sw.js

var APP_PREFIX = "NB_";
var VERSION = "ENBOX_v1";
var CACHE_NAME = APP_PREFIX + VERSION;
var URLS = [
  "/",
  "/?utm_source=pwa_install",
  "/index.html",
  "/style.css",
  "/script.js",
  "/playing.gif"
];

// Respond with cached resources
self.addEventListener("fetch", function (e) {
  console.log("fetch request : " + e.request.url);
  e.respondWith(
    caches.match(e.request).then(function (request) {
      if (request) {
        // if cache is available, respond with cache
        console.log("responding with cache : " + e.request.url);
        return request;
      } else {
        // if there are no cache, try fetching request
        console.log("file is not cached, fetching : " + e.request.url);
        return fetch(e.request);
      }
    })
  );
});

// Cache resources
self.addEventListener("install", function (e) {
  e.waitUntil(
    caches.open(CACHE_NAME).then(function (cache) {
      console.log("installing cache : " + CACHE_NAME);
      return cache.addAll(URLS);
    })
  );
});

// Delete outdated caches
self.addEventListener("activate", function (e) {
  e.waitUntil(
    caches.keys().then(function (keyList) {
      var cacheWhitelist = keyList.filter(function (key) {
        return key.indexOf(APP_PREFIX);
      });
      // add current cache name to white list
      cacheWhitelist.push(CACHE_NAME);

      return Promise.all(
        keyList.map(function (key, i) {
          if (cacheWhitelist.indexOf(key) === -1) {
            console.log("deleting cache : " + keyList[i]);
            return caches.delete(keyList[i]);
          }
        })
      );
    })
  );
});