Handle network request to use cache storage

service-worker.js

self.addEventListener('fetch', event => {
  event.respondWith(
    caches.match(event.request).then(cacheResp => {
      return cacheResp || fetch(event.request).then(response => {
        return caches.open(CACHE_KEY).then(cache => {
          cache.put(event.request, response.clone())
          return response
        })
      })
    })
  )
})