Question

How do I get this code to work correctly if I want (A.length == 0 && B.length == 1)?

    $(function() {
if (($('.thePrices').find('.addcartforlower').length == 0 ) && ($('.exclusive').length == 1 )) {
    $('.thePrices').find('a').after($('.wb_main').addClass('winbuyerset'));
$('.thePrices').find('.wb_main').before($('#compare'));   

      }
  });

Answer 1

extract

$('.thePrices').find('.addcartforlower').length

into a variable like so:

var addcartforlowerlength = $('.thePrices').find('.addcartforlower').length;

do something similar for the other side. Then your test will be simple:

if (addcartforlowerlength === 0 && exclusivelength === 1)

hope this helps