Custom error notification for user

[negativeten]

I'm looking for a way to utilize the 'popup' type notifications that are implemented within XF already to display custom messages to my users. Specifically, the types of error messages that are generated by the forum when an error is logged to the javascript console, or permission to view a forum is denied, etc.

I know there's a plugin on the market for this already, but I'd like to explore using what's already written before going that route. Can someone point me in the right direction to look?

Thanks!