只想在滚动每个部分时添加类

Question

我正在尝试为每个部分添加一个类并删除一个类，以便当用户向下滚动时标题徽标会更改。

http://bitmontrade.com/sample/papa/

我现在在jQuery下面所做的操作删除了现有的div主题固定标头类，但是我无法获得addClass()的内容

(function() {
  // Override the addClass to prevent fixed header class from being added
  var addclass = jQuery.fn.addClass;
  jQuery.fn.addClass = function() {
    var result = addclass.apply(this, arguments);
    var section1 =
      jQuery('#main-header').removeClass('et-fixed-header');
    return result;
  }
})();

jQuery(function($) {
  $(document).ready(function() {
    var s = $('#marketwith');
    var pos = s.position();
    $(window).scroll(function() {
      var windowpos = $(window).scrollTop();
      var section1 = $("#markettitle").offset().top
      if (windowpos >= pos.top & windowpos <= section1) {
        $('#main-header').removeClass('et-fixed-header');
        $('#main-header').addClass('fixed-logo-change');
      } else {
        $('#main-header').removeClass('et-fixed-header');
        $('#main-header').addClass('fixed-logo-change1');
      }
    });
  });
});

.fixed-logo-change #logo {
  content: url(http://bitmontrade.com/sample/papa/wp-content/uploads/2019/03/logofixed.png);
}

.fixed-logo-change1 #logo {
  content: url(http://bitmontrade.com/sample/papa/wp-content/uploads/2019/03/logomain.png);
}

预先感谢