In web push notification, it is important to build a subscriber base for sending push notifications. Users are prompted for permission to send push notifications when they land on the website. When users give their consent a unique subscriber id is generated. Web can then push notifications to all the subscribers. Web push notifications can be received on any devices with browsers like Chrome, Firefox and Safari.
For app notifications, user consent is usually taken at the time of app installation. This type of notification is restricted for mobile device only