React & Next.js Guide 2026

React & Next.js Guide 2026 is the complete reference for building modern web applications with the most popular frontend stack. React is used by 40% of all web applications, and Next.js has become the standard way to build production React apps. This guide is updated for 2026 — React 18 and Next.js 14+ with App Router: - React 18 fundamentals and new features - Hooks: useState, useEffect, useContext, useReducer, and custom hooks - React Server Components: what they are and when to use them - Next.js App Router architecture - Server Actions for data mutations - Static and dynamic rendering strategies - Data fetching with fetch and React Query - Authentication with NextAuth.js v5 - Database integration: PostgreSQL with Prisma - Styling: Tailwind CSS and CSS Modules - Testing: Jest, React Testing Library, Playwright - Deployment: Vercel and self-hosted