Add Ajax Without partial

 Routes:   

get 'zzzz' => 'controllers#zzzz', :as => 'zzzz'

------

Controllers:

  include ActionView::Helpers::FormOptionsHelper

 skip_before_action :verify_authenticity_token, only: [:zzzz]

def zzzz

    bank_id = params[:bank_id]

    bank = Bank.find_by(id: bank_id)

    if bank.present?

      modes = options_for_auth_type(bank.mode)

    else

      modes = options_for_auth_type("E-mandate facility not available for this bank")

    end

    options = options_for_select(modes)

    render json: { options: modes }

  end

----------

html.erb file

<%=simple_form_for @customer, html: { class: 'form'} do |f|%>

<%= f.select :bank_id, options_for_select(select_bank, selected: f.object.bank_id), { include_blank: "Select Bank" }, { class: "chosen-select form-control mb-2 mr-sm-2", id: "bank_name", required: true } %>

<div class="col-sm-8">

                  <% if @customer.mode.present? %>

                    <%= f.select :auth_type, options_for_select(options_for_auth_type(@customer.mode), selected: f.object.auth_type), { include_blank: "Select Authorization" }, { class: "form-control mb-2 mr-sm-2"} %>

                  <% else %>

                    <%= f.select :auth_type, options_for_select([["Debit Card",'DebitCard'],["Net Banking",'NetBanking'],["Aadhaar", "Aadhaar"]], selected: f.object.auth_type), { include_blank: "Select Authorization" }, { class: "form-control mb-2 mr-sm-2"} %>

                  <% end %>

                </div>
<% end %>

<script type="text/javascript">

$(document).ready(function() {

  $('#bank_name').on('change', function() {

    var selectedBankId = $(this).val();  // Get selected bank ID

    $.ajax({

      url: '/zzzzz', // The URL where you send the request

      method: 'GET',

      data: { bank_id: selectedBankId },

      success: function(response) {

        var modes = response.options;

        var optionsHtml = '<option value="">Select Authorization</option>';

        $.each(modes, function(index, mode) {

          optionsHtml += '<option value="' + mode[1] + '">' + mode[0] + '</option>';

        });

        $('#customer_auth_type').html(optionsHtml);

      }

    });

  });

 });

</script>