当没有元素出现在各自的方向时，禁用向上/向下箭头

Question

我在列表中有10个以上的图像，2个箭头图标可以向上和向下滚动以显示图像（就像旋转木马一样）。现在我想禁用向上/向下箭头，当列表中没有更多图像时，它是相应的方向。当下一个元素出现时，也启用这些箭头。

这是我的代码。

function favscroll(direction){
    var scrolltargetid= 'favorite-link-wrapper';
    var scrolltarget = document.getElementById(scrolltargetid);
    var scrolltargetheight= scrolltarget.scrollHeight;

    if(direction=='down'){
        $("#arrow-navup > a").removeClass('up');
        var targetposition = scrolltarget.scrollTop + scrolltarget.clientHeight;
        var distance=0;
        scrollintervall = setInterval (function () {
            $("#arrow-navdown").unbind("click");

            distance += 3;
            scrolltarget.scrollTop= scrolltarget.scrollTop + distance;
            if (  (scrolltarget.scrollTop >= (targetposition)) || ( scrolltarget.scrollTop >= scrolltarget.scrollHeight-scrolltarget.clientHeight) ){ 
                $("#arrow-navdown").bind("click", function(event) {
                    event.stopPropagation();
                    favscroll("down");
                    $("#arrow-navdown > a").addClass('down');
                });
                clearInterval (scrollintervall);
            }
        }, 20);
    }
    if(direction=='up'){
        $("#arrow-navdown > a").removeClass('down');
        var targetposition = scrolltarget.scrollTop - scrolltarget.clientHeight;
        var distance=0;
        scrollintervall = setInterval (function () {
            $("#arrow-navup").unbind("click");
            distance += 3;
            scrolltarget.scrollTop= scrolltarget.scrollTop - distance;
            if (  (scrolltarget.scrollTop <= (targetposition)) || ( scrolltarget.scrollTop <= 0) ){
                        $("#arrow-navup").bind("click", function(event) {
                        event.stopPropagation();
                        favscroll("up");
                        $("#arrow-navup > a").addClass('up');
                    });
                clearInterval (scrollintervall);
            }
        }, 20);
    }
}