scrollTop - not working

how to find scrollTop in jquery?
$(document).ready(function () {
    $("body").click(function () {
        alert($("body").scrollTop());
    });
});
the above code returns only 0.
It seems doctype is not supporting.
<!DOCTYPE html public "-//W3C//DTD Xhtml 1.0 Transitional//EN" "http://
www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">