An API that enables the browser to send “preload” network requests for navigations before executing the fetch event handler in the service worker that intercepts the target URL. The worker has access to the preload response inside the fetch event handler. Common use cases would be to respond with the preload response directly, or use it to populate the response.
Docs: https://developers.google.com/web/updates/2017/02/navigation-preload https://mattto.github.io/sw/demo/navigation-preload/ https://developer.mozilla.org/en-US/docs/Web/API/NavigationPreloadManager