参考自一博客(https://www.cnblogs.com/abao0/p/6642288.html)内有慕课网教程(后发现有bug, 弃置不用了)

以下有问题, 当滚动条处于顶部时, 刷新页面, 回到顶部icon依然会出现.

//Page loading triggerwindow.onload = function () {    var oscrollBtn = document.getElementById('scrollBtn');    var timer = null;    var isTop = true;    //Gets the height of the visible window    var clientHeight = document.documentElement.clientHeight;//Triggered when the scroll bar rolls    window.onscroll = function () {        var osTop = document.documentElement.scrollTop || document.body.scrollTop;        if (osTop >= clientHeight) {            oscrollBtn.style.display = 'block';        } else {            oscrollBtn.style.display = 'none';        }        if (!isTop) {            clearInterval(timer);        }        isTop = false;    }    oscrollBtn.onclick = function () {        //Set timer        timer = setInterval(function () {            //Gets the height of the scroll bar            var osTop = document.documentElement.scrollTop || document.body.