[ken_ukeng]

Вариант 1:

$(function () {
  if ($(/*"ul.empty_legs_full_list_head"*/ul:first).offset(top:val.top/*0*/))
{
   $(".empty_legs_full_list_head")/*.append*//*.css*/.attr('position', 'fixed');,
}

 if($("ul:last").offset({top:0}))
 {
    $(".empty_legs_full_list_head").remove("position", "fixed").append("position", "static");
 }

Вариант 2:

function moveScroll() {
    var scroll = $(window).scrollTop();
    var table_top = $("#empty_legs_full_list_head").offset().top;
        clone_table = $("#clone");
        if (clone_table.length == 0) {
            clone_table = $("#empty_legs_full_list_head").clone();
            clone_table.attr('id', 'clone');
            clone_table.css({
                position: 'fixed',
                'pointer-events': 'none',
                top: 0
            });
            clone_table.width($("empty_legs_full_list_head").width() + vborder);
            $("#empty_legs_full_list_head").append(clone_table);
            $("#clone").css({
                visibility: 'visible'
            });
            $("#clone empty_legs_full_list").css({
                visibility: 'hidden'
            });
        }
    } else {
        $("#clone").remove();
    }
}
  $(window).scroll(moveScroll);