Javascript 后端错误消息未发出警报。。！

我正在使用jquery来执行一个.php文件，但我的主要问题是，当从后端抛出错误时，我使用了一个警报来显示该错误。\u msg..但如果我故意提交错误…它只是移动到操作中指定的页面…没有弹出错误警报…请帮助我解决此问题。！！如果我错了，请原谅

这里是DB_Function.php

<?php
class DB_Functions {
    private $db;

    // constructor for database connection
    function __construct() {
        try {
            $hostname = "localhost";
            $dbname = "miisky";
            $dbuser = "root";
            $dbpass = "";
            $this->db = new PDO("mysql:host=$hostname;dbname=$dbname", $dbuser, $dbpass);
        }
        catch(PDOException $e)
        {
            die('Error in database requirments:'    . $e->getMessage());
        }
    }

    /**
      * Storing new user
      * returns user details of user
      */
  public function storeUser($fname, $lname, $email, $password, $mobile) {  
    try {
        $hash = md5($password);
        $sql = "INSERT INTO users(fname, lname, email, password, mobile, created_at) VALUES ('$fname', '$lname', '$email', '$hash', '$mobile', NOW())";
        $dbh = $this->db->prepare($sql);

        if($dbh->execute()){
            // get user details
            $sql = "SELECT * FROM users WHERE email = '$email' LIMIT 1";
            $dbh = $this->db->prepare($sql);
            $result = $dbh->execute();
            $rows = $dbh->fetch();
            $n = count($rows);
            if($n){
                return $rows;
            }
        }
    }
    catch (Exception $e) {
        die('Error accessing database: ' . $e->getMessage());
    }
    return false;
}

/*to check if user is
 already registered*/
  public function isUserExisted($email) {
    try{
        $sql = "SELECT email FROM users WHERE email = '$email' LIMIT 1";
        $dbh = $this->db->prepare($sql);
        $result = $dbh->execute();
        if($dbh->fetch()){
            return true;
        }else{
            return false;
        }
    }catch (Exception $e) {
        die('Error accessing database: ' . $e->getMessage());
    }
}
/*to check if user
exist's by mobile number*/
public function isMobileNumberExisted($mobile){
try{
    $sql = "SELECT mobile FROM users WHERE mobile = '$mobile' LIMIT 1";
    $dbh = $this->db->prepare($sql);
    $result = $dbh->execute();
    if($dbh->fetch()){
    return true;
    }else{
    return false;
    }
}catch(Exception $e){
    die('Error accessing database: ' . $e->getMessage());
}
}
//DB_Functions.php under construction 
//more functions to be added
}
?>

这里是相应的.html文件

<form method = "POST" name = "register" id = "register" class="m-t" role="form" action="login.html">

                    <div class="form-group">
                        <input type="text" name = "fname" id = "fname" class="form-control" placeholder="First Name" required="">
                    </div>
                    <div class="form-group">
                        <input type="text" name = "lname" id = "lname" class="form-control" placeholder="Last Name" required="">
                    </div>
                    <div class="form-group">
                        <input type="email" name = "email" id = "email" class="form-control" placeholder="Email" required="">
                    </div>
                    <div class="form-group">
                        <input type="password" name = "password" id = "password" class="form-control" placeholder="Password" required="">
                    </div>
                    <div class="form-group">
                        <input type="mobile" name = "mobile" id = "mobile" class="form-control" placeholder="Mobile No" required="">
                    </div>
                    <div  class="form-group" id="recaptcha_widget">
                                                        <div class="required">
                                                          <div class="g-recaptcha" data-sitekey="6Lc4vP4SAAAAABjh8AG"></div>
                                                       <!-- End Thumbnail-->
                                                      </div>
                                                      <?php include("js/captcha.php");?>
                    </div>
                    <div class="form-group">
                            <div cle the terms and policy </label></div>
                    </div>ass="checkbox i-checks"><label> <input type="checkbox"><i></i> Agre
                    <button type="submit" name = "submit" id = "submit" class="btn btn-primary block full-width m-b">Register</button>

                    <p class="text-muted text-center"><small>Already have an account?</small></p>
                    <a class="btn btn-sm btn-white btn-block" href="login.html">Login</a>
                <

/form>

阿格雷
登记
已经有帐户了吗
<
/表格>

表单提交在ajax操作之前执行操作，因此它会重新加载页面并使用表单提交而不是单击提交按钮

//execute's the function on click
    $("#register").on('submit',function(e){
       e.preventDefault(); // prevent page from reloading 

