# React
Status: public
Confidence: medium (0.725) (verified)
Last verified: 2026-05-24
Generation: ai_structured


## TL;DR

React is an open-source JavaScript library for building user interfaces from reusable components. React 19 was announced as stable on December 5, 2024 and added new APIs around Actions, forms, optimistic updates, and Server Components integration.

## Core Concepts

- **Components**: reusable UI pieces that return markup.
- **JSX**: JavaScript syntax extension commonly used to describe component output.
- **Hooks**: functions for using React features from components.
- **Actions**: React 19 pattern for async transitions and form-related mutations.
- **Server Components**: components rendered in a separate server environment before bundling or per request.

## Further Reading

- [Your First Component](https://react.dev/learn/your-first-component)
- [React v19](https://react.dev/blog/2024/12/05/react-19)
- [Server Components](https://react.dev/reference/rsc/server-components)