JavaScript Confirm Box Server Side perform operation on OK and Cancel in ASP.Net

Hi All

I need to dispay confirm box on server Side.. senario is like Im Trying To upload Image During Upload Im Checking some properties like Image type,image size, etc.. While Uploading i want to check properties like

if(type=="xxxx")

{

confirmbox("  ");

if(confirmvalue=="yes")

{

next condition

}

else

{

exit ;

}

}

like this i want check different properies of file.. how can i do this