gistfile1.txt

function servePhoto(request) {
  var storageUrl = request.url.replace(/-\d+px\.jpg$/, '');

  return caches.open(contentImgsCache).then(function(cache) {
    return cache.match(storageUrl).then(function(response) {
      if (response) return response;

      return fetch(request).then(function(networkResponse) {
        cache.put(storageUrl, networkResponse.clone());
        return networkResponse;
      });
    });
  });
}