layui 如何取得select下拉框选中的值

html:

 <form class="layui-form layui-form-pane" action="" lay-filter="example">
                <div class="layui-form-item">
                    <div class="layui-form-item">
                        <label class="layui-form-label"><i class="required-color">*</i>学校名称</label>
                        <div class="layui-input-inline">
                            <select name="s_id" lay-verify="required" lay-filter="school">
                                <option value=""></option>
                                {foreach $schoolData as $vo}
                                <option value="{$vo.id}">{$v