fd.js

var registerHandleFormSubmit = function() {
        $("#landingPage form").submit(function (e) {
            e.preventDefault();

            var $form = $(this);
            var $email = $form.find(".email");
            var $section = $form.closest("section");
            var $thankYou = $section.find(".thank-you");
            var $error = $section.find(".error");

            resetForm($email, $error);

            if (isValidateEmail($email)) {
                var token = $('input[name="__RequestVerificationToken"]', $form).val();

                $.ajax({
                    type: "POST",
                    url: "/umbraco/surface/subscribe/submit",
                    data: {
                        __RequestVerificationToken: token,
                        email: $email.val(),
                        listId: $form.data("list-id")
                    },
                    success: function (message) {

                        if (message.IsSuccess) {
                            handleSuccess($form, $thankYou, message);
                        } else {
                            handleFailure($form, $error, message);
                        }
                    },
                    error: function (e) {
                        console.log(e);
                    }
                });
            } else {
                $email.addClass("error");

                return false;
            }
        });

more.js

 var handleSuccess = function ($form, $thankYou, message) {
      $form.hide();
      $thankYou.show();
  }

  var handleFailure = function ($form, $error, message) {
      $error.text(message.ErrorMessage);
  }
  
  var resetForm = function ($email, $error) {
        $email.removeClass("error");
        $error.text("");
    }