使用 ajaxForm Jquery 插件时返回 PHP 错误

我正在尝试制作一个使用 ajaxForm 和验证插件的登录脚本，但如果 PHP 提供错误，它就不知道了。这是我的Javascript

$(function login() {
$("#login").validate({ // initialize the plugin
    // any other options,
    onkeyup: false,
    rules: {
        email: {
            required: true,
            email: true
        },
        password: {
            required: true
        }
    }
});
$('form').ajaxForm({
    beforeSend: function() {
        return $("#login").valid();
    },
    success: function() {
        window.location="index.php";
    },
    error: function(e) {
        alert(e);
    }
});
});

请记住，我是JS的新手，可能有更好的方法可以做到这一点。我需要的是，如果在提交表单但用户名或密码错误时，我需要它不重定向，并发出错误警报，但这目前不起作用。我以前用谷歌搜索过这个，并在这里检查过，到目前为止什么也没找到。

编辑：使用以下代码，它仍然不起作用：

.JS

   $(function login() {
    $("#login").validate({ // initialize the plugin
        // any other options,
        onkeyup: false,
        rules: {
            email: {
                required: true,
                email: true
            },
            password: {
                required: true
            }
        }
    });
    $("#login").submit(function(e) {
        e.preventDefault();
            $.ajax({
                type : "POST",
                dataType : "json",
                cache : false,
                url : "/doLogin",
                data : $(this).serializeArray(),
                success : function(result) {
                    if(result.result == "success"){
                        window.location = "/index.php";
                    }else if(result.result == "failure"){
                        $("#alert").html("Test");
                    }
               },
                error : function() {
                    $("#failure").show();
                    $(".btn-load").button('reset');
                    $("#email").focus();
                }
            });
    });
    }); 

.HTML

<div class="shadowbar">
<div id="alert"></div>
<form id="login" method="post" action="/doLogin">
<fieldset>
 <legend>Log In</legend>
<div class="input-group">
  <span class="input-group-addon">E-Mail</span>
  <input type="email" class="form-control" name="email" value="" /><br />
</div>
<div class="input-group">
  <span class="input-group-addon">Password</span>
  <input type="password" class="form-control" name="password" />
  </div>
</fieldset>
<input type="submit"  class="btn btn-primary" value="Log In" name="submit" />
</form></div>

.PHP

public function login() {
    global $dbc, $layout;
    if(!isset($_SESSION['uid'])){
        if(isset($_POST['submit'])){
            $username = mysqli_real_escape_string($dbc, trim($_POST['email']));
            $password = mysqli_real_escape_string($dbc, trim($_POST['password']));
            if(!empty($username) && !empty($password)){
                $query = "SELECT uid, email, username, password, hash FROM users WHERE email = '$username' AND password = SHA('$password') AND activated = '1'";
                $data = mysqli_query($dbc, $query);
                if((mysqli_num_rows($data) === 1)){
                    $row = mysqli_fetch_array($data);
                    $_SESSION['uid'] = $row['uid'];
                    $_SESSION['username'] = $row['username'];
                    $_SERVER['REMOTE_ADDR'] = isset($_SERVER["HTTP_CF_CONNECTING_IP"]) ? $_SERVER["HTTP_CF_CONNECTING_IP"] : $_SERVER["REMOTE_ADDR"];
                    $ip = $_SERVER['REMOTE_ADDR'];
                    $user = $row['uid'];
                    $query = "UPDATE users SET ip = '$ip' WHERE uid = '$user' ";
                    mysqli_query($dbc, $query);
                    setcookie("ID", $row['uid'], time()+3600*24);
                    setcookie("IP", $ip, time()+3600*24);
                    setcookie("HASH", $row['hash'], time()+3600*24);
                    header('Location: /index.php');
                    exit();
                } else {
                    $error = '<div class="shadowbar">It seems we have run into a problem... Either your username or password are incorrect or you haven''t activated your account yet.</div>' ;
                    return $error;
                    echo "{'"result'":'"failure'"}";
                }
            } else {
                $error = '<div class="shadowbar">You must enter both your username AND password.</div>';
                return $error;
                $err = "{'"result'":'"failure'"}";
                echo json_encode($err);
            }
            echo "{'"result'":'"success'"}";
        }
    } else {
        echo '{"result":"success"}';
        exit();
    }
    return $error;
}