Returns a boolean indicating whether the user's browser explicitly denies notifications. This happens if the user explicitly chooses to block notifications. Notifications may also be implicitly blocked if the allow/block notifications dialog is shown too many times without user interaction, the exact behavior is up to the browser.
If the function returns false the user must be instructed to enable notifications for the site since the web site can no longer prompt the user with the dialog.
Api.nativeNotificationsDenied();
See Api.nativeNotificationsSubscribe for example code.