 });
11}

Streaming & Suspense

javascript(25 lines, showing 15)

1// app/dashboard/page.js
2import { Suspense } from 'react';
3 
4async function UserProfile() {
5  const user = await fetchUser();
6  return <div>{user.name}</div>;
7}
8 
9async function UserPosts() {
10  const posts = await fetchPosts();
11  return <ul>{posts.map(p => <li key={p.id}>{p.title}</li>)}</ul>;
12}
13 
14export default function Dashboard() {
15  return (

Error Boundaries

javascript

1// app/error.js
2'use client';
3 
4export default function Error({ error, reset }) {
5  return (
6    <div>
7      <h2>Something went wrong!</h2>
8      <button onClick={() => reset()}>Try again</button>
9    </div>
10  );
11}

Loading States

javascript

1// app/loading.js
2export default function Loading() {
3  return <div>Loading...</div>;
4}

---

Production Code Structure

Recommended Folder Structure

text(31 lines, showing 15)

1my-app/
2├── app/
3│   ├── (auth)/
4│   │   ├── login/
5│   │   └── register/
6│   ├── (dashboard)/
7│   │   ├── dashboard/
8│   │   └── settings/
9│   ├── api/
10│   │   ├── auth/
11│   │   └── posts/
12│   ├── components/
13│   │   ├── ui/
14│   │   ├── forms/
15│   │   └── layout/

Component Organization

javascript(23 lines, showing 15)

1// app/components/ui/Button.js
2'use client';
3 
4export default function Button({ 
5  children, 
6  variant = 'primary',
7  onClick 
8}) {
9  const baseStyles = 'px-4 py-2 rounded font-medium';
10  const variants = {
11    primary: 'bg-blue-600 text-white hover:bg-blue-700',
12    secondary: 'bg-gray-200 text-gray-800 hover:bg-gray-300',
13  };
14  
15  return (

Utility Functions

javascript

1// app/lib/utils.js
2export function formatDate(date) {
3  return new Intl.DateTimeFormat('en-US', {
4    year: 'numeric',
5    month: 'long',
6    day: 'numeric',
7  }).format(new Date(date));
8}
9 
10export function cn(...classes) {
11  return classes.filter(Boolean).join(' ');
12}

Database Layer

javascript

1// app/lib/db.js
2import { PrismaClient } from '@prisma/client';
3 
4const globalForPrisma = globalThis;
5 
6export const db = globalForPrisma.prisma || new PrismaClient();
7 
8if (process.env.NODE_ENV !== 'production') {
9  globalForPrisma.prisma = db;
10}

Environment Variables

javascript

1// .env.local
2DATABASE_URL="postgresql://..."
3NEXT_PUBLIC_API_URL="https://api.example.com"
4SECRET_KEY="your-secret-key"

javascript

1// app/lib/config.js
2export const config = {
3  apiUrl: process.env.NEXT_PUBLIC_API_URL,
4  secretKey: process.env.SECRET_KEY,
5};

---

Deployment & Performance

Build Optimization

javascript(24 lines, showing 15)

1// next.config.js
2/** @type {import('next').NextConfig} */
3const nextConfig = {
4  // Enable SWC minification
5  swcMinify: true,
6  
7  // Optimize images
8  images: {
9    domains: ['example.com'],
10  },
11  
12  // Compression
13  compress: true,
14  
15  // Production source maps

Performance Monitoring

javascript

1// app/instrumentation.js
2export async function register() {
3  if (process.env.NEXT_RUNTIME === 'nodejs') {
4    await import('./lib/monitoring');
5  }
6}

Deployment Checklist

[ ] Set environment variables

[ ] Optimize images

[ ] Enable compression

[ ] Set up error tracking (Sentry)

[ ] Configure analytics

[ ] Set up CDN

[ ] Enable caching headers

[ ] Test production build locally

[ ] Set up monitoring

Vercel Deployment

bash

1# Install Vercel CLI
2npm i -g vercel
3 
4# Deploy
5vercel
6 
7# Production deployment
8vercel --prod

---

Best Practices Summary

Do's ✅

Use Server Components by default

Leverage Next.js Image component

Implement proper error boundaries

Use TypeScript for type safety

Optimize bundle size

Implement proper caching strategies

Use middleware for authentication

Follow the file-based routing conventions

Don'ts ❌

Don't use 'use client' unnecessarily

Don't fetch data in Client Components when Server Components can do it

Don't ignore SEO metadata

Don't skip error handling

Don't forget to optimize images

Don't use inline styles for everything

Don't ignore accessibility

---

Resources

[Next.js Documentation](https://nextjs.org/docs)

[Next.js GitHub](https://github.com/vercel/next.js)

[React Documentation](https://react.dev)

[Vercel Platform](https://vercel.com)

---

Conclusion

Next.js is a powerful framework that simplifies React development while providing excellent performance out of the box. By following this guide, you've learned:

1. Basics: Setup, routing, and core concepts

2. Intermediate: Data fetching, styling, and optimization

3. Advanced: Server actions, middleware, and streaming

4. Expert: Production structure and deployment

Start building your Next.js application today and experience the power of modern web development!

Happy coding! 🚀

Next.js Complete Guide: From Beginner to Expert with Code Structure

Table of Contents

Getting Started (Beginner)

What is Next.js?

Installation

Project Structure (Basic)

Your First Page

Core Concepts

Pages vs App Router

Server Components vs Client Components

Routing & Navigation

Basic Routing

Dynamic Routes

Nested Dynamic Routes

Navigation

Route Groups

Data Fetching

Server Components - Direct Fetching

Caching Strategies

Client-Side Data Fetching

Using SWR (Recommended for Client Fetching)

Styling & UI

CSS Modules

Tailwind CSS

Styled Components

Optimization (Intermediate)

Image Optimization

Font Optimization

Code Splitting

Metadata & SEO

Advanced Patterns (Expert)

Server Actions

Middleware

API Routes

Streaming & Suspense

Error Boundaries

Loading States

Production Code Structure

Recommended Folder Structure

Component Organization

Utility Functions

Database Layer

Environment Variables

Deployment & Performance

Build Optimization

Performance Monitoring

Deployment Checklist

Vercel Deployment

Best Practices Summary

Do's ✅

Don'ts ❌

Resources

Conclusion

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