nextjs

Guide for implementing Next.js - a React framework for production with server-side rendering, static generation, and modern web features. Use when building Next.js applications, implementing App Router, working with server components, data fetching, routing, or optimizing performance.

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Next.js Skill

Next.js is a React framework for building full-stack web applications with server-side rendering, static generation, and powerful optimization features built-in.

Reference

https://nextjs.org/docs/llms.txt

When to Use This Skill

Use this skill when:

Building new Next.js applications (v15+)
Implementing App Router architecture
Working with Server Components and Client Components
Setting up routing, layouts, and navigation
Implementing data fetching patterns
Optimizing images, fonts, and performance
Configuring metadata and SEO
Setting up API routes and route handlers
Migrating from Pages Router to App Router
Deploying Next.js applications

Core Concepts

App Router vs Pages Router

App Router (Recommended for v13+):

Modern architecture with React Server Components
File-system based routing in app/ directory
Layouts, loading states, and error boundaries
Streaming and Suspense support
Nested routing with layouts

Pages Router (Legacy):

Traditional page-based routing in pages/ directory
Uses getStaticProps, getServerSideProps, getInitialProps
Still supported for existing projects

Key Architectural Principles

Server Components by Default: Components in app/ are Server Components unless marked with 'use client'
File-based Routing: File system defines application routes
Nested Layouts: Share UI across routes with layouts
Progressive Enhancement: Works without JavaScript when possible
Automatic Optimization: Images, fonts, scripts auto-optimized

Installation & Setup

Create New Project

npx create-next-app@latest my-app
# or
yarn create next-app my-app
# or
pnpm create next-app my-app
# or
bun create next-app my-app

Interactive Setup Prompts:

TypeScript? (Yes recommended)
ESLint? (Yes recommended)
Tailwind CSS? (Optional)
src/ directory? (Optional)
App Router? (Yes for new projects)
Import alias? (Default: @/*)

Manual Setup

npm install next@latest react@latest react-dom@latest

package.json scripts:

{
  "scripts": {
    "dev": "next dev",
    "build": "next build",
    "start": "next start",
    "lint": "next lint"
  }
}

Project Structure

my-app/
├── app/                    # App Router (v13+)
│   ├── layout.tsx         # Root layout
│   ├── page.tsx           # Home page
│   ├── loading.tsx        # Loading UI
│   ├── error.tsx          # Error UI
│   ├── not-found.tsx      # 404 page
│   ├── global.css         # Global styles
│   └── [folder]/          # Route segments
├── public/                # Static assets
├── components/            # React components
├── lib/                   # Utility functions
├── next.config.js         # Next.js configuration
├── package.json
└── tsconfig.json

Routing

File Conventions

page.tsx - Page UI for route
layout.tsx - Shared UI for segment and children
loading.tsx - Loading UI (wraps page in Suspense)
error.tsx - Error UI (wraps page in Error Boundary)
not-found.tsx - 404 UI
route.ts - API endpoint (Route Handler)
template.tsx - Re-rendered layout UI
default.tsx - Parallel route fallback

Basic Routing

Static Route:

app/
├── page.tsx              → /
├── about/
│   └── page.tsx         → /about
└── blog/
    └── page.tsx         → /blog

Dynamic Route:

// app/blog/[slug]/page.tsx
export default function BlogPost({ params }: { params: { slug: string } }) {
  return <h1>Post: {params.slug}</h1>
}

Catch-all Route:

// app/shop/[...slug]/page.tsx
export default function Shop({ params }: { params: { slug: string[] } }) {
  return <h1>Category: {params.slug.join('/')}</h1>
}

Optional Catch-all:

// app/docs/[[...slug]]/page.tsx
// Matches /docs, /docs/a, /docs/a/b, etc.

