bills_form.html.erb

<%= simple_form_for(@bill) do |f| %>
  <%= f.error_notification %>

  <div class="form-inputs">
    <div class="row">
      <div id="supplier_name">

      </div>
      <div class="col-md-11">
        <%= f.association :supplier, label_method: :fancy_name %>
      </div>

      <div class="col-md-1">
        <a href="#" data-toggle='modal' data-target='#modal_add_supplier' class="btn btn-default"><i class="fa fa-plus"></i></a>
      </div>
    </div>
  </div>

  <div class="form-actions">
    <%= f.button :submit, class: 'btn btn-default btn btn-primary btn-lg' %>
    <%= link_to t('view.action.back'), bills_path, class: 'btn btn-link btn-lg' %>
  </div>
<% end %>

<!-- MODAL SUPPLIER -->
<div id="modal_add_supplier" class="modal fade" role="dialog">
  <div class="modal-dialog" style="width: 800px; height: 400px;">
    <div class="modal-content">
      <div class="modal-header">
        <button type="button" class="close" data-dismiss="modal">&times;</button>
        <h4 class="modal-title">Selecione os Centros de Custo</h4>
      </div>
      <div class="modal-body">

        <%= render 'suppliers/form', modal: true %>

    </div>
    <div class="modal-footer">

    </div>
  </div>
</div>
</div>
<!-- MODAL SUPPLIER -->
<script>
$(document).ready(function(){
    $('[data-toggle="tooltip"]').tooltip();
    //$('#bill_amount').maskMoney();
    $("#bill_amount").maskMoney({ allowNegative: false, thousands:'.', decimal:',', affixesStay: false});
    // $('#currency2').maskMoney();
    //$("input[type=text].currency").setMask('decimal');

    $('#desconto').change(function(){
      $('.form-control.esconde').hide();
      $('.form-control.esconde').val('');
      $('#' + $(this).val()).show();
    });
});
</script>

supplier.js.erb

$('#supplier_name').append("<%= j render (@supplier) %>");
$('#modal_add_supplier').modal_success();

suppliers_controller.rb

def create
    @supplier = Supplier.new(supplier_params)

    respond_to do |format|
      if @supplier.save
        format.html { redirect_to @supplier, notice: 'Fornecedor Cadastrado com sucesso' }
        format.json { render action: 'show', status: :created, location: @supplier }
        # added:
        format.js   { render 'bills/supplier', status: :created, location: @supplier }
      else
        format.html { render action: 'new' }
        format.json { render json: @supplier.errors, status: :unprocessable_entity }
        # added:
        format.js   { render json: @supplier.errors, status: :unprocessable_entity }
      end
    end
  end

suppliers_form.html.erb

<% modal ||= false %>
<% remote = modal ? true : false %>
<%= simple_form_for(@supplier, remote: remote, html: {role: :form, 'data-model' => 'supplier'}) do |f| %>

  <%= f.error_notification %>

  <div class="form-inputs">

    <%= f.input :cnpj, autofocus: true %>
    <span class="help-block"></span>
    <%= f.input :fancy_name %>
    <span class="help-block"></span>
    <%= f.input :corporate_name %>
    <span class="help-block"></span>
    <%= f.input :state_registration %>
    <%= f.input :main_supplier %>
    <%= f.input :alternative_supplier %>

  </div>

  <div class="form-actions">
    <%= f.button :submit, class: 'btn btn-default btn btn-primary btn-lg' %>
    <%= link_to t('view.action.back'), suppliers_path, class: 'btn btn-link btn-lg' %>
  </div>
<% end %>