sw.js

const CACHE_NAME          = 'com.thingsimplied.static.v1'
const DYNAMIC_CACHE_NAME  = 'com.thingsimplied.dynamic.v1'

const urlsToCache = [
  '/',
  '/favicon.ico',
  '/manifest.json',
];

self.addEventListener('install', function(event) {
  // Perform install steps
  event.waitUntil(
    caches.open(CACHE_NAME)
      .then(function(cache) {
        return cache.addAll(urlsToCache)
      })
  )
})

self.addEventListener('fetch', function(event) {
  event.respondWith(
    caches.match(event.request)
      .then(function(response) {
        if (response) {
          return response
        }

        // IMPORTANT: Clone the request. A request is a stream and
        // can only be consumed once. Since we are consuming this
        // once by cache and once by the browser for fetch, we need
        // to clone the response.
        var fetchRequest = event.request.clone();

        return fetch(fetchRequest).then(
          function(response) {
            // Check if we received a valid response
            if(!response || response.status !== 200 || response.type !== 'basic') {
              return response
            }

            // IMPORTANT: Clone the response. A response is a stream
            // and because we want the browser to consume the response
            // as well as the cache consuming the response, we need
            // to clone it so we have two streams.
            var responseToCache = response.clone()

            caches.open(DYNAMIC_CACHE_NAME)
              .then(function(cache) {
                cache.put(event.request, responseToCache)
              })

            return response;
          }
        )
      }
    )
  )
})

self.addEventListener('activate', function(event) {

  var cacheWhitelist = [CACHE_NAME, DYNAMIC_CACHE_NAME]

  event.waitUntil(
    caches.keys().then(function(cacheNames) {
      return Promise.all(
        cacheNames.map(function(cacheName) {
          if (cacheWhitelist.indexOf(cacheName) === -1) {
            return caches.delete(cacheName);
          }
        })
      )
    })
  )
})