The Push API allows a webapp to communicate with a user agent asynchronously. This allows an application server to provide the user agent with time-sensitive information whenever that information becomes known, rather than waiting for a user to open the webapp.
As defined here, push services support delivery of push messages at any time.
In particular, a push message will be delivered to the webapp even if that webapp is not currently active in a browser window: this relates to use cases in which the user may close the webapp, but still benefits from the webapp being able to be restarted when a push message is received. For example, a push message might be used to inform the user of an incoming WebRTC call.
A push message can also be sent when the user agent is temporarily offline. In support of this, the push service stores messages for the user agent until the user agent becomes available. This supports use cases where a webapp learns of changes that occur while a user is offline and ensures that the user agent can be provided with relevant information in a timely fashion. Push messages are stored by the push service until the user agent becomes reachable and the message can be delivered.
The Push API will also ensure reliable delivery of push messages while a user agent is actively using a webapp, for instance if a user is actively using the webapp or the webapp is in active communication with an application server through an active worker, frame, or background window. This is not the primary use case for the Push API. A webapp might choose to use the Push API for infrequent messages to avoid having to maintain constant communications with the application server.
Push messaging is best suited to occasions where there is not already an active communications channel established between user agent and webapp. Sending push messages requires considerably more resources when compared with more direct methods of communication such as fetch() or websockets. Push messages usually have higher latency than direct communications and they can also be subject to restrictions on use. Most push services limit the size and quantity of push messages that can be sent.
references:
https://www.w3.org/TR/push-api/
As defined here, push services support delivery of push messages at any time.
In particular, a push message will be delivered to the webapp even if that webapp is not currently active in a browser window: this relates to use cases in which the user may close the webapp, but still benefits from the webapp being able to be restarted when a push message is received. For example, a push message might be used to inform the user of an incoming WebRTC call.
A push message can also be sent when the user agent is temporarily offline. In support of this, the push service stores messages for the user agent until the user agent becomes available. This supports use cases where a webapp learns of changes that occur while a user is offline and ensures that the user agent can be provided with relevant information in a timely fashion. Push messages are stored by the push service until the user agent becomes reachable and the message can be delivered.
The Push API will also ensure reliable delivery of push messages while a user agent is actively using a webapp, for instance if a user is actively using the webapp or the webapp is in active communication with an application server through an active worker, frame, or background window. This is not the primary use case for the Push API. A webapp might choose to use the Push API for infrequent messages to avoid having to maintain constant communications with the application server.
Push messaging is best suited to occasions where there is not already an active communications channel established between user agent and webapp. Sending push messages requires considerably more resources when compared with more direct methods of communication such as fetch() or websockets. Push messages usually have higher latency than direct communications and they can also be subject to restrictions on use. Most push services limit the size and quantity of push messages that can be sent.
references:
https://www.w3.org/TR/push-api/
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