jquery ajax请求返回整个HTML内容

Question

所以我试图从我的服务器端php请求返回错误，但它返回整个页面的HTML内容。我有一个登录脚本，它做同样的事情并且工作，所以我开始变得非常沮丧。

我希望有人可以帮助我。

这是HTML：

<form id="register-form">
    <h2>Register</h2>
    <p><input type="text" class="form-control" id="username" name="username" placeholder="Username" autocomplete="off" /></p>
    <p><input type="text" class="form-control" id="email" name="email" placeholder="Email" autocomplete="off" /></p>
    <p><input type="password" class="form-control" id="password" name="password" placeholder="Password" autocomplete="off" /></p>
    <p><input type="password" class="form-control" id="passwordConfirm" name="passwordConfirm" placeholder="Confirm Password" autocomplete="off" /></p>
    <!-- DISPLAY ERRORS -->
    <p id="error" class="text-danger"></p>
    <input id="register-btn" type="submit" class="btn btn-lg btn-primary btn-block" name="registerBtn" value="Register Now" />
</form>

AJAX请求：

<script>
        $('#register-btn').click(function(evt) {
            evt.preventDefault();

            var username = $('#username').val();
            var email = $('#email').val();
            var password = $('#password').val();
            var passwordConfirm = $('#passwordConfirm').val();

            $.post("register.php", { username: username, email: email, password: password, passwordConfirm: passwordConfirm }, function(data) {
                    alert(data);
                //$('#error').html(data);
            });
        });
</script>

PHP：

if (isset($_POST['username']) && empty($_POST['email']) && empty($_POST['password']) && empty($_POST['passwordConfirm'])){

    $username           = trim($_POST['username']);
    $email              = trim($_POST['email']);
    $password           = trim($_POST['password']);
    $passwordConfirm    = trim($_POST['passwordConfirm']);

    if(empty($username) || empty($email) || empty($password) || empty($passwordConfirm)){ 
        echo 'All fields are required.';
        exit;
    }else if ($member->member_exists($username) === true) {
        echo 'That username is already taken.';
    }
    exit;
}