Route Groups

Organize routes without affecting URL:

app/
├── (marketing)/          # Group without URL segment
│   ├── about/page.tsx   → /about
│   └── blog/page.tsx    → /blog
└── (shop)/
    ├── products/page.tsx → /products
    └── cart/page.tsx     → /cart

Parallel Routes

Render multiple pages in same layout:

app/
├── @team/               # Slot
│   └── page.tsx
├── @analytics/          # Slot
│   └── page.tsx
└── layout.tsx           # Uses both slots

// app/layout.tsx
export default function Layout({
  children,
  team,
  analytics,
}: {
  children: React.ReactNode
  team: React.ReactNode
  analytics: React.ReactNode
}) {
  return (
    <>
      {children}
      {team}
      {analytics}
    </>
  )
}

Intercepting Routes

Intercept routes to show in modal:

app/
├── feed/
│   └── page.tsx
├── photo/
│   └── [id]/
│       └── page.tsx
└── (..)photo/           # Intercepts /photo/[id]
    └── [id]/
        └── page.tsx

Layouts

Root Layout (Required)

// app/layout.tsx
export default function RootLayout({
  children,
}: {
  children: React.ReactNode
}) {
  return (
    <html lang="en">
      <body>{children}</body>
    </html>
  )
}

Nested Layouts

// app/dashboard/layout.tsx
export default function DashboardLayout({
  children,
}: {
  children: React.ReactNode
}) {
  return (
    <section>
      <nav>Dashboard Nav</nav>
      {children}
    </section>
  )
}

Layouts are:

Shared across multiple pages
Preserve state on navigation
Do not re-render on navigation
Can fetch data

Server and Client Components

Server Components (Default)

Components in app/ are Server Components by default:

// app/page.tsx (Server Component)
async function getData() {
  const res = await fetch('https://api.example.com/data')
  return res.json()
}

export default async function Page() {
  const data = await getData()
  return <div>{data.title}</div>
}

Benefits:

Fetch data on server
Access backend resources directly
Keep sensitive data on server
Reduce client-side JavaScript
Improve initial page load

Limitations:

Cannot use hooks (useState, useEffect)
Cannot use browser APIs
Cannot add event listeners

Client Components

Mark components with 'use client' directive:

// components/counter.tsx
'use client'

import { useState } from 'react'

export function Counter() {
  const [count, setCount] = useState(0)

  return (
    <button onClick={() => setCount(count + 1)}>
      Count: {count}
    </button>
  )
}

Use Client Components for:

Interactive UI (onClick, onChange)
State management (useState, useReducer)
Effects (useEffect, useLayoutEffect)
Browser APIs (localStorage, navigator)
Custom hooks
React class components

Composition Pattern

// app/page.tsx (Server Component)
import { ClientComponent } from './client-component'

export default function Page() {
  return (
    <div>
      <h1>Server-rendered content</h1>
      <ClientComponent />
    </div>
  )
}

Data Fetching

Server Component Data Fetching

// app/posts/page.tsx
async function getPosts() {
  const res = await fetch('https://api.example.com/posts', {
    next: { revalidate: 3600 } // Revalidate every hour
  })

  if (!res.ok) throw new Error('Failed to fetch')

  return res.json()
}

export default async function PostsPage() {
  const posts = await getPosts()

  return (
    <ul>
      {posts.map(post => (
        <li key={post.id}>{post.title}</li>
      ))}
    </ul>
  )
}

Caching Strategies

Force Cache (Default):

fetch('https://api.example.com/data', { cache: 'force-cache' })

No Store (Dynamic):

fetch('https://api.example.com/data', { cache: 'no-store' })

Revalidate:

fetch('https://api.example.com/data', {
  next: { revalidate: 3600 } // Seconds
})

Tag-based Revalidation:

fetch('https://api.example.com/data', {
  next: { tags: ['posts'] }
})

// Revalidate elsewhere:
import { revalidateTag } from 'next/cache'
revalidateTag('posts')

Parallel Data Fetching

async function getData() {
  const [posts, users] = await Promise.all([
    fetch('https://api.example.com/posts').then(r => r.json()),
    fetch('https://api.example.com/users').then(r => r.json()),
  ])

  return { posts, users }
}

Sequential Data Fetching

async function getData() {
  const post = await fetch(`https://api.example.com/posts/${id}`).then(r => r.json())
  const author = await fetch(`https://api.example.com/users/${post.authorId}`).then(r => r.json())

  return { post, author }
}

Route Handlers (API Routes)

