add service worker and push notifications

static/sw.js

@@ -0,0 +1,32 @@
+/* eslint-env serviceworker */
+self.addEventListener('push', function (event) {
+  if (event.data) {
+    const data = event.data.json()
+
+    const promiseChain = clients.matchAll({
+      includeUncontrolled: true
+    }).then(function (clientList) {
+      const list = clientList.filter((item) => item.type === 'window')
+      if (list.length) return
+      return self.registration.showNotification(data.title, data)
+    })
+
+    event.waitUntil(promiseChain)
+  }
+})
+
+self.addEventListener('notificationclick', function (event) {
+  event.notification.close()
+
+  event.waitUntil(clients.matchAll({
+    includeUncontrolled: true
+  }).then(function (clientList) {
+    const list = clientList.filter((item) => item.type === 'window')
+
+    for (var i = 0; i < list.length; i++) {
+      var client = list[i]
+      if (client.url === '/' && 'focus' in client) { return client.focus() }
+    }
+    if (clients.openWindow) { return clients.openWindow('/') }
+  }))
+})