确定在尝试使用ajax时确保一切正常的步骤

第一：使用表单提交并使用

e.preventDefault（）以防止页面重新加载

//execute's the function on click
    $("#register").on('submit',function(e){
       e.preventDefault(); // prevent page from reloading
       alert('Form submited'); 
   });

如果警报弹出窗口和表单未重新加载页面，则下一步将使用ajax

  //execute's the function on click
    $("#register").on('submit',function(e){
       e.preventDefault(); // prevent page from reloading
       $.ajax({
          url: "register.php",
          type: "POST",
          dataType: "JSON",
          data: {success : 'success'},
          success : function(data){
              alert(data);
          }
       });
   });

和php（register.php）



此代码应使用“成功”警报框发出警报。。如果这一步很好，那么现在您的ajax和php文件已成功连接，然后传递变量并从注释中执行另一项操作
：

所以只有在显示注册成功后！我想提交表单并将其重定向到login.html

解决方案非常简单，包括在
.ajax（）
中添加
async
参数并将其设置为
false
。将
async
设置为
false
意味着在调用函数中的下一条语句之前，必须先完成正在调用的语句。如果设置了
async:true
，则该语句将开始执行，并将调用下一条语句，而不管该async语句是否已完成

您的jQuery应该是这样的：

$(document).ready(function(){
    //execute's the function on click
    $("#submit").click(function(e){

        /*jquery to call the url requested 
        and parse the data in json*/
        $.ajax({
            url: "register.php",
            type: "POST",
            data: {
                fname: $("#fname").val(),
                lname: $("#lname").val(),
                email: $("#email").val(),
                password: $("#password").val(),
                mobile: $("#mobile").val()
            },
            async: false,
            dataType: "JSON",
            /*Give out the alert box
            to display the results*/ 
            success: function (json){
                if(json.error){
                    alert(json.error_msg);
                    e.preventDefault();
                }else{
                    alert("Registeration successful!",json.user.email);
                    ('#register').submit();
                }
            },
            error: function(jqXHR, textStatus, errorThrown){
                alert(errorThrown);
            }
        });
    });
}); 

$(document).ready(function(){

    //execute's the function on click
    $("#submit").click(function(e){

        var status = $('form')[0].checkValidity();
        if(status){
            /*jquery to call the url requested 
            and parse the data in json*/
            $.ajax({
                url: "register.php",
                type: "POST",
                data: {
                    fname: $("#fname").val(),
                    lname: $("#lname").val(),
                    email: $("#email").val(),
                    password: $("#password").val(),
                    mobile: $("#mobile").val()
                },
                async: false,
                dataType: "JSON",
                /*Give out the alert box
                to display the results*/ 
                success: function (json){
                    if(json.error){
                        alert(json.error_msg);
                        e.preventDefault();
                    }else{
                        alert("Registeration successful!",json.user.email);
                        $('#register').submit();
                    }
                },
                error: function(jqXHR, textStatus, errorThrown){
                    alert(errorThrown);
                }
            });
        }

    });

}); 

因此，只有在注册成功的情况下，才能提交表格，否则不会

编辑：

首先，确保页面顶部有
，它代表html5，html5支持
必需的
属性

现在来谈谈前端验证。HTML5表单验证过程仅限于通过提交按钮提交表单的情况。明确地说，当通过
submit（）
方法提交表单时，不会执行验证。显然，这个想法是，如果您通过JavaScript提交表单，您应该进行验证

但是，您可以使用
checkValidity（）
方法根据HTML5属性定义的约束请求（静态）表单验证

为了简单起见，我删除了您的条款和条件复选框和Google ReCaptcha。您可以在以后的代码中合并这些内容

下面是您的HTML代码片段：

<form method = "POST" name = "register" id = "register" class="m-t" role="form" action="login.html">

    <div class="form-group">
        <input type="text" name = "fname" id = "fname" class="form-control" placeholder="First Name" required />
    </div>
    <div class="form-group">
        <input type="text" name = "lname" id = "lname" class="form-control" placeholder="Last Name" required />
    </div>
    <div class="form-group">
        <input type="email" name = "email" id = "email" class="form-control" placeholder="Email" required />
    </div>
    <div class="form-group">
        <input type="password" name = "password" id = "password" class="form-control" placeholder="Password" required />
    </div>
    <div class="form-group">
        <input type="mobile" name = "mobile" id = "mobile" class="form-control" placeholder="Mobile No" required />
    </div>

