JavaScript PushManager getSubscription() Method

navigator.serviceWorker.ready.then((registration) => {
  registration.pushManager
    .getSubscription()
    .then((subscription) => {
      const pushButton = document.querySelector(".js-push-button");
      pushButton.disabled = false;

      if (!subscription) {
        // Not subscribed — keep Enable UI
        return;
      }

      // Keep server in sync + show Disable UI
      sendSubscriptionToServer(subscription);
      pushButton.textContent = "Disable Push Messages";
    })
    .catch((err) => {
      console.error(`Error during getSubscription(): ${err}`);
    });
});

async function checkPushSubscription() {
  const registration = await navigator.serviceWorker.ready;
  const subscription = await registration.pushManager.getSubscription();
  return subscription !== null;
}

const isSubscribed = await checkPushSubscription();
console.log(isSubscribed); // false until the user subscribes

const registration = await navigator.serviceWorker.ready;
const subscription = await registration.pushManager.getSubscription();

if (subscription) {
  console.log(subscription.endpoint);
  // e.g. "https://fcm.googleapis.com/fcm/send/…"
} else {
  console.log("No subscription — no endpoint");
}