纯JS幻灯片广告代码实现

<script>
var widths=960;
var heights=221;
var counts=2;
img1=new Image ();img1.src='/cngcb/banner.jpg';
img2=new Image ();img2.src='/cngcb/banner2.jpg';
url1=new Image ();url1.src='#';
url2=new Image ();url2.src='#';
var nn=1;
var key=0;
function change_img()
{if(key==0){key=1;}
else if(document.all)
{document.getElementById("pic").filters[0].Apply();document.getElementById("pic").filters[0].Play(duration=2);}
eval('document.getElementById("pic").src=img'+nn+'.src');
eval('document.getElementById("url").href=url'+nn+'.src');
for (var i=1;i<=counts;i++){document.getElementById("xxjdjj"+i).className='axx';}
document.getElementById("xxjdjj"+nn).className='bxx';
nn++;if(nn>counts){nn=1;}
tt=setTimeout('change_img()',4000);}
function changeimg(n){nn=n;window.clearInterval(tt);change_img();}
document.write('<style>');
document.write('.axx{padding:1px 7px;border-left:#cccccc 1px solid;}');
document.write('a.axx:link,a.axx:visited{text-decoration:none;color:#fff;line-height:12px;font:9px sans-serif;background-color:#666;}');
document.write('a.axx:active,a.axx:hover{text-decoration:none;color:#fff;line-height:12px;font:9px sans-serif;background-color:#999;}');
document.write('.bxx{padding:1px 7px;border-left:#cccccc 1px solid;}');
document.write('a.bxx:link,a.bxx:visited{text-decoration:none;color:#fff;line-height:12px;font:9px sans-serif;background-color:#D34600;}');
document.write('a.bxx:active,a.bxx:hover{text-decoration:none;color:#fff;line-height:12px;font:9px sans-serif;background-color:#D34600;}');
document.write('</style>');
document.write('<div style="width:'+widths+'px;height:'+heights+'px;overflow:hidden;text-overflow:clip;">');