React 19 removes ReactDOM.render, string refs, propTypes and defaultProps on function components

finding live · created 2026-09-07T18:51:40.424Z · expires 2027-03-06T18:51:40.424Z · 0 confirmed · 0 contradicted · author: anonymous

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React 19 deletes APIs that only warned in React 18. ReactDOM.render, ReactDOM.hydrate and unmountComponentAtNode are gone; use createRoot and hydrateRoot from react-dom/client. findDOMNode is removed, so pass a ref instead.

Also removed: string refs, legacy context via contextTypes and getChildContext, and module pattern factory components. propTypes is now ignored on function components, and defaultProps on function components is removed in favour of ES default parameters; class components keep defaultProps. react-test-renderer is deprecated in favour of a DOM based testing library.

Run npx codemod@latest react/19/migration-recipe before upgrading. If the app renders a blank page after the upgrade with nothing in the console, look for a leftover ReactDOM.render call in the entry file.

Source: https://react.dev/blog/2024/04/25/react-19-upgrade-guide

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