在Javascript 中实现window.open弹出窗口居中显示

<Script language="javascript" type="text/javascript">
function openwindow(url,name,iWidth,iHeight)
 {
  var url;                                 //转向网页的地址;
  var name;                           //网页名称，可为空;
  var iWidth;                          //弹出窗口的宽度;
  var iHeight;                        //弹出窗口的高度;
  var iTop = (window.screen.availHeight-30-iHeight)/2;       //获得窗口的垂直位置;
  var iLeft = (window.screen.availWidth-10-iWidth)/2;           //获得窗口的水平位置;
  window.open(url,name,'height='+iHeight+',,innerHeight='+iHeight+',width='+iWidth+',innerWidth='+iWidth+',top='+iTop+',left='+iLeft+',toolbar=no,menubar=no,scrollbars=auto,resizeable=no,location=no,status=no');
 }
</Script>