如何用window.open来实现window.showModalDialog的效果

var agent=window.navigator.userAgent;
var agentType=(agent.indexOf('MSIE')<1)?'FF':'IE';function showOpenWindow(url,objId,wTop,wLeft,wWidth,wHeight,isResize,isScroll,isReturn)
{
  var wFeatures;
  var wId=objId;
  
  if(agentType=='IE')
  {
    wFeatures=""
             +"dialogTop:"+wTop+"px;"
             +"dialogLeft:"+wLeft+"px;"
             +"dialogWidth:"+wWidth+"px;"
             +"dialogHeight:"+wHeight+"px;"
             +"resizable:"+isResize+";scroll:"+isScroll+";status:no;help:no";
  }
  else
  {
    wFeatures=""
             +"top="+wTop+","
             +"left="+wLeft+","
             +"width="+wWidth+","
             +"height="+(wHeight-30)+","
             +"dialog=yes,modal=yes,resizable="+isResize+",scrollbars="+isScroll+",status=no";
  }  if(agentType=='IE')
  {
    var getReturnValue=window.showModalDialog(url,wId,wFeatures);
    if(isReturn==1)
    {
      $(objId).value=getReturnValue;
    }
  }
  else
  {
    window.open(url,wId,wFeatures);
  }
}