Upgrading react-test-renderer 18 to 19

Makes flat config the default recommended preset and moves legacy config to recommended-legacy.

Fixes dev-only methods being exported in production builds; React.act is no longer available in production builds.

Removes support for using HTML comments (e.g. <!-- -->) as a DOM container.

Errors in render are no longer re-thrown; uncaught errors go to window.reportError and caught ones to console.error, customizable via onUncaughtError and onCaughtError.

propTypes is removed and silently ignored; migrate to TypeScript or another type-checking solution.

defaultProps is removed for function components; use ES6 default parameters instead. Class components still support defaultProps.

contextTypes and getChildContext are removed; legacy Context for class components is replaced by the contextType API.

String refs are removed; migrate any usage to ref callbacks.

Module pattern factories are removed; migrate to regular functions.

React.createFactory is removed; migrate all createFactory usage to JSX components.

ReactDOM.render and ReactDOM.hydrate are removed in favor of ReactDOM.createRoot and ReactDOM.hydrateRoot.

unmountComponentAtNode is removed in favor of root.unmount().

ReactDOM.findDOMNode is removed; replace it with DOM refs.

UMD builds are removed; load React 19 with an ESM-based CDN such as esm.sh when using a script tag.

Removes deprecated TypeScript types such as ReactChild, ReactFragment, ReactNodeArray, ReactText, VoidFunctionComponent and VFC.

Defaults ReactElement props to unknown instead of any for stricter typing.

Removes the global JSX namespace; JSX is now available from the React package.

Renames the react.element symbol to react.transitional.element.

Removes string refs.

Removes Legacy Context.

Removes RefreshRuntime.findAffectedHostInstances.

Removes client caching from the cache() API.

Removes propTypes.

Removes defaultProps support, except for classes.

Removes UMD builds.

Removes createFactory from React.

Removes render, hydrate, findDOMNode, unmountComponentAtNode, unstable_createEventHandle, unstable_renderSubtreeIntoContainer, and unstable_runWithPriority; moves createRoot and…

Removes unstable_flushControlled.

Removes legacy mode.

Removes renderToStaticNodeStream().

Removes unstable_renderSubtreeIntoContainer.

Renames the secret export of Client and Server internals.

Removes errorInfo.digest from onRecoverableError.

Removes prepareUpdate.

Removes isConcurrentMode and isAsyncMode methods.

Removes React internals access from useSyncExternalStore.

Updates useId to use valid CSS selectors, changing the format from :r123: to «r123».

The new JSX transform is now required, enabling ref as a prop and JSX speed improvements.

react-test-renderer/shallow is removed; use the third-party react-shallow-renderer package or testing libraries instead.

react-dom/test-utils is removed; act moved to react and all other utilities are removed.

Moves Requireable, ValidationMap, Validator and WeakValidationMap types to prop-types.

Moves ClassicComponentClass, ClassicComponent, ClassicElement, ComponentSpec, Mixin, ReactChildren, ReactHTML, ReactSVG and SFCFactory types to create-react-class.

Disallows implicit returns in refs; refs can accept cleanup functions and implicit returns of non-functions now error.

Requires the initial argument to useRef.

Makes ref objects returned from useRef always mutable.

Throws an error if react and react-dom versions do not match.

Replaces JavaScript URLs with functions that throw errors.

Removes test-utils.

Removes the react-test-renderer/shallow export.

Adjusts parameter order of createContainer and createHydrationContainer after on* handlers for upcoming experimental APIs.

Adds more DoS mitigations to Server Actions and hardens Server Components.

Adds extra loop protection to React Server Functions.

Requires Node.js 18 or newer.

Deprecates element.ref access in favor of element.props.ref, warning when accessed.

react-test-renderer logs a deprecation warning and switches to concurrent rendering for web usage.

Adds a deprecation error to react-test-renderer on web.