React 19 adds Actions for async forms, useActionState for managing form state, and useOptimistic for instant UI feedback. React Server Components run on the server with zero JavaScript sent to the browser.
React 19 New Features
- Actions — async form submissions without manual loading state
- useActionState — track async action results
- useOptimistic — optimistic UI updates
- use() — read context and promises in render
- Server Components — render on server, ship zero JS
// useOptimistic example
const [optimisticLikes, addOptimistic] = useOptimistic(likes);
async function likePosts() {
addOptimistic(optimisticLikes + 1);
await saveLike();
}