Developer Guide to React 19: Async Handling

React 19 introduces several new hooks and APIs to simplify async handling, state management, and form submissions. The useTransition hook replaces manual isPending state variables by batching state updates into a single UI rerender. useActionState provides built-in form state and submission management, while useFormStatus lets child components access form properties without prop drilling. The new useOptimistic hook enables instant optimistic UI updates that auto-revert on error. The use API allows reading promises and context in render, including inside conditionals. Server Components let developers render HTML at build time or per-request on the server, reducing client-side bundle size. Server Actions enable client components to call async server functions via a 'use server' directive, creating a bidirectional client-server binding useful for form submissions and database operations.