Template page load script

page_load.js

/**
* Original Size:	855 bytes gzipped (2.33KB uncompressed)
* Compiled Size:	493 bytes gzipped (837 bytes uncompressed)
 * */

  // non-minified
  (function(window, document) {

      if (window.Promise) {

          var loader = '/compiled/assets/js/admin/loaders/editFooter/editFooterLoader.js';
          var polyfill = '/compiled/assets/js/vendor/polyfills.js';
          var scripts;
          var scriptLoaderBody;
          var scriptLoaderHead;
          var promise;

          scripts = [
              '/compiled/assets/js/vendor/require.js',
              '/compiled/assets/js/config/admin/config.js',
              loader
          ];

          scriptLoaderBody = function(scriptsX) {
              // appends scripts to the base of the document body
              script = document.createElement('script');
              script.src = scriptsX;
              script.type = 'text/javascript';
              document.body.appendChild(script);
          };

          scriptLoaderHead = function(scriptsX) {
              // appends scripts to the top of the document head
              var script;
              var stylesheet = document.querySelectorAll('[rel="stylesheet"]');
              var stylesheetLength = stylesheet.length - 1;

              script = document.createElement('script');
              script.src = scriptsX;
              script.type = 'text/javascript';
              stylesheet[stylesheetLength].parentNode.insertBefore(script, stylesheet[stylesheetLength]);

          };
          // uses promises to make sure that header and scripts are always
          // loaded in the right order
          promise = new Promise(function(resolve, reject) {

              var request = new XMLHttpRequest();
              // fetch header using AJAX
              request.open('GET', '/compiled/assets/js/admin/templates/common/header.html');
              request.onload = function() {

                  if (request.status === 200) {
                      resolve(request.response); // we got data here, so resolve the Promise
                  }

              };

              request.onerror = function() {
                  reject(Error('Error fetching data.')); // error occurred, reject the  Promise
              };

              request.send(); //send the request
          });

          promise.then(function(data) {
              // added contents of header template to the document.head
              document.head.insertAdjacentHTML('afterbegin', data);

          }).then(function() {

              scriptLoaderHead(polyfill);

          }).then(function() {

              // after head has been inserted then loaded then attach the three scripts to the bottom of the page
              var aSetInterval;

              scriptLoaderBody(scripts[0]);

              aSetInterval = setInterval(function() {
                  // Need to make sure that require is loaded first
                  if (typeof window.require === 'function') {
                      scriptLoaderBody(scripts[1]);
                      scriptLoaderBody(scripts[2]);
                      clearInterval(aSetInterval);
                  }

              }, 20);

          });

      } else {

          alert('Sorry, but this website does not work in your browser');

      }

  })(window, document);