How can i get the value that was pressed in the confirm box?
I just face similar problem in a real production project and I solved it by the following:
so the OnClientClick Client event is raised befoere the onClick which is a server event , so if the user clicks OK then the Client event returns True from the confirm Dialog and therefore the Code Behind this button is executed , on the other hand if the user clicks (Cancel or No) then it would return false and therefore the code behind wont get exected (Server Event is Cancelled)
hope it would help you as I really applied it to my project and worked without any issues.