WordPress is upgrading from ReactReact React is a JavaScript library that makes it easy to reason about, construct, and maintain stateless and stateful user interfaces. https://reactjs.org 18 to React 19. This change will first ship in the GutenbergGutenberg The Gutenberg project is the new Editor Interface for WordPress. The editor improves the process and experience of creating new content, making writing rich content much simpler. It uses ‘blocks’ to add richness rather than shortcodes, custom HTML etc. https://wordpress.org/gutenberg/ pluginPlugin A plugin is a piece of software containing a group of functions that can be added to a WordPress website. They can extend functionality or add new features to your WordPress websites. WordPress plugins are written in the PHP programming language and integrate seamlessly with WordPress. These can be free in the WordPress.org Plugin Directory https://wordpress.org/plugins/ or can be cost-based plugin from a third-party. (version 23.3) and is expected to land in WordPress 7.1.

In June 2024, WordPress 6.6 shipped React 18.3, which added deprecation warnings to help developers prepare for this upgrade (see Preparation for React 19 Upgrade). Now that the migrationMigration Moving the code, database and media files for a website site from one server to another. Most typically done when changing hosting companies. work is complete, this post covers everything plugin and theme developers need to know.

Timeline

• Gutenberg plugin: React 19 will be merged into the Gutenberg trunk branchbranch A directory in Subversion. WordPress uses branches to store the latest development code for each major release (3.9, 4.0, etc.). Branches are then updated with code for any minor releases of that branch. Sometimes, a major version of WordPress and its minor versions are collectively referred to as a "branch", such as "the 4.0 branch". after the 7.0 release. It will ship in a Gutenberg release shortly after, with npm packages following.
• WordPress CoreCore Core is the set of software required to run WordPress. The Core Development Team builds WordPress.: The upgrade is targeted for WordPress 7.1, providing a full release cycle for testing.

We encourage developers to begin testing as early as possible once the Gutenberg plugin release with React 19 is available.

Removed APIs

The following functions have been removed from React 19 after a long deprecation period. In WordPress, these were deprecated since WordPress 6.2 (March 2023):

render and hydrate

ReactDOM.render() and ReactDOM.hydrate() have been removed. Use createRoot() and hydrateRoot() instead:

// Before (deprecated).
import { render } from '@wordpress/element';
render( <App />, document.getElementById( 'root' ) );

// After.
import { createRoot } from '@wordpress/element';
const root = createRoot( document.getElementById( 'root' ) );
root.render( <App /> );

unmountComponentAtNode

ReactDOM.unmountComponentAtNode() has been removed. Use root.unmount() instead:

// Before (deprecated).
import { unmountComponentAtNode } from '@wordpress/element';
unmountComponentAtNode( document.getElementById( 'root' ) );

// After.
root.unmount();

findDOMNode

ReactDOM.findDOMNode() has been removed from React 19. However, @wordpress/element continues to export a polyfill for findDOMNode to ease the transition. Note that the react-dom script itself will no longer include this function — only the wp-element script will provide it.

We recommend migrating away from findDOMNode by using refs instead, as it was already discouraged in earlier versions of React.

defaultProps for function components

As noted in the React 18.3 dev note, defaultProps for function components is no longer supported. Use ES6 default parameters instead:

// Before (no longer supported).
function MyComponent( { size } ) {
	return <div style={ { width: size } } />;
}
MyComponent.defaultProps = { size: 100 };

// After.
function MyComponent( { size = 100 } ) {
	return <div style={ { width: size } } />;
}

Changed behavior

The inert attribute is now a boolean

The HTMLHTML HyperText Markup Language. The semantic scripting language primarily used for outputting content in web browsers. inert attribute has changed from a string type to a boolean in React 19. If your code sets inert as a string (inert="true" or inert=""), update it to use a boolean value:

// Before.
<div inert="" />
<div inert="true" />

// After.
<div inert />
<div inert={ true } />

Ref callbacks can return cleanup functions

Ref callbacks can now optionally return a cleanup function, similar to useEffect. React will call the cleanup function when the element is removed from the DOM. This is a powerful new pattern that reduces the need for separate useEffect hooksHooks In WordPress theme and development, hooks are functions that can be applied to an action or a Filter in WordPress. Actions are functions performed when a certain event occurs in WordPress. Filters allow you to modify certain functions. Arguments used to hook both filters and actions look the same. to manage DOM element lifecycle.

