text: class Abc {
      constructor() {
          this.xuanfu = $('.xuanfu');
      }
      init() {
          $(window).on('scroll', () => {
  
              let $top = $(window).scrollTop();
              if ($top >= 80) {
  
                  $('.xuanfu').stop(true).animate({
                      top: 0
                  });
  
              } else {
                  $('.xuanfu').stop(true).animate({
                      top: -50
                  });
              }
          });
      }
  }
  export {
      Abc
  }