条件对象选择器

    $('.contact_tk .detail_up_next1').click(function(){

         var id = $(this).attr('data-id');

         var upid = $('.join_us li[data-id='+id+']').prev().attr('data-id');

         var downid = $('.join_us li[data-id='+id+']').next().attr('data-id');

    });

$(":radio[name='db_12'][value='2']").attr("checked","checked");