push subscriptionchange upload token null

solution-1-upload-token-worker.ts

// To use IndexedDB like localStorage use this library.
// https://github.com/RyotaSugawara/serviceworker-storage
const storage = new ServiceWorkerStorage('sw:storage', 1);

async handlePush() {
  const newSubscription = await self.registration.pushManager.getSubscription();
  const oldSubscription = JSON.parse(await storage.getItem('subscription'));
  if(newSubscription.endpoint !== oldSubscription.endpoint) {
    storage.setItem('subscription', newSubscription);
    const req = new Request('/refreshpushsubscription', {
    method: 'POST',
    body: JSON.stringify(
        {oldSubscription: oldSubscription, newSubscription: newSubscription})
    });
    const response = await self.fetch(req);
  }

}

async savePush(subscription: PushSubscription) {
  await storage.setItem('subscription', subscription);
}

self.addEventListener('pushsubscriptionchange', (event: PushSubscriptionChangeEvent) => 
                      event.waitUntil(handlePush()));

// Listen messages from browser and wait for the first subscription to save it for
// future expirations.
self.addEventListener('message', (event) => {
  if(event.data.action === 'REQUEST_SUBSCRIPTION') {
     event.waitUntil(savePush(event.data.subscription));
  }
});