How to make a simple yes/no popup in ASP.NET that return the result back to my c#?

Question

With ASP.NET, how do I prompt the user for a yes/no question and getting the result back to my .ascx?

So far I can open a confirmation dialog with use of Javascript,

Answer 1

I use this. As far as I know it prevents the rest of the button event from executing.

btnMyButton.Attributes.Add("onClick", "return confirm('Are you really sure?')");