JS实现简单的顶部定时关闭层效果

<script type="text/javascript">
var time = 300;
var h = 0;
function addCount()
{
if(time>0)
{
time--;
h = h+5;
}
else
{
return;
}
if(h>300) //高度
{
return;
}
document.getElementById("ads").style.display = "";
document.getElementById("ads").style.height = h+"px";
setTimeout("addCount()",30);
}
window.onload = function showAds()
{
addCount();
setTimeout("noneAds()",7000); //停留时间自己调了
}
var T = 300;
var N = 300; //高度
function noneAds()
{
if(T>0)
{
T--;
N = N-5;
}
else
{
return;
}
if(N<0)
{
document.getElementById("ads").style.display = "none";
return;
}
document.getElementById("ads").style.height = N+"px";
setTimeout("noneAds()",30);
}
</script>