js实现sticky粘性定位

      var dom = document.querySelector('.count_money'), 
      domTop = dom.offsetTop;
      window.addEventListener('scroll',scrollFunc)
      function scrollFunc() {
      // 定位底部
          if(window.pageYOffset < domTop - window.innerHeight){
              dom.style.position = 'fixed';
              dom.style.bottom = 0;
          }else{
              dom.style.left = 'auto';
              dom.style.position = 'static'
          }
          // 定位顶部 
          if(window.pageYOffset > domTop){
              dom.style.position = 'fixed'
              dom.style.top = 0;
          }else{
              dom.style.position = 'static'
          }
      }
      scrollFunc()