Basic Route Handler

// app/api/hello/route.ts
export async function GET(request: Request) {
  return Response.json({ message: 'Hello' })
}

export async function POST(request: Request) {
  const body = await request.json()
  return Response.json({ received: body })
}

Dynamic Route Handler

// app/api/posts/[id]/route.ts
export async function GET(
  request: Request,
  { params }: { params: { id: string } }
) {
  const post = await getPost(params.id)
  return Response.json(post)
}

export async function DELETE(
  request: Request,
  { params }: { params: { id: string } }
) {
  await deletePost(params.id)
  return new Response(null, { status: 204 })
}

Request Helpers

export async function GET(request: Request) {
  const { searchParams } = new URL(request.url)
  const id = searchParams.get('id')

  const cookies = request.headers.get('cookie')

  return Response.json({ id })
}

Response Types

// JSON
return Response.json({ data: 'value' })

// Text
return new Response('Hello', { headers: { 'Content-Type': 'text/plain' } })

// Redirect
return Response.redirect('https://example.com')

// Status codes
return new Response('Not Found', { status: 404 })

Navigation

Link Component

import Link from 'next/link'

export default function Page() {
  return (
    <>
      <Link href="/about">About</Link>
      <Link href="/blog/post-1">Post 1</Link>
      <Link href={{ pathname: '/blog/[slug]', query: { slug: 'post-1' } }}>
        Post 1 (alternative)
      </Link>
    </>
  )
}

useRouter Hook (Client)

'use client'

import { useRouter } from 'next/navigation'

export function NavigateButton() {
  const router = useRouter()

  return (
    <button onClick={() => router.push('/dashboard')}>
      Dashboard
    </button>
  )
}

Router Methods:

router.push(href) - Navigate to route
router.replace(href) - Replace current history
router.refresh() - Refresh current route
router.back() - Navigate back
router.forward() - Navigate forward
router.prefetch(href) - Prefetch route

Programmatic Navigation (Server)

import { redirect } from 'next/navigation'

export default async function Page() {
  const session = await getSession()

  if (!session) {
    redirect('/login')
  }

  return <div>Protected content</div>
}

Metadata & SEO

Static Metadata

// app/page.tsx
import { Metadata } from 'next'

export const metadata: Metadata = {
  title: 'My Page',
  description: 'Page description',
  keywords: ['nextjs', 'react'],
  openGraph: {
    title: 'My Page',
    description: 'Page description',
    images: ['/og-image.jpg'],
  },
  twitter: {
    card: 'summary_large_image',
    title: 'My Page',
    description: 'Page description',
    images: ['/twitter-image.jpg'],
  },
}

export default function Page() {
  return <div>Content</div>
}

Dynamic Metadata

// app/blog/[slug]/page.tsx
export async function generateMetadata({ params }): Promise<Metadata> {
  const post = await getPost(params.slug)

  return {
    title: post.title,
    description: post.excerpt,
    openGraph: {
      title: post.title,
      description: post.excerpt,
      images: [post.coverImage],
    },
  }
}

Metadata Files

favicon.ico, icon.png, apple-icon.png - Favicons
opengraph-image.png, twitter-image.png - Social images
robots.txt - Robots file
sitemap.xml - Sitemap

Image Optimization

Image Component

import Image from 'next/image'

export default function Page() {
  return (
    <>
      {/* Local image */}
      <Image
        src="/profile.png"
        alt="Profile"
        width={500}
        height={500}
      />

      {/* Remote image */}
      <Image
        src="https://example.com/image.jpg"
        alt="Remote"
        width={500}
        height={500}
      />

      {/* Responsive fill */}
      <div style={{ position: 'relative', width: '100%', height: '400px' }}>
        <Image
          src="/hero.jpg"
          alt="Hero"
          fill
          style={{ objectFit: 'cover' }}
        />
      </div>

      {/* Priority loading */}
      <Image
        src="/hero.jpg"
        alt="Hero"
        width={1200}
        height={600}
        priority
      />
    </>
  )
}

