WordPress is upgrading from React 18 to React 19, shipping first in Gutenberg plugin version 23.3 and targeting WordPress 7.1. Plugin and theme developers need to migrate away from removed APIs: ReactDOM.render/hydrate (use createRoot/hydrateRoot), unmountComponentAtNode (use root.unmount()), findDOMNode (use refs), and defaultProps for function components (use ES6 defaults). Behavioral changes include the inert attribute becoming a boolean, ref callbacks now supporting cleanup function returns, and forwardRef being deprecated in favor of passing ref as a regular prop. New APIs available include use, useActionState, useOptimistic, useFormStatus, Activity, and useEffectEvent. TypeScript users face breaking changes: MutableRefObject is deprecated, ReactElement props changed from any to unknown, and HTML element prop naming conflicts may surface. Developers are encouraged to test with the Gutenberg plugin once React 19 is available and report issues on GitHub.
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