service-worker-activate-fetch.js

self.addEventListener('activate', function(e) {
  e.waitUntil(caches.keys()
    .then(function(keyList) {
      return Promise.all(keyList.map(function(key) {
        if (key !== cacheName)
          return caches.delete(key);
      }));
  }));
  return self.clients.claim();
});

self.addEventListener('fetch', function(e) {
  e.respondWith(caches.match(e.request)
    .then(function(response) {
      return response || fetch(e.request)
        .then(function (resp){
          return caches.open(cacheName)
            .then(function(cache){
              cache.put(e.request, resp.clone());
              return resp;
          })
        }).catch(function(event){
          console.log('Error fetching data!');
        })
      })
  );
});