font-defer-without-fallback

(function() {

   var files = ['assets/site/css/non-critical.css', 'assets/site/img/icons.svg'];
   
   function getExtension(src) {
      return src.split('.').pop();
   }

   function injectContent(content, type) {
      if (type === 'css') {
         var style = document.createElement('style');
         document.head.appendChild(style);
         if (style.styleSheet) {
            style.styleSheet.cssText = content;
         } else {
            style.innerHTML = content;
         }
      } else if (type === 'svg') {
         document.head.insertAdjacentHTML('beforeend', content);
      }
   }

   function loadFile(file) {
      var content = localStorage[file];
      if (content) {
         injectContent(content, getExtension(file));
      } else {
         window.addEventListener('load', function get() {
            var xhr = new XMLHttpRequest();
            xhr.open('GET', file, true);
            xhr.addEventListener('load', function() {
               if (xhr.readyState === 4) {
                  injectContent(xhr.responseText, getExtension(file));
                  localStorage[file] = xhr.responseText;
               }
            });
            xhr.send();
            window.removeEventListener('load', get);
         });
      }
   }

   if (window.localStorage) {
      files.forEach(function(file) {
         if (getExtension(file) === 'svg' && !document.implementation.hasFeature('http://www.w3.org/TR/SVG11/feature#Image', '1.1')) {
            return;
         }
         loadFile(file);
      });
   }

})();