PushManager

PushManager is a browser API that manages push subscriptions for a Service Worker. It is exposed on a ServiceWorkerRegistration object as pushManager and provides methods to subscribe for push messages, retrieve an existing subscription, or manage the lifecycle of a subscription. Subscriptions created through PushManager enable servers to deliver notifications to users via the Web Push protocol.

The primary method is subscribe(options), which returns a Promise that resolves to a PushSubscription. The options typically include userVisibleOnly (a boolean indicating that every push message will result in a visible notification, usually required to be true) and applicationServerKey (the VAPID public key used to authenticate the server sending the push). Subscribing generally requires the user’s gesture and the site to be served over HTTPS (localhost is typically allowed for development). The resulting PushSubscription contains an endpoint URL and cryptographic keys that the server uses to address and encrypt messages.

The another method, getSubscription(), returns a Promise that resolves to the current PushSubscription or null if there isn’t one. This allows sites to check whether a user is already subscribed without attempting a new subscription.

PushManager also enables unsubscribing via the PushSubscription object, by calling unsubscribe(), which returns a Promise that resolves to a boolean indicating success.

In practice, the server uses the endpoint and keys from the PushSubscription to send messages to the user’s device through a push service. Subscriptions are tied to the user’s browser and device, and may require user permission again if revoked. PushManager support varies among browsers and platforms, and relies on service workers and secure contexts.