function ShowMsg(Msg,width,height)
{
window.showModelessDialog("javascript:alert(\""+Msg+"\");window.close();","","status:no;resizable:no;help:no;dialogHeight:"+height+"px;dialogWidth:"+width+"px;");
}
<script language="JavaScript">
var i=0;
function test()
{
window.showModelessDialog("javascript:alert();window.close();","","status:no;resizable:no;help:no;dialogHeight:30px;dialogWidth:40px;");
window.setInterval("aaaa.value=i++;",100);