showModalDialog in javascript

var value=window.showModalDialog("frmTrgDDOView.aspx","Null","dialogWidth:500px; dialogHeight:400px; scroll:no; center:yes");

         document.getElementById('<%=txtddocode.ClientID %>').value=value[0];
         document.getElementById('<%=txtddodesc.ClientID %>').value =value[1];


return value from popup window
----------------------------------
window.returnValue=array;