Pretty standard service worker reloading methodology we use

gistfile1.js

    if ('serviceWorker' in navigator) {
      var sitePath = '/';
      // discover this path downstream of the root of the domain
      var swScope = window.location.pathname.substring(0, window.location.pathname.indexOf(sitePath)) + sitePath;
      if (swScope != document.head.getElementsByTagName('base')[0].href) {
        document.head.getElementsByTagName('base')[0].href = swScope;
      }
      window.addEventListener('load', function () {
        navigator.serviceWorker.register('service-worker.js', {
          scope: swScope
        }).then(function (registration) {
          registration.onupdatefound = function () {
            // The updatefound event implies that registration.installing is set; see
            // https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#service-worker-container-updatefound-event
            var installingWorker = registration.installing;
            installingWorker.onstatechange = function () {
              switch (installingWorker.state) {
                case 'installed':
                  if (!navigator.serviceWorker.controller) {
                    window.dispatchEvent(new CustomEvent('simple-toast-show', {
                      bubbles: true,
                      cancelable: false,
                      detail: {
                        text: 'Pages you view are cached for offline use.',
                        duration: 8000
                      }
                    }));
                  }
                break;
                case 'redundant':
                  throw Error('The installing service worker became redundant.');
                break;
              }
            };
          };
        }).catch(function (e) {
          console.warn('Service worker registration failed:', e);
        });
        // Check to see if the service worker controlling the page at initial load
        // has become redundant, since this implies there's a new service worker with fresh content.
        if (navigator.serviceWorker.controller) {
          navigator.serviceWorker.controller.onstatechange = function(event) {
            if (event.target.state === 'redundant') {
              var b = document.createElement('paper-button');
              b.appendChild(document.createTextNode('Reload'));
              b.raised = true;
              b.addEventListener('click', function(e){ window.location.reload(true); });
              window.dispatchEvent(new CustomEvent('simple-toast-show', {
                bubbles: true,
                cancelable: false,
                detail: {
                  text: 'A site update is available. Reload for latest content.',
                  duration: 12000,
                  slot: b,
                  clone: false
                }
              }));
            }
          };
        }
      });
    }