vue 监听滚动条

 created() {
    window.onscroll = () => {
      var scrollTop =
        document.documentElement.scrollTop || document.body.scrollTop;
      var windowHeight =
        document.documentElement.clientHeight || document.body.clientHeight;
      var scrollHeight =
        document.documentElement.scrollHeight || document.body.scrollHeight;
      if (scrollHeight ==( scrollTop - windowHeight )) {
        alert('已经滚动到底部了')
      }
    };
  },