此表单验证插件会对表单字段进行验证，实时提示用户输入信息，用户体验非常好，验证提示紧随input框！

以下为表单验证案例代码：

<script type="text/javascript" src="jquery-3.2.1.js"></script>
<script type="text/javascript" src="jquery.validate.min.js"></script>    //引入的插件
<script type="text/javascript">
    $(document).ready(function(){
        formValidate();                               //表单验证函数
    });
    function formValidate(){
        $("#sendmail").validate({                      //#sendmail表单id
            errorElement : "span",                     //错误信息将放入此标签内
            errorClass: "error_input" ,                //验证出错时使用的css class
            success: "valid" ,                         //自定义验证成功时的动作
            errorPlacement: function(error, element) { //自定义错误消息的显示位置

                element.next().html(error);     //error错误信息，element错误产生的input
            },
                rules: {
                    "from":{
                        required: true
                    },
                    "fromName":{
                        required: true
                    },
                    "to":{
                        required: true
                    },
                    "url":{
                        required: true
                    },
                    "subject":{
                        required: true
                    },
                    "html":{
                        required:true
                    },
                    "contry":{
                        required:true
                    }
                },
            messages: {
                "from":{
                    required: '请输入公司名称'
                },
                "fromName":{
                    required: '请选择省份'
                },
                "to":{
                    required: '请选择城市'
                },
                "url":{
                    required: '请选择县/区'
                },
                "subject":{
                    required: '请输入地址'
                },
                "html":{
                    required:'请选择国家区号'
                },
                "contry":{
                    required:'请选择国家区号'
                }
            },
            submitHandler: function(form){ //表单提交句柄,为一回调函数，带一个参数：form

                form.submit();    //提交表单
            }
        });

    };

</script>
<style type="text/css">
    .error_input{color:red;}                         //错误提示的样式
</style>
<form action="#" method="post" id="sendmail" name="sendmail">
    <p>发件邮箱：<input id="from" placeholder="银行账号"  name="from" type="email" required/><span></span></p>
    <p>发件姓名：<input id="fromName" placeholder="银行账号" name="fromName" type="text" required/><span></span></p>
    <p>收件邮箱：<input id="to" placeholder="银行账号" name="to" type="email" required/><span></span></p>
    <p>url：<input id="url" name="url" placeholder="银行账号" type="email" required/><span></span></p>
    <p>发件主题：<input id="subject" placeholder="银行账号" name="subject" type="text" required/><span></span></p>
    <p>选择类别：<select id="contry" name="contry">
            <option value ="中国">中国</option>
            <option value ="美国">美国</option>
            <option value="日本">日本</option>
            <option value="俄罗斯">俄罗斯</option>
            <option value="法国">法国</option>
            <option value="德国">德国</option>
        </select>
        <span></span></p>
    <p>邮件内容：<textarea id="html" placeholder="银行账号" name="html" cols="120" rows="6" required></textarea><span></span></p>
    <p>附　　件：<input name="submit" type="submit" value="提交"/></p>
</form>