Note: After saving, you have to bypass your browser's cache to see the changes. Google Chrome, Firefox, Microsoft Edge and Safari: Hold down the ⇧ Shift key and click the Reload toolbar button. For details and instructions about other browsers, see Wikipedia:Bypass your cache.
mw.loader.load('//meta.wikimedia.org/w/index.php?title=User:FR30799386/undo.js&action=raw&ctype=text/javascript'); // [[:meta:User:FR30799386/undo.js]]