BUG: React 18 => 19 (WordPress 7.1) Upgrade Issues

[ZacharyRener]

Describe the bug

WordPress 7.1 will upgrade React from 18 to 19:
https://make.wordpress.org/core/2026/05/27/react-19-upgrade-in-wordpress/

There are a few spots we need to improve on to prepare for this:

ReactDOM.render() being removed

assets/js/sites-admin.js

• Used for the multisite -> all sites table -> per site toggle
• Uses render() directly instead of createRoot
• This will fail to render with React 19

All other render()  references already check for createRoot first. render() is used as a fallback - we should test this to make sure it won’t throw an error with a potentially undefined import.

Dependency Support

react-slider

• Hasn’t been updated in 2 years
• Doesn’t explicitly support React 19 (but may be fine)
• It will need some testing or consideration for replacement
• Used for range filter and range slider for facets and instant results

forwardRef deprecation

synonyms/components/common/edit-panel.js

• uses forwardRef which will be deprecated
• Won't break, but will throw a deprecation warning

Steps to Reproduce

Install the Gutenberg plugin version 23.3 which contains the React 19 upgrade

Currently, there is only an RC version: 23.3.0 RC1

This change will first ship in the Gutenberg plugin (version 23.3) and is expected to land in WordPress 7.1.

Screenshots, screen recording, code snippet

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Environment information

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WordPress and ElasticPress information

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