网页首页广告显示缓慢向上消失

    <div class="index_top">
        <!-- 顶部出现几秒后图片缓慢消失 -->
        <script language="javascript" type="text/javascript">
            window.onload = function () {

                var fudongAD = document.getElementById("headads");

                setTimeout("noneheadads()", 200); //停留时间自己适当调整


            }
            var height2 = 450; //高度
            function noneheadads() {
                height2 = height2 - 10;
                if (height2 <= 0) {
                    document.getElementById("headads").style.display = "none";
                    //                document.getElementById("toubiao").style.display = "block";
                    return;
                }
                document.getElementById("headads").style.height = height2 + "px";
                setTimeout("noneheadads()", 40);

            }

        </script>
        <div id="headads" style="margin: 0 auto; overflow: hidden;">
            <a href="http:///fmall/baihe/baihe.xhtml" target="_blank">
                <img src="http://static.baiinfo.com/p_w_picpath/20150722/20150722170115_5019.jpg" /></a></div>
        <div id="toubiao" style="display: none">
            <img src="@Url.Content("~/Content/Images/992_450.jpg")"  />
        </div>
    </div>