表單驗證提示插件validate

此表單驗證插件會對表單字段進行驗證，實時提示用戶輸入信息，用戶體驗非常好，驗證提示緊隨input框！

以下為表單驗證案例代碼：

<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();                               //表單驗證函數
    });
    function formValidate(){
        $("#sendmail").validate({                      //#sendmail表單id
            errorElement : "span",                     //錯誤信息將放入此標簽內
            errorClass: "error_input" ,                //驗證出錯時使用的css class
            success: "valid" ,                         //自定義驗證成功時的動作
            errorPlacement: function(error, element) { //自定義錯誤消息的顯示位置

                element.next().html(error);     //error錯誤信息，element錯誤產生的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: '請輸入公司名稱'
                },
                "fromName":{
                    required: '請選擇省份'
                },
                "to":{
                    required: '請選擇城市'
                },
                "url":{
                    required: '請選擇縣/區'
                },
                "subject":{
                    required: '請輸入地址'
                },
                "html":{
                    required:'請選擇國家區號'
                },
                "contry":{
                    required:'請選擇國家區號'
                }
            },
            submitHandler: function(form){ //表單提交句柄,為一回調函數，帶一個參數：form

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

    };

</script>
<style type="text/css">
    .error_input{color:red;}                         //錯誤提示的樣式
</style>
<form action="#" method="post" id="sendmail" name="sendmail">
    <p>發件郵箱：<input id="from" placeholder="銀行賬號"  name="from" type="email" required/><span></span></p>
    <p>發件姓名：<input id="fromName" placeholder="銀行賬號" name="fromName" type="text" required/><span></span></p>
    <p>收件郵箱：<input id="to" placeholder="銀行賬號" name="to" type="email" required/><span></span></p>
    <p>url：<input id="url" name="url" placeholder="銀行賬號" type="email" required/><span></span></p>
    <p>發件主題：<input id="subject" placeholder="銀行賬號" name="subject" type="text" required/><span></span></p>
    <p>選擇類別：<select id="contry" name="contry">
            <option value ="中國">中國</option>
            <option value ="美國">美國</option>
            <option value="日本">日本</option>
            <option value="俄羅斯">俄羅斯</option>
            <option value="法國">法國</option>
            <option value="德國">德國</option>
        </select>
        <span></span></p>
    <p>郵件內容：<textarea id="html" placeholder="銀行賬號" name="html" cols="120" rows="6" required></textarea><span></span></p>
    <p>附　　件：<input name="submit" type="submit" value="提交"/></p>
</form>