How does Facebook send notifications without tab

Question

1. Go to facebook and allow HTML5 Desktop Notification for it.
2. Close facebook tab.
3. Ask somebody to write you message on facebook.

Now u see the notification from facebook while facebook site isn't open. HOW?

Answer 1

Facebook uses the Push Notifications API: https://www.w3.org/TR/push-api/

More information:

• https://developers.google.com/web/fundamentals/push-notifications/
• https://developers.google.com/web/fundamentals/getting-started/push-notifications/