How can I invoke an AJAX response?

Question

I have a Drupal 8 form I want to show via JavaScript code to make it appear as a popup across multiple pages. The form is rendered through an AJAX response in a controller. I can see the response using $.ajax(). How can I invoke the AJAX response to display on the page?

The JavaScript code is the following one.

$(document).ready(function() {
  $.ajax({
    url: '/aao_additions/modal_form',
    // Data parameter is the ajax response data for the intersitial popup.
    success: function(data, status, jqxhr) {
      console.log(data);
      console.log(status);
      var popup = Drupal.ajax({
        url: "",
        base: false,
        element: false,
        progress: false,
      });
      // Simulate an AJAX response having arrived, and let the Ajax system handle it.
      popup.success(data, "success");
    },
    // Error function for if the modal form cannot be loaded.
    error: function(xhr, desc, err) {
      console.log(xhr);
      console.log("Desc: " + desc + "\nErr:" + err);
    },
  });
});

I receive an error on Drupal.ajax. I think it is preventing the response rendering.