react-19

useActionState takes an async function and initial state, returning [state, formAction, isPending]. Pass formAction to the form's action attribute, and return errors from the action instead of throwing them. Use useFormStatus in a child component for the submit button's pending state.

In React 19, ref is a regular prop, so remove the forwardRef wrapper and add ref to your props interface with type React.Ref<ElementType>. forwardRef still works but is deprecated and will be removed in a future version.

With React Compiler (React 19.1+), manual useMemo and useCallback are mostly obsolete because memoization happens automatically at build time. Only use them for computations over 100ms verified by profiling, stable references for effect dependencies, or third-party libraries requiring stable references.

Activity hides components while preserving their state, pausing effects instead of unmounting them. It is experimental (imported as experimental_Activity) and suits tabs, modals, and multi-step wizards where form inputs and state must survive visibility changes.

Use use() with Suspense for data fetching instead of useEffect, since use() can read promises directly in render and integrates with Suspense boundaries. useEffect remains appropriate for event listeners, timers, subscriptions, and DOM side effects that need cleanup.

useFormStatus must be called in a child component of the form, not in the component that renders the form itself. Extract your submit button into a separate child component and call useFormStatus there to access the pending state.