    <!--Your checkbox goes here-->
    <!--Your Google ReCaptcha-->

    <input type="submit" name = "submit" id = "submit" class="btn btn-primary block full-width m-b" value="Register" />

</form>

<p class="text-muted text-center"><small>Already have an account?</small></p>
<a class="btn btn-sm btn-white btn-block" href="login.html">Login</a>

在（'submit'，函数（e）{e.preventDefault（）；或$（“#submit”）。在（'submit'，函数（e）{e.preventDefault（）；@krishna$（“#register”）。在（'submit'，确定此代码以防止页面加载..并且您应该会收到警报，现在显示错误，但当我单击“确定”时在警报框中，它会自动在中执行操作tag@krishna在进入下一步之前，请检查每一步。首先检查ajax和php连接，确保它们已经连接。表单不会重新加载页面，然后编写php数据库code@krishna更新答案请参阅步骤，确保一切顺利离开长官…！！晚餐简单代码..和晚餐解释…！！！真的很好..长官..！！有人怀疑它限制前端验证..为什么如此长官..？@krishna你到底在哪里做前端验证？@krishna抱歉耽搁了。请清楚地解释你的问题。你有什么错误？什么不起作用？我看不到任何错误rd问题，除了这一行，
ass=“checkbox i-checks”>Agre
。你确定这是正确的吗？@krishna我已经更新了我的答案。请查看我答案的编辑部分。
$(document).ready(function(){
    //execute's the function on click
    $("#submit").click(function(e){

        /*jquery to call the url requested 
        and parse the data in json*/
        $.ajax({
            url: "register.php",
            type: "POST",
            data: {
                fname: $("#fname").val(),
                lname: $("#lname").val(),
                email: $("#email").val(),
                password: $("#password").val(),
                mobile: $("#mobile").val()
            },
            async: false,
            dataType: "JSON",
            /*Give out the alert box
            to display the results*/ 
            success: function (json){
                if(json.error){
                    alert(json.error_msg);
                    e.preventDefault();
                }else{
                    alert("Registeration successful!",json.user.email);
                    ('#register').submit();
                }
            },
            error: function(jqXHR, textStatus, errorThrown){
                alert(errorThrown);
            }
        });
    });
}); 

<form method = "POST" name = "register" id = "register" class="m-t" role="form" action="login.html">

    <div class="form-group">
        <input type="text" name = "fname" id = "fname" class="form-control" placeholder="First Name" required />
    </div>
    <div class="form-group">
        <input type="text" name = "lname" id = "lname" class="form-control" placeholder="Last Name" required />
    </div>
    <div class="form-group">
        <input type="email" name = "email" id = "email" class="form-control" placeholder="Email" required />
    </div>
    <div class="form-group">
        <input type="password" name = "password" id = "password" class="form-control" placeholder="Password" required />
    </div>
    <div class="form-group">
        <input type="mobile" name = "mobile" id = "mobile" class="form-control" placeholder="Mobile No" required />
    </div>

    <!--Your checkbox goes here-->
    <!--Your Google ReCaptcha-->

    <input type="submit" name = "submit" id = "submit" class="btn btn-primary block full-width m-b" value="Register" />

</form>

<p class="text-muted text-center"><small>Already have an account?</small></p>
<a class="btn btn-sm btn-white btn-block" href="login.html">Login</a>

$(document).ready(function(){

    //execute's the function on click
    $("#submit").click(function(e){

        var status = $('form')[0].checkValidity();
        if(status){
            /*jquery to call the url requested 
            and parse the data in json*/
            $.ajax({
                url: "register.php",
                type: "POST",
                data: {
                    fname: $("#fname").val(),
                    lname: $("#lname").val(),
                    email: $("#email").val(),
                    password: $("#password").val(),
                    mobile: $("#mobile").val()
                },
                async: false,
                dataType: "JSON",
                /*Give out the alert box
                to display the results*/ 
                success: function (json){
                    if(json.error){
                        alert(json.error_msg);
                        e.preventDefault();
                    }else{
                        alert("Registeration successful!",json.user.email);
                        $('#register').submit();
                    }
                },
                error: function(jqXHR, textStatus, errorThrown){
                    alert(errorThrown);
                }
            });
        }

    });

});