Push API

La API Push otorga a las aplicaciones web la habilidad de recibir mensajes enviados a ellas desde un servidor, sin importar si la aplicación está o no en primer plano o cargada. Esto permite a los desarrolladores enviar notificaciones asíncronas y actualizaciones para los usuarios que las aceptan.

Push concepts and usage

For an app to receive push messages, it has to have an active service worker. When the service worker is active, it can subscribe to push notifications using PushManager.subscribe().

The resulting PushSubscription includes all the information that the application needs to send a push message: an endpoint and the encryption key needed for sending data.

The service worker will be started as necessary to handle incoming push messages, which are delivered to the ServiceWorkerGlobalScope.onpush event handler. This allows apps to react to push messages being received, for example by displaying a notification (using ServiceWorkerRegistration.showNotification().)

Each subscription is unique to a service worker.  The endpoint for the subscription is a unique capability URL: knowledge of the endpoint is all that is necessary to send a message to your application. The endpoint URL therefore needs to be kept secret, or other applications might be able to send push messages to your application.

Activating a service worker to deliver a push message can result in increased resource usage, particularly of the battery. Different browsers have different schemes for handling this — there is currently no standard mechanism. Firefox allows a limited number of push messages to be sent to an application.  This limit is refreshed each time that the site is visited. In comparison, Chrome applies no limit but requires that applications show a notification each time that a push message is received, which allows the user to confirm that they still want to receive notifications and ensures user visibility.

Interfaces

PushEvent

Represents a push action sent to the global scope of a ServiceWorker. It contains information sent from an application to a PushSubscription.

PushManager

Provides a way to receive notifications from third-party servers as well as request URLs for push notifications. This interface has replaced functionality offered by the obsolete PushRegistrationManager interface.

PushMessageData

Provides access to push data sent by a server, and includes methods to manipulate the received data.

PushSubscription

Provides a subcription's URL endpoint and allows unsubscription from a push service.

Service worker additions

The following additions to the Service Worker API have been specified in the Push API spec, to provide an entry point for using Push messages, and  to monitor and respond to push and subscription change events.

ServiceWorkerRegistration.pushManager Read only

Returns a reference to the PushManager interface for managing push subscriptions including subscribing, getting an active subscription, and accessing push permission status. This is the entry point into using Push messaging.

ServiceWorkerGlobalScope.onpush

An event handler fired whenever a push event occurs; that is, whenever a server push message is received.

ServiceWorkerGlobalScope.onpushsubscriptionchange

An event handler fired whenever a pushsubscriptionchange event occurs; for example, when a push subscription has been invalidated, or is about to be invalidated (e.g. when a push service sets an expiration time.)

Specifications

Browser Compatibility

[1] Currently available only on desktop versions of Firefox; also, push messages are only delivered when Firefox is running.

[2]: Microsoft Edge status: Under Consideration; Roadmap Priority: Low

See also

• Using the Push API
• Push API Demo, on Github
• Push Notifications on the Open Web, Matt Gaunt
• Service Worker API