Service Worker

/*
// Source: https://madebymike.com.au//writing/service-workers/
<script>
  if ( 'serviceWorker' in navigator && ( typeof Cache !== 'undefined' && Cache.prototype.addAll ) ) {
    navigator.serviceWorker.register( '/sw.js' );
  }
</script>

*/

// we'll version our cache (and learn how to delete caches in
// some other post)
const cacheName = 'v1::static';

self.addEventListener('install', e => {
  // once the SW is installed, go ahead and fetch the resources
  // to make this work offline
  e.waitUntil(
    caches.open(cacheName).then(cache => {
      return cache.addAll([
        '/',
        /*
          DEAR READER,
          ADD A LIST OF YOUR ASSETS THAT
          YOU WANT TO WORK WHEN OFFLINE
          TO THIS ARRAY OF URLS
        */
      ]).then(() => self.skipWaiting());
    })
  );
});

// when the browser fetches a url, either response with
// the cached object or go ahead and fetch the actual url
self.addEventListener('fetch', event => {
  event.respondWith(
    caches.match(event.request).then(res => res || fetch(event.request))
  );
});