WebPageTest preconnect/preload/... script

wpt-preconnect-preload-script.js

// Stolen from: https://andydavies.me/blog/2019/08/07/experimenting-with-link-rel-equals-preconnect-using-custom-script-injection-in-webpagetest/
(function () {
   var entries = [
       {'href': 'https://nav.files.bbci.co.uk', 'rel': 'preconnect'},
       {'href': 'https://nav.files.bbci.co.uk', 'rel': 'preconnect', 'crossOrigin': 'anonymous'}
   ];

   var fragment = document.createDocumentFragment();
   for(entry of entries) {
       var link = document.createElement('link');
       link.rel = entry.rel;
       link.href = entry.href;
       if(entry.hasOwnProperty('crossOrigin')) {
               link.crossOrigin = entry.crossOrigin;
       }
       if(entry.hasOwnProperty('as')) {
               link.as = entry.as;
       }
       fragment.appendChild(link);
   }
   document.head.appendChild(fragment);
   performance.mark('wpt.injectEnd'); // Not essential 
})();