使用JAVASCRIPT实现弹出框，过一段时间自动消失

<script>
var oPopup;
var popTop=50;
var mytime;
function closemsg(){
try{
clearTimeout(mytime);
}catch(e){}
oPopup.hide();
}

function popshow(){
//window.status=popTop;
if(popTop>1160){
closemsg();
return;
}
if(popTop>1040&&popTop<1160){
oPopup.show(screen.width-195,screen.height,250,1160-popTop);
}
if(popTop>1000&&popTop<1040){
oPopup.show(screen.width-195,screen.height+(popTop-1160),250,116);
}
if(popTop<120){
oPopup.show(screen.width-195,screen.height,250,popTop);
}
if(popTop<160){
oPopup.show(screen.width-195,screen.height-popTop,250,116);
}
popTop+=10;
mytime=setTimeout("popshow();",100);
}

function popmsg(msgnum,msgstr){
oPopup = window.createPopup();
var winstr='<table style="border-top: #FFFFFF 1px solid; border-left: #FFFFFF 1px solid" cellSpacing=0 cellPadding=0 width="100%" bgcolor=#cfdef4 border=0>';
winstr +='<tr>';
winstr +='<td style="font-size: 12px; background-image: url(msgTopBg.gif); color: #0f2c8c" width=30 height=24></td>';
winstr +='<td style="font-weight: normal; font-size: 12px; background-image: url(msgTopBg.gif); color: #1f336b; padding-top: 4px;padding-left: 4px" valign=center width="100%"> 管理平台消息提示：</td>';
winstr +='<td style="background-image: url(msgTopBg.gif); padding-top: 2px;padding-right:2px" valign=center align=right width=19><span title=关闭 style="cursor: hand;color:red;font-size:12px;font-weight:bold;margin-right:4px;" onclick="window.parent.closemsg();">×</span></td>';
winstr +='</tr>';
winstr +='<tr>';
winstr +='<td style="padding-right: 1px; background-image: url(1msgBottomBg.jpg); padding-bottom: 1px" colSpan=3 height=90>';
winstr +='<div style="border-right: #b9c9ef 1px solid; padding-right: 13px; border-top: #728eb8 1px solid; padding-left: 13px; font-size: 12px; padding-bottom: 13px; border-left: #728eb8 1px solid; width: 100%; color: #1f336b; padding-top: 6px; border-bottom: #b9c9ef 1px solid; height: 100%">'
winstr +=' 您有<font color=#FF0000>'+msgnum+'</font>条新短消息<br><br>';
winstr +=' <div align=center style="word-break:break-all">';
winstr +=msgstr;
winstr +='</div>';
winstr +='</div>';
winstr +='</td>';
winstr +='</tr>';
winstr +='</table>';

oPopup.document.body.innerHTML = winstr;
popshow();
}
<!--上面是定议，下面是调用-->
popmsg(1,'msg');
</script>