‘undefined’ Is Not an Object.
Of course, you are a better developer and can make things better in your own product. Technically you can always test your website with developers console open. But tiny icon in top-left corner is easy to miss.
If you are like me, and can not install extensions because of security reasons I can suggest a tiny, stripped-down alternative. The codebase is bare minimum and the extension runs only on localhost, to satisfy strict security requirements. The extension is intended to be installed from local disk.
Extension handles both handled and unhandled errors - so will work both with your regular pages and React.