“\r\n\” in alert for jquery ajax html

Question

I have an ajax request that looks like this

$(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';
            }
        });
    });
});

and my php is like this

$username = mysql_real_escape_string($_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";
}

When i dont put anything in username i am expecting that the alert will be Username is empty same as when password is empty alert should be Password incorrect but i am getting "\\r\\n\\" but if put some in username like John it will alert Welcome John"\\r\\n\\" why is this happening?how to make it alert Username is empty when username is empty same with password?any idea is accepted..

Answer 1

我将isset更改为!empty解决了问题

Answer 2

Try this: in ajax section, dataType: "text", change to dataType: "json", and server php code is following: it may work

  //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);

?>