如何判断一个窗口是否打开再决定是否关闭呀?


<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
 <HEAD>
  <script language="javascript">
  var winobj=null;
    function simpleMove(){
        winobj=window.open("对象.html","win1","width=260,height=500,resizble=no,left=0,top=0");
        winobj.moveTo(0,0);
        winobj.focus();
        parent.window.moveTo(275,0);
        parent.window.resizeTo(480,430);
    }
    function closeWindow(){
        if(winobj!=null && !winobj.closed){ winobj.close(); winobj=null;}
    }
  </script>
 </HEAD> <BODY bgcolor="lightblue">
 <h2>新建窗口及原窗口的移动<h2>
 <br>
 <form>
    <input type="button" value="打开窗口" onClick="simpleMove();">
</form>
 <a href="javascript:closeWindow()">关闭新开的窗口</a></h3>
 </BODY>
</HTML>