The applicationServerKey read-only property of the PushSubscriptionOptions interface contains the public key used by the push server.

A public key your push server uses to send messages to client apps via a push server. This value is part of a signing key pair generated by your application server, and usable with elliptic curve digital signature (ECDSA), over the P-256 curve. If no applicationServerKey member is passed when initialized, it will be set to null.

In the example below the value of applicationServerKey is printed to the console.

navigator.serviceWorker.ready.then((reg) => {
  reg.pushManager.getSubscription().then((subscription) => {
    const options = subscription.options;
    console.log(options.applicationServerKey); // the public key
  });
});