service-worker.js

//code primarily from codelab
//Apache 2.0 licnense

const CACHE_NAME = 'static-cache-v1';

const FILES_TO_CACHE = [
    'index.html', 'source.js', 'style.css'
  ];

self.addEventListener('install', (evt) => {
  evt.waitUntil(
    caches.open(CACHE_NAME).then((cache) => {
      return cache.addAll(FILES_TO_CACHE);
    })
  );
  self.skipWaiting();
});

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

self.addEventListener('fetch', (evt) => {
  evt.respondWith(
      caches.open(DATA_CACHE_NAME).then((cache) => {
        return fetch(evt.request)
            .then((response) => {
              // If the response was good, clone it and store it in the cache.
              if (response.status === 200) {
                cache.put(evt.request.url, response.clone());
              }
              return response;
            }).catch((err) => {
              // Network request failed, try to get it from the cache.
              return cache.match(evt.request);
            });
      }));
  return;
});