Displays the same message even i use to change the message in script

Hello all,

I want the same thing as it is in MessageBox in asp.net i.e.
if dialog result =yes
// codeif dialog result ==no
//code


So i used :
 if (!ReturnValue())                         {
 string strconfirm = "<script>if(!window.confirm('Continue in demo mode?')){window.location.href='Default.aspx'}</script>";                             CSM.RegisterClientScriptBlock(this.GetType(), "Confirm", strconfirm, false);
}
bool ReturnValue()     {         return false;     }
< ...