What is React?

React is a declarative, component-based UI library built around a virtual DOM reconciliation algorithm.

Components are pure functions of their props and state: UI = f(state). React computes the next render, diffs it against the previous tree, and commits the minimal set of DOM mutations.

Rendering is synchronous by default but can be interrupted in concurrent mode (React 18+), enabling features like transitions and Suspense to keep the UI responsive under load.