javascript - jquery ajax html 警报中的 "\r\n\"

Question

我有一个如下所示的 ajax 请求

$(document).ready(function() {
    $(document).on('click', '#submit', function() {
        var UserName = $('#username').val();
        var PassWord = $('#password').val();
        console.log(UserName);
        $.ajax({
            type: 'POST',
            url: 'ajax/Login.php',
            dataType: "text",
            data: {
                username: UserName,
                password: PassWord
            },
            success: function(data) {
                alert(JSON.stringify(data));
                window.location='pages/mainpage.php';
            },
            error: function(data) {
                alert('Login Error');
                //window.location='../index.php';
            }
        });
    });
});

我的 php 是这样的

$username = mysql_real_escape_string($_POST['username']);
$password = mysql_real_escape_string($_POST['password']);

if (isset($username)) {
    $stmt = $dbh->prepare("SELECT * FROM userlist_tbl WHERE username = ? ");
    $stmt->bindValue(1, $username);
    $stmt->execute();
    $selected_row = $stmt->fetch(PDO::FETCH_ASSOC);
    if ($selected_row['username'] === $username) {
        if ($selected_row['password'] === $password) {
            $_SESSION['login_user'] = $username;
            echo "Welcome ".$username;
        }else{
    echo "Password incorrect";
}
    }
}else{
    echo "Username is empty";
}

当我没有在用户名中输入任何内容时，我希望警报将是用户名为空，与密码为空时相同，警报应该是密码不正确，但我得到了"\r\n\" 但如果在用户名中输入一些像 John 的内容，它会提醒 Welcome John"\r\n\" 为什么是发生这种情况？当用户名与密码相同时，如何让它提醒用户名为空？任何想法都被接受..

Answer 1

试试这个:在ajax部分，dataType: "text",更改为dataType: "json",并且服务器php代码是以下:可能有效

  //put this function top of this page
   ob_start(); 

    $username = mysql_real_escape_string($_POST['username']);
    $password = mysql_real_escape_string($_POST['password']);
       $json="";
            if (isset($username)) {


       $stmt = $dbh->prepare("SELECT * FROM userlist_tbl WHERE username = ? ");
            $stmt->bindValue(1, $username);
            $stmt->execute();
            $selected_row = $stmt->fetch(PDO::FETCH_ASSOC);
            if ($selected_row['username'] === $username) {
                if ($selected_row['password'] === $password) {
                    $_SESSION['login_user'] = $username;
                     $json.="Welcome ".$username;
                }else{
            $json.="Password incorrect";
        }
            }
        }else{
             $json.="Username is empty";
        }
   ob_end_clean(); 
   echo json_encode($json);

?>