clear掉选择的再选中需要的
<select id="level" class="easyui-combobox" name="level" data-options=" multiple:true,
onSelect:onSelect" style="width:100px;">
<option value="'A+','A-','A'">A</option>
<option value="'A+','A-','A','B','C','D'" >All Level</option>
<option value="'B'">B</option>
<option value="'C'">C</option>
<option value="'D'">D</option>
</select>
<script>
function onSelect(r) {console.log(r)
if (r.text == 'All Level') {
$(this).combobox('clear').combobox('setValue', r.value)
}
else $(this).combobox('unselect', "'A+','A-','A','B','C','D'")
}
</script>
