selectedField : stringDefault: 'selected'

    
 <select id="dropdown" width="200"></select>
 <script>
     $('#dropdown').dropdown({
         selectedField: 'newSelectedField',
         dataSource: [ { value: 1, text: 'One' }, { value: 2, text: 'Two', newSelectedField: true }, { value: 3, text: 'Three' } ]
     });
 </script>