Cache

var CACHE_VERSION = 1;

//       .
var CURRENT_CACHES = {
  font: "font-cache-v" + CACHE_VERSION,
};

self.addEventListener("activate", function (event) {
  var expectedCacheNames = Object.keys(CURRENT_CACHES).map(function (key) {
    return CURRENT_CACHES[key];
  });

  //       ,  promise   .
  event.waitUntil(
    caches.keys().then(function (cacheNames) {
      return Promise.all(
        cacheNames.map(function (cacheName) {
          if (expectedCacheNames.indexOf(cacheName) == -1) {
            console.log("Deleting out of date cache:", cacheName);

            return caches.delete(cacheName);
          }
        }),
      );
    }),
  );
});

self.addEventListener("fetch", function (event) {
  console.log("Handling fetch event for", event.request.url);

  event.respondWith(
    //   Cache,   'font'.
    caches.open(CURRENT_CACHES["font"]).then(function (cache) {
      return cache
        .match(event.request)
        .then(function (response) {
          if (response) {
            console.log("Found response in cache:", response);

            return response;
          }
        })
        .catch(function (error) {
          //    match()  fetch().
          console.error("Error in fetch handler:", error);

          throw error;
        });
    }),
  );
});