Image Props:

src - Image path (local or URL)
alt - Alt text (required)
width, height - Dimensions (required unless fill)
fill - Fill parent container
sizes - Responsive sizes
quality - 1-100 (default 75)
priority - Preload image
placeholder - 'blur' | 'empty'
blurDataURL - Data URL for blur

Remote Image Configuration

// next.config.js
module.exports = {
  images: {
    remotePatterns: [
      {
        protocol: 'https',
        hostname: 'example.com',
        pathname: '/images/**',
      },
    ],
  },
}

Font Optimization

Google Fonts

// app/layout.tsx
import { Inter, Roboto_Mono } from 'next/font/google'

const inter = Inter({
  subsets: ['latin'],
  display: 'swap',
})

const robotoMono = Roboto_Mono({
  subsets: ['latin'],
  display: 'swap',
  variable: '--font-roboto-mono',
})

export default function RootLayout({ children }) {
  return (
    <html lang="en" className={`${inter.className} ${robotoMono.variable}`}>
      <body>{children}</body>
    </html>
  )
}

Local Fonts

import localFont from 'next/font/local'

const myFont = localFont({
  src: './fonts/my-font.woff2',
  display: 'swap',
  variable: '--font-my-font',
})

Loading States

Loading File

// app/dashboard/loading.tsx
export default function Loading() {
  return <div>Loading dashboard...</div>
}

Streaming with Suspense

// app/page.tsx
import { Suspense } from 'react'

async function Posts() {
  const posts = await getPosts()
  return <ul>{posts.map(p => <li key={p.id}>{p.title}</li>)}</ul>
}

export default function Page() {
  return (
    <div>
      <h1>My Posts</h1>
      <Suspense fallback={<div>Loading posts...</div>}>
        <Posts />
      </Suspense>
    </div>
  )
}

Error Handling

Error File

// app/error.tsx
'use client'

export default function Error({
  error,
  reset,
}: {
  error: Error & { digest?: string }
  reset: () => void
}) {
  return (
    <div>
      <h2>Something went wrong!</h2>
      <p>{error.message}</p>
      <button onClick={() => reset()}>Try again</button>
    </div>
  )
}

Global Error

// app/global-error.tsx
'use client'

export default function GlobalError({
  error,
  reset,
}: {
  error: Error & { digest?: string }
  reset: () => void
}) {
  return (
    <html>
      <body>
        <h2>Something went wrong!</h2>
        <button onClick={() => reset()}>Try again</button>
      </body>
    </html>
  )
}

Not Found

// app/not-found.tsx
export default function NotFound() {
  return (
    <div>
      <h2>404 - Not Found</h2>
      <p>Could not find requested resource</p>
    </div>
  )
}

// Trigger programmatically
import { notFound } from 'next/navigation'

export default async function Page({ params }) {
  const post = await getPost(params.id)

  if (!post) {
    notFound()
  }

  return <div>{post.title}</div>
}

Middleware

// middleware.ts
import { NextResponse } from 'next/server'
import type { NextRequest } from 'next/server'

export function middleware(request: NextRequest) {
  // Authentication check
  const token = request.cookies.get('token')

  if (!token) {
    return NextResponse.redirect(new URL('/login', request.url))
  }

  // Add custom header
  const response = NextResponse.next()
  response.headers.set('x-custom-header', 'value')

  return response
}

export const config = {
  matcher: ['/dashboard/:path*', '/api/:path*'],
}

Environment Variables

# .env.local
DATABASE_URL=postgresql://...
NEXT_PUBLIC_API_URL=https://api.example.com

// Server-side only
const dbUrl = process.env.DATABASE_URL

// Client and server (NEXT_PUBLIC_ prefix)
const apiUrl = process.env.NEXT_PUBLIC_API_URL

Configuration

next.config.js

/** @type {import('next').NextConfig} */
const nextConfig = {
  // React strict mode
  reactStrictMode: true,

  // Image domains
  images: {
    remotePatterns: [
      { protocol: 'https', hostname: 'example.com' },
    ],
  },

  // Redirects
  async redirects() {
    return [
      {
        source: '/old-page',
        destination: '/new-page',
        permanent: true,
      },
    ]
  },

