/* service worker */
{
  if ("serviceWorker" in navigator) {
    navigator.serviceWorker.register("/engine.js")
      .then((_reg) => {
        console.log("Registration successful");
      }).catch((error) => {
        console.log(`Registration error: ${error}`);
      });
  }

  self.addEventListener("install", function(event) {
    event.waitUntil(
      caches.open(CACHE_NAME)
      .then(function(cache) {
        console.log("Opened cache");
        return cache.addAll(urlsToCache);
      })
    );
  });
}