window.ShowModalDialog Vs window.Open retuning value

Var result = window.showModalDialog(url, window, 'dialogTop:200;dialogLeft:300;dialogHeight:' + windowHeight + 'px;dialogWidth:590px;resizable:0;'); -->i have OK,Cancel button's in child window.on click of OK button i am returning some values using below logic
string responseString = "<script language='javascript'> window.returnValue = \"" + OPCBrowserControl1.CurrentNodeId + "\" ;window.setTimeout('window.close()',100); </script>"; Response.Write(responseString);
i replaced the above code with Var result = window.open(url,"width:590,height:600");--->but here result variable contains window object,not the value i am returning on click of OK button.

How to rewrite the logic in window.open-->ok click event to achieve the result.