offline support

Author: dwightjack

src/_includes/footer.njk

@@ -81,4 +81,8 @@
       }
     })
   }
+
+  if ('serviceWorker' in navigator) {
+    navigator.serviceWorker.register('/service-worker.js');
+  }
 </script>

static/service-worker.js

@@ -0,0 +1,32 @@
+/* eslint-disable no-undef */
+const cacheName = 'fevr-v2-cache';
+
+// import workbox
+importScripts(
+  'https://storage.googleapis.com/workbox-cdn/releases/5.1.2/workbox-sw.js',
+);
+const { routing, strategies } = workbox;
+
+const listRegExp = /^\/(index\.html|eventi\/index\.html)/;
+
+routing.registerRoute(
+  ({ url }) => !listRegExp.test(url.pathname),
+  new strategies.StaleWhileRevalidate({ cacheName }),
+);
+
+routing.registerRoute(
+  ({ url }) => listRegExp.test(url.pathname),
+  new strategies.NetworkFirst({ cacheName: cacheName + '-list' }),
+);
+
+// removes all caches not named <cacheName>
+const invalidateOldCache = async () => {
+  const keys = await caches.keys();
+  const isOldCache = (key) => !key.startsWith(cacheName);
+  const oldKeys = keys.filter(isOldCache);
+
+  return Promise.all(oldKeys.map((key) => caches.delete(key)));
+};
+
+// runs invalidateOldCache on activation
+self.addEventListener('activate', (e) => e.waitUntil(invalidateOldCache()));