解决Layui 表单提交数据为空的问题

<form class="layui-form" action="">
 <div class="layui-form-item">
  <label class="layui-form-label">输入框</label>
  <div class="layui-input-block">
   <input type="text" id=" " required lay-verify="required" placeholder="请输入标题" autocomplete="off" class="layui-input">
  </div>
 </div>
</form>

layui.use('form', function(){
 var form = layui.form;

 //监听提交
 form.on('submit(formDemo)', function(data){
   .msg(JSON.stringify(data.field));//此处显示输入内容
  return false;
 });
});