JS 监听滚动条事件

/**
* 获取滚动条位置
*/
function getScrollTop() {
   var scrollPos;
   if (window.pageYOffset)
   {
       scrollPos = window.pageYOffset;
   }
   else if (document.compatMode && document.compatMode != 'BackCompat')
   {
       scrollPos = document.documentElement.scrollTop;
   }
   else if (document.body)
   {
       scrollPos = document.body.scrollTop;
   }
   return scrollPos;
}

/**
 * 监听滚动条 逻辑根据自己需求来哦
 */
window.onscroll = function () {
    let scrollPos = getScrollTop();
    console.log("scrollPos：",scrollPos);
    if (scrollPos == 0) {
        alert("页面已到顶部")
    }
}