Differentiate between "not allowed" and "denied"

[ehq]

Right now checking permissions (on browsers that support it) returns a kind of binary response, either "granted" or "denied": https://github.com/MrSwitch/notification.js/blob/master/notification.js#L97

The problem with that is that there are cases where it's useful to differentiate why notifications are not currently allowed.

• If the user still hasn't either allowed or denied desktop notifications, then I want to request permission to show them notifications.
• If the user refused allowing desktop notifications then I don't want to bother them by asking for permission again.

I think Notification.permission could return these possible values (just as an example):

• unknown
• enabled
• disabled
• denied

[MrSwitch]

Seems reasonable, open to Pull Request