sw.js

self.addEventListener('install', function(event){
  event.waitUntil(
    caches.open('NutPanda-cache-v10').then(function(cache){
       return cache.addAll([        // add the links to assests you want to cache
        'https://demo.com/main.css',
        'https://example.co/min.css',
        
       ]); 
    })
  );    
});

//This is the "Offline page" service worker
// make sure to create a page called offline.html
//Install stage sets up the offline page in the cache and opens a new cache
self.addEventListener('install', function(event) {
  var offlinePage = new Request('offline.html');
  event.waitUntil(
    fetch(offlinePage).then(function(response) {
      return caches.open('offline-v4').then(function(cache) {
        console.log(' Cached offline page during Install'+ response.url);
        return cache.put(offlinePage, response);
      });
  }));
});

//If any fetch fails, it will show the offline page.
//Maybe this should be limited to HTML documents?
self.addEventListener('fetch', function(event) {
  event.respondWith(
    fetch(event.request).catch(function(error) {
      console.error( 'Network request Failed. Serving offline page ' + error );
      return caches.open('offline-v4').then(function(cache) {
        return cache.match('offline.html');
      });
    }
  ));
});

//This is a event that can be fired from your page to tell the SW to update the offline page
self.addEventListener('refreshOffline', function(response) {
  return caches.open('offline-v4').then(function(cache) {
    console.log('Offline page updated from refreshOffline event: '+ response.url);
    return cache.put(offlinePage, response);
  });
});