_ba_partial.html.erb

#--------ba_partial-------
<%= bootstrap_form_for ba, remote: true, data_id:  ba.id do |f| %>
		...
<div id="loader" class='load-ajax hide'></div>
<% end %>

ajax_code.js

$(document).ajaxStart(function() {
  $("#loader").show();
}).ajaxStop(function() {
  $("#loader").hide('slow');
});

index.html.erb

#-------index-------
<% @baz.order("id DESC").each do |ba| %>
	<%= render partial: 'ba_partial', locals: {ba: ba} %>
  <% end %>

index.js

$(document).on('submit', ".edit_ba", function( e ) {
        e.preventDefault();
    $.ajax( {
        url: $(this).attr('action'),
        type: 'POST',
        data: new FormData( this ),
        processData: false,
        contentType: false
     })
});