let client;

self.addEventListener('install', function(event) {
    self.skipWaiting();
});

self.addEventListener('activate', function(event){
    event.waitUntil(clients.claim());
    client = clients.matchAll().then(x => client = x[0]);
});

self.addEventListener('notificationclick', function(event) {
    event.notification.close();
    client.postMessage(event.notification.data);
});