navigation Preload example workbox

addEventListener("fetch", event =>
    event.request.mode === "navigate" &&
    new URL(event.request.url, location.origin).pathname !== "/test" &&
    event.respondWith(event.preloadResponse)
);

// these are the routes we want to cache (i.e. no navigation preload will be necessary for these)
const routes = getRoutes(shells, paths);

// we enable
 navigationPreload.enable();

// we set up a navigation route catching all paths apart from the routes we are caching
 const navigationRoute = new routing.NavigationRoute(new strategies.NetworkOnly(), {
          blacklist: routes.map(route => {
                return new RegExp(`/${language}-${country}/${route.path}`);
          })
 });

routing.registerRoute(navigationRoute);

// we register the routes we want to cache using StaleWhileRevalidate strategy
for (let i = 0; i < routes.length; i++) {
        const staleWhileRevalidate = new strategies.StaleWhileRevalidate({ cacheName: routes[i].id });

        const shellRegEx = `/${language}-${country}/${routes[i].shell}`;
        const pathRegEx = new RegExp(`/${language}-${country}/${routes[i].path}`);

         routing.registerRoute(pathRegEx, () => {
                return staleWhileRevalidate.handle({ request: shellRegEx });
         });
}

// this is where we tried following the advice from @astrinxit66 i.e. we'll handle the preload response for these whitelisted navigation routes by using a CacheFirst strategy (since we cache these using the StaleWhileRevalidate strategy above)
const navigationRouteForShells = new routing.NavigationRoute(new strategies.CacheFirst(), {
         whitelist: routes.map(route => {
                return new RegExp(`/${language}-${country}/${route.path}`);
         })
});

routing.registerRoute(navigationRouteForShells);

self.addEventListener('activate', (event) => {
  if (self.registration && self.registration.navigationPreload) {
    event.waitUntil(
      self.registration.navigationPreload.enable().then(() => {
        // Defaults to Service-Worker-Navigation-Preload: true if not set.
        if (headerValue) {
          self.registration.navigationPreload.setHeaderValue(headerValue);
        }
      })
    );
  }
});