text: const version = '0.0.1';
  const cacheName = `drumkit-${version}`;
  
  self.addEventListener('install', event => {
    event.waitUntil(
      caches.open(cacheName).then(cache => {
        return cache.addAll([
          './',
          './index.html',
          './styles.css',
          './app.js',
          './soundfont-player.min.js',
          './hammer.min.js',
          './soundfonts.json',
          './site.webmanifest'
        ])
        .then(() => self.skipWaiting());
      })
    );
  });
  
  
  self.addEventListener('activate', event => {
    event.waitUntil(self.clients.claim());
  });
  
  self.addEventListener('fetch', event => {
    event.respondWith(
      caches.match(event.request).then(resp => {
        return resp || fetch(event.request).then(response => {
          return caches.open(cacheName).then(cache => {
            cache.put(event.request, response.clone());
            return response;
          });
        });
      })
    );
  });
  