Going Offline with Preact CLI

Preact CLI comes bundled with workbox. It takes advantage of InjectManifest plugin to gain and give high flexibility and more control over service worker use cases.

Preact CLI gives offline capabilities to the pre-built javascript/css and pre-rendered data out of the box.

Note: Preact CLI fetches navigation requests with Network first approach, meaning that you users will always see fresh content unless they are offline.

Custom functionality to your service worker

In order to make any changes to the default service worker functionality,

  • Create a sw.js file in src folder.
  • Paste the following snippet in this file to get the default functionality.
self.__precacheManifest = [].concat(self.__precacheManifest || []);

const isNav = event => event.request.mode === 'navigate';

 * Adding this before `precacheAndRoute` lets us handle all
 * the navigation requests even if they are in precache.
  ({ event }) => isNav(event),
  new workbox.strategies.NetworkFirst({
    // this cache is plunged with every new service worker deploy so we dont need to care about purging the cache.
    cacheName: workbox.core.cacheNames.precache,
    networkTimeoutSeconds: 5, // if u dont start getting headers within 5 sec fallback to cache.
    plugins: [
      new workbox.cacheableResponse.Plugin({
        statuses: [200], // only cache valid responses, not opaque responses e.g. wifi portal.

workbox.precaching.precacheAndRoute(self.__precacheManifest, {});

workbox.routing.setCatchHandler(({ event }) => {
  if (isNav(event))
    return caches.match(workbox.precaching.getCacheKeyForURL('/index.html'));
  return Response.error();
});Run in REPL
  • Make changes according to your needs

Adding other routes to runtime caching

If you want to add other routes or your API calls to runtime caching, follow the following steps.

  • Create a sw.js file in your src folder.
  • Add the following code with your respective settings.
  ({url, event}) => {
    return (url.pathname === '/special/url');
);Run in REPL
  • You can configure the above snippet with networkOnly to make sure that /special/url is never cached in service worker.

Note: Any custom routing code should be put before workbox.precaching.precacheAndRoute(self.__precacheManifest, precacheOptions);

Using other workbox modules in your service worker

Preact CLI imports worbox-sw in its service worker, thus all modules can be loaded on-demand as you use them. Feel free to use any module from workbox offering and it will be available on the global scope of service worker at runtime.

e.g.: Adding Background sync

Add the following code to the bottom of your sw.js.

const bgSyncPlugin = new workbox.backgroundSync.Plugin('myQueueName', {
  maxRetentionTime: 24 * 60 // Retry for max of 24 Hours (specified in minutes)

  new workbox.strategies.NetworkOnly({
    plugins: [bgSyncPlugin]
);Run in REPL