Jquery获取select 控件的change事件时选中的值

<div class="col-sm-9 col-xs-12">
                    <select id="groupid" class="form-control" style="float: left" name="groupid">
                        <option value="0">请选择</option>
                        <option value="2">2</option>
                        <option value="4">4</option>
                        <option value="6">6</option>
                        <option value="8">8</option>
                    </select>
                    <div class="help-block"></div>
                </div>

<script type="text/javascript">
    $(function() {
        $("#groupid").change(function(){
            alert($(this).val());
        });
    });
</script>