React: What is Next.js?

Next.js is a framework for React that adds server-side rendering (SSR), static generation (SSG), routing, and much more "out of the box".

Simple analogy: React is an engine (powerful, but you need to assemble the car yourself). Next.js is a ready-made car: sit down and drive. It already has:

• Steering wheel and pedals (routing by folders).
• Headlights and wipers (image optimization, SEO).
• GPS (Server Components, Server Actions).

What Next.js provides:

1. Routing — routing by file system: app/users/page.tsx = /users.
2. SSR (Server-Side Rendering) — HTML is generated on the server (fast loading, SEO).
3. SSG (Static Site Generation) — generation of static HTML files at build time.
4. ISR (Incremental Static Regeneration) — page regeneration on schedule (for example, once per hour).
5. Image Optimization — image optimization (WebP, lazy loading, resize).
6. Server Components — components on the server (React 19).
7. Server Actions — forms on the server without API.
8. Middleware — code that executes before the request (redirects, GeoIP, A/B tests).

Render types:

• Static (SSG) — build-time. Fast, but data is old.
• Dynamic (SSR) — request-time. Current, but slower.
• ISR — compromise: static, but with periodic updates.

React 19 + Next.js 15 — modern standard for React development.