javascript实现网站顶部出现几秒后图片缓慢消失的效果

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=gb2312" /> <title>脚本之家 www.gxlcms.com</title> <script language="javascript" type="text/javascript"> window.onload = function(){ var fudongAD = document.getElementById("headads"); setTimeout("noneheadads()", 3000); //停留时间自己适当调整 } var height2 = 339; //高度 function noneheadads() { height2 = height2 - 10; if (height2 <= 0) { document.getElementById("headads").style.display = "none"; return; } document.getElementById("headads").style.height = height2 + "px"; setTimeout("noneheadads()", 40); } </script> </head> <body> <img src="http://img.gxlcms.com//Uploads-s/new/2019-09-17-201917/2011012812333783.jpg" /> </body> </html>
[Ctrl+A 全选 注:如需引入外部Js需刷新才能执行]