https://w3c.github.io/push-api/#pushmanager-interface says we should wait until the service worker registration has an active worker before creating a subscription, but we don't actually enforce that. It's possible to register a worker, capture its `PushManager`, unregister, and create subscriptions like so: let pushManager; navigator.serviceWorker.register("./sw.js").then(registration => { pushManager = registration.pushManager; return registration.unregister(); }).then(_ => { return pushManager.subscribe(); }).then(subscription => { // Created subscription without active worker. }); We should wait until the worker is active, and, once the registration is removed, `pushManager.subscribe()` should reject with an InvalidStateError.

Another issue is that a push subscription can be created by a non-active worker. See https://github.com/w3c/push-api/issues/221.