Div visible only after scrolling to specific waypoint

visible on scroll

var isVisible = false;
    $('#id').click(function(){
        $(window).scrollTop(0);
    });
    $(window).scroll(function(){
         var shouldBeVisible = $(window).scrollTop()>500;
         if (shouldBeVisible && !isVisible) {
              isVisible = true;
              $('#idr').show();
         } else if (isVisible && !shouldBeVisible) {
              isVisible = false;
              $('#id').hide();
        }
    });