// New pattern: ref callback with cleanup.
<div ref={ ( node ) => {
	if ( node ) {
		const handler = () => { /* ... */ };
		node.addEventListener( 'scroll', handler );
		return () => node.removeEventListener( 'scroll', handler );
	}
} } />

Important: If your existing ref callbacks return a value (e.g., returning something other than undefined), React 19 may interpret that as a cleanup function. Make sure your ref callbacks either return undefined or a valid cleanup function.

forwardRef is no longer needed

In React 19, function components can accept ref as a regular prop. forwardRef still works but is considered deprecated and will be removed in a future version.

// Before.
const MyInput = forwardRef( ( props, ref ) => {
	return <input ref={ ref } { ...props } />;
} );

// After.
function MyInput( { ref, ...props } ) {
	return <input ref={ ref } { ...props } />;
}

New APIs available

React 19 introduces several new APIs, now available through @wordpress/element:

• use — Read a resource (Promise or Context) during render.
• useActionState — Manage state based on form action results.
• useOptimistic — Show optimistic UIUI User interface state while an async action is in progress.
• useFormStatus — Access the status of a parent form.

From React 19.2:

• Activity — Hide and show parts of the UI while preserving their state and DOM.
• useEffectEvent — Extract non-reactive logic from effects.

TypeScript type changes

React 19 includes a major update to its TypeScript types. Developers using TypeScript should be aware of the following:

Ref types

The MutableRefObject type is deprecated. The type inference rules for useRef and RefObject have changed, especially regarding declaring values as “T or null“. Update your code to use the new RefObject type.

ReactElement props type changed from any to unknown

The ReactElement type now types its props as unknown instead of any. This reveals previously unsound access to props that was silently allowed before. This manifests especially in cloneElement calls, where reading or setting props on a cloned element now requires the element type to explicitly support those props.

HTML element prop conflicts

Many WordPress components extend native HTML elements, accepting all props that (for example) a <div> accepts plus custom props. If the HTML standard adds a new prop to <div> with a name that conflicts with a custom prop, TypeScript may report errors. Developers may need to resolve naming conflicts (as was the case with onToggle in this migration).

For a comprehensive list of TypeScript changes, see the React 19 typechecking guide.

How to test your plugin

1. Install the latest Gutenberg plugin that includes React 19 (version TBD).
2. Enable development mode (SCRIPT_DEBUG set to true in wp-config.php) to get detailed warnings and errors.
3. Test all major features of your plugin — especially any code that uses the removed APIs (render, hydrate, unmountComponentAtNode, findDOMNode, defaultProps for function components).
4. Check the browser console for React warnings and errors. React 19 has improved error reporting and may surface issues that were previously silent.
5. Test iframeiframe iFrame is an acronym for an inline frame. An iFrame is used inside a webpage to load another HTML document and render it. This HTML document may also contain JavaScript and/or CSS which is loaded at the time when iframe tag is parsed by the user’s browser. interactions if your plugin renders content inside iframes or communicates between frames, as there have been subtle behavior changes in this area.

Further reading

• Official React 19 upgrade guide — Full list of breaking changes, deprecations, and new features.
• React 19 blog post — Overview of what’s new in React 19.
• Gutenberg tracking issue #71336 — Tracking the migration effort.
• Gutenberg PR #61521 — The main implementation PR.
• Preparation for React 19 Upgrade (WP 6.6 dev note) — The earlier dev notedev note Each important change in WordPress Core is documented in a developers note, (usually called dev note). Good dev notes generally include a description of the change, the decision that led to this change, and a description of how developers are supposed to work with that change. Dev notes are published on Make/Core blog during the beta phase of WordPress release cycle. Publishing dev notes is particularly important when plugin/theme authors and WordPress developers need to be aware of those changes.In general, all dev notes are compiled into a Field Guide at the beginning of the release candidate phase. from the React 18.3 upgrade.

Call for testing

We encourage all plugin and theme developers to test their code with the Gutenberg plugin as soon as the React 19 release is available. Early testing helps us identify and fix issues before the upgrade reaches WordPress Core. If you encounter bugs, please report them on the Gutenberg GitHub repository.

Props to @tyxla, @Mamaduka, @jsnajdr, @ellatrix, @aduth, @youknowriad, and @mciampini for their contributions to this migration.

#7-1, #dev-notes, #dev-notes-7-1