PHP + Ajax Login

 $user = new User(array("username" => $_POST['username'], "password" => $_POST['password']));
 $user->Login();

Put the code above into an login.php controller file (including your users class). Or write a general controller that handles the requests.

whole issue is in jquery use this instead

$(document).ready(function() {
  $('#loginform').submit(function(e) {
    e.preventDefault();
    $.ajax({
       type: "POST",
       url: '/class/login.php',
       data: $(this).serialize(),
       success: function(data)
       {
          if (data === 'Login') {
            window.location = '/user-page.php';
          }
          else {
            alert('Invalid Credentials');
          }
       }
   });
 });
});