Confirmation before executing CS Code

Hi .Net master and Guru
I want to execute a CS Code but before that, i want  a confirmation from user, it will be a javascript confirmation box, if the user say yes, then execute the code, or else leave cs code don't execute
below is my button code

<asp:Button  runat="server" ID="EmptyButton"  OnClick="EmptyButton_Click" OnClientClick="EmptyMyCart()" />
...