FetchEvent.navigationPreload

The navigationPreload read-only property of the FetchEvent interface returns a Promise that resolves to the instance of NavigationPreloadManager associated with the current service worker registration.

var promise = fetchEvent.navigationPreload

A Promise that resolves to the instance of NavigationPreloadManager.

The following example shows the implementation of a fetch event that uses a preloaded response. 

addEventListener('fetch', event => {
  event.respondWith(async function() {
    // Respond from the cache if we can
    const cachedResponse = await caches.match(event.request);
    if (cachedResponse) return cachedResponse;

    // Else, use the preloaded response, if it's there
    const response = await event.preloadResponse;
    if (response) return response;

    // Else try the network.
    return fetch(event.request);
  }());
});