script changes div to fixed position - convert jquery solution to mootools

Question

I need to have a div that is positioned in the middle of the screen on page load, and that scrolls with the rest of the screen, change to a fixed position when it hits the top of the screen. I found a solution for this written in jquery, but I need it in mootools. Can anyone help me with this?

function sticky_relocate() {
var window_top = $(window).scrollTop();
var div_top = $('#right-column').offset().top;
  if (window_top > div_top)
    $('#contact').addClass('fixed')
  else
    $('#contact').removeClass('fixed');
}
 $(function() {
$(window).scroll(sticky_relocate);
sticky_relocate();
});

Answer 1

function sticky_relocate() {
    var window_top = $(window).getScroll().y;
    var div_top = $('right-column').getPosition().y;

    if (window_top > div_top)
        $('contact').addClass('fixed')
    else
        $('contact').removeClass('fixed');
}

$(window).addEvent('scroll', function(){
    sticky_relocate();
});
sticky_relocate();