  // Rewrites
  async rewrites() {
    return [
      {
        source: '/api/:path*',
        destination: 'https://api.example.com/:path*',
      },
    ]
  },

  // Headers
  async headers() {
    return [
      {
        source: '/(.*)',
        headers: [
          { key: 'X-Frame-Options', value: 'DENY' },
        ],
      },
    ]
  },

  // Environment variables
  env: {
    CUSTOM_KEY: 'value',
  },
}

module.exports = nextConfig

Best Practices

Use Server Components: Default to Server Components, use Client Components only when needed
Optimize Images: Always use next/image for automatic optimization
Metadata: Set proper metadata for SEO
Loading States: Provide loading UI with Suspense
Error Handling: Implement error boundaries
Route Handlers: Use for API endpoints instead of separate backend
Caching: Leverage built-in caching strategies
Layouts: Use nested layouts to share UI
TypeScript: Enable TypeScript for type safety
Performance: Use priority for above-fold images, lazy load below-fold

Common Patterns

Protected Routes

// app/dashboard/layout.tsx
import { redirect } from 'next/navigation'
import { getSession } from '@/lib/auth'

export default async function DashboardLayout({ children }) {
  const session = await getSession()

  if (!session) {
    redirect('/login')
  }

  return <>{children}</>
}

Data Mutations (Server Actions)

// app/actions.ts
'use server'

import { revalidatePath } from 'next/cache'

export async function createPost(formData: FormData) {
  const title = formData.get('title')

  await db.post.create({ data: { title } })

  revalidatePath('/posts')
}

// app/posts/new/page.tsx
import { createPost } from '@/app/actions'

export default function NewPost() {
  return (
    <form action={createPost}>
      <input name="title" type="text" required />
      <button type="submit">Create</button>
    </form>
  )
}

Static Generation

// Generate static params for dynamic routes
export async function generateStaticParams() {
  const posts = await getPosts()

  return posts.map(post => ({
    slug: post.slug,
  }))
}

export default async function Post({ params }) {
  const post = await getPost(params.slug)
  return <article>{post.content}</article>
}

Deployment

Vercel (Recommended)

# Install Vercel CLI
npm i -g vercel

# Deploy
vercel

Self-Hosting

# Build
npm run build

# Start production server
npm start

Requirements:

Node.js 18.17 or later
output: 'standalone' in next.config.js (optional, reduces size)

Docker

FROM node:18-alpine AS base

FROM base AS deps
WORKDIR /app
COPY package*.json ./
RUN npm ci

FROM base AS builder
WORKDIR /app
COPY --from=deps /app/node_modules ./node_modules
COPY . .
RUN npm run build

FROM base AS runner
WORKDIR /app
ENV NODE_ENV production
COPY --from=builder /app/public ./public
COPY --from=builder /app/.next/standalone ./
COPY --from=builder /app/.next/static ./.next/static

EXPOSE 3000
CMD ["node", "server.js"]

Troubleshooting

Common Issues

Hydration errors
- Ensure server and client render same content
- Check for browser-only code in Server Components
- Verify no conditional rendering based on browser APIs
Images not loading
- Add remote domains to next.config.js
- Check image paths (use leading / for public)
- Verify width/height provided
API route 404
- Check file is named route.ts/js not index.ts
- Verify export named GET/POST not default export
- Ensure in app/api/ directory
"use client" errors
- Add 'use client' to components using hooks
- Import Client Components in Server Components, not vice versa
- Check event handlers have 'use client'
Metadata not updating
- Clear browser cache
- Check metadata export is named correctly
- Verify async generateMetadata returns Promise

Resources

Documentation: https://nextjs.org/docs
Learn Course: https://nextjs.org/learn
Examples: https://github.com/vercel/next.js/tree/canary/examples
Blog: https://nextjs.org/blog
GitHub: https://github.com/vercel/next.js

Implementation Checklist

When building with Next.js:

Repository: einverne/dotfiles
Path: claude/skills/nextjs/SKILL.md
Commit: b1b2fe0

Last updated: about 11 hours ago
First committed: 8 months ago

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