How to Enable PreLoad Browser Hints with Service Workers
There are many subtle tricks to improve a site's page speed. One of the more advanced techniques is to use browser hints, which you can read about here.
One of these browser hints is 'preload', which causes the browser to start loading resources earlier than when they would normally be due to their position in the markup.
For example you can load scripts, images and other resources early. This does not mean the content will be processed, it just initiates the network request.
A problem might arise when using the preload hint and a service worker. The service worker must 'boot' before it handles network requests.
Read More About Enabling Navigation Preload in your Service Worker