求助 js 代码

Question

一个设置透明度的函数，IE、FF都兼容.var alphanum=0;function setalpha(objid){
alphanum+=1;
obj=document.getElementById(objid);
if(navigator.appName=='Microsoft Internet Explorer'?true:false){
obj.style.filter='Alpha(opacity='+(alphanum*2.5)+')';
}else{
obj.style.opacity=alphanum/40;
}
if(alphanum<25){
alphatime=window.setTimeout('setalpha(\''+objid+'\')',20);
}else{
alphanum=0;
}
}