React 19

React 19 adds first-class support for asynchronous Actions, including useActionState, useFormStatus, and useOptimistic, so form submissions and other mutations can manage pending state, errors, and optimistic UI through React’s rendering model. It adds the use API for reading a Promise or context during render, and supports ref as a prop for function components, reducing the need for forwardRef in newly written components. React DOM gains built-in handling for document metadata, stylesheets, async scripts, and resource preloading. React 19 also improves hydration diagnostics, broadens custom-element support, and removes or deprecates several legacy APIs, including legacy ReactDOM rendering entry points and older testing utilities.

React 19 remains within its supported window, so there is no lifecycle-driven requirement to leave this major line immediately. The practical risk is instead version drift within the line and continued dependence on APIs that React 19 has removed or deprecated. Teams that postpone the React 19 migration from React 18 or earlier will miss the newer form and mutation patterns, improved hydration error reporting, and DOM resource handling, while carrying compatibility work for legacy rendering, ref, and test code. Teams already on React 19 should keep current supported updates applied; otherwise they may retain defects and interoperability issues already addressed in later releases on the same line.

Inventory the application’s React, React DOM, framework, test-renderer, and third-party component versions, then update them together to a current React 19-compatible set. Replace legacy ReactDOM.render and hydrate usage with createRoot and hydrateRoot, remove findDOMNode and string-ref dependencies, and review function components that rely on defaultProps or PropTypes behavior no longer provided by React. Update tests away from deprecated react-dom/test-utils APIs and treat react-test-renderer as a migration target where practical. Test hydration, forms, Suspense boundaries, custom elements, and any server-rendered paths in a production-like environment. Adopt Actions and the new form hooks selectively after the compatibility migration is stable, rather than combining broad application rewrites with the initial upgrade.