caching

Open Event Webapp Generator takes in the event data in form of a JSON zip or an API endpoint as input and outputs an event website. Since the generated event websites are static, we can use caching of static assets to improve the page-load time significantly. All this has been made possible by the introduction of service workers in the browsers. Service workers are event-driven scripts (written in JavaScript) that have access to domain-wide events, including network fetches.With the help of service workers, we can cache all static resources, which could drastically reduce network requests and improve performance considerably, too. The service workers are like a proxy which sits between the browser and the network and intercept it. We will listen for fetch events on these workers and whenever a request for a resource is made, we intercept and process it first. Since our generated event sites are static, it makes no sense to fetch the assets again and again. When a user first loads a page, the script gets activated and try to cache all the static assets it can. On further reload of the page, whenever the browser request for an already stored asset, instead of fetching it from the network, it can directly give them back to the browser from the local store. Also, in the meantime, it is also caching all the new static assets so they won't be loaded or fetched again from the network later. Thus the performance of the app gets increased more and more with every reload. It becomes fully functional offline after a few page loads. The issue for this feature is here and the whole work can be seen here. To know more details about the basic functioning and the lifecycle of the service workers, check out this excellent Google Developers article. This blog mainly focuses on how we added service workers in the event websites. We create a new fallback HTML page offline.html to return in response to an offline user who requests a page which has not been cached yet. Similarly, for images, we have a fallback image named avatar.png which is returned when the requested image is not present in the local store and the network is down. Since these assets are integral to the functioning of the service worker, we cache them in the installation step itself. The whole service worker file can be seen here var urlsToCache = [ './css/bootstrap.min.css', './offline.html', './images/avatar.png' ]; self.addEventListener('install', function(event) { event.waitUntil( caches.open(CACHE_NAME).then(function(cache) { return cache.addAll(urlsToCache); }) ); }); All the other assets are cached lazily. Only when they are requested, we fetch them from the network and store it in the local store. This way, we avoid caching a large number of assets at the install step. Caching of several files in the install step is not recommended since if any of the listed files fails to download and cache, then the service worker won’t be installed! self.addEventListener('fetch', function(event) { event.respondWith(caches.match(event.request).then(function(response) { // Cache hit - return response if (response) { return response; } // Fetch resource from internet and put…