app/views/assets/_search.html.erb
<% form_tag 'search', { onSubmit: "Element.show('spinner');" } do -%>
<%= text_field_tag :asset_search %>
<%= image_tag 'small-spinner.gif', id: 'spinner', style: 'display:none;' %>
<% end %>
<%= observe_field(:asset_search,
frequency: 0.5,
update: :results,
loading: "Element.show('spinner')",
complete: "Element.hide('spinner');",
url: { controller: 'assets', action: 'search' },
with: 'search' )%>