React

React is Meta's library for building user interfaces from components. It is the default way a large share of product teams describe a screen: state in, UI out, a tree of pieces you can reuse. Instagram, Facebook, WhatsApp Web, and a long list of dashboards are React applications.

It is not a website by itself. You still need routing, data, and a build. Next.js, Remix, and Expo sit on top. React Native takes the same idea to phones. The centre is the component model, not the file extension.

Teams use React for web apps, design systems, and anything with enough interaction that a static template becomes a fight. Marketing sites use it when the CMS and the product share a system. Internal tools use it because hiring for React is easy.

We build in React when the interface has states, not only pages. We keep the tree small. We do not fetch the world to render a heading.

The interface layer for sites, SaaS, and tools.

Server Components where they help, client only where the interface must move. Types on every prop that matters. A tenth page is a CMS choosing order, not a new invention. The preview is the product you can refuse.

If a new view starts in a blank file, the system was not a system.