Display spinner with jQuery-ui autocomplete

Add below Class CSS in Your CSS style with loading.gif image

.ui-autocomplete-loading{
background:url('https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-2CAHF5Z8aPGaK1rsXDzE773kXI9aMrtoTK865ZzNo7VHuhrHJevNyh-dmcMVEDXdB_nMdMlkK1EokWTsbgQgmN7ToHUmWfN3B_JlxIlG5KPPxk5eADuQxyXbMrLSpgivPAzMwNu6l84/s320/loading.gif') no-repeat right center !important;
}

Gravity Form In Prevent duplicate form submit on back button

jQuery(function($){
       $(document).on('gform_post_render', function(e, form_id){
            $('#gform_ajax_frame_'+form_id).attr('src', 'about:blank');
       });
});