Widget:ProjectLabel

<script> if(pageParams["page"]) new mw.Api().get({

   action: 'query',
   prop: 'revisions',
   rvprop: 'content',
   titles: pageParams["page"],
   format: 'json'

}).done(function (pageData) {

   var pageId = Object.keys(pageData.query.pages)[0];
   var content = pageData.query.pages[pageId].revisions[0]['*'];
   var pageUrl = mw.util.getUrl(page.title);

   const regex = /\[\[Category:(.*?)\]\]/gi;
   let categories = content.match(regex);
   console.log(categories);

}); </script>