jQ ajax select+option load + loading.gif

$j('#category_id').change(function() {
  		var category_id = $j('#category_id option:selected').val();
			$j("#subcategory_id").after('<div class="loading left"><img src="/templates/system/images/loading.gif" /></div>');
			if(category_id == '') {
				$j('#subcategory_id').attr('disabled', 'disabled');
			  	$j('.loading').remove();
			}
			else {
				jQuery.ajax({
				  url: 'index.php',
				  type: 'POST',
				  dataType: 'json',
				  data: {category_id: category_id},
				  success: function(data, textStatus, xhr) {
				  	$j('.loading').remove();
				  	$j('#subcategory_id').removeAttr('disabled');
				  	$j('#subcategory_id option').remove();
				  	var html = '<option selected="selected">Wszystkie</option>';
				    $j.each(data, function(val, name) {
	   		  			html = html+'<option value="'+val+'">'+name+'</option>'
				    });
				    $j('#subcategory_id').append(html);
 
				  },
				});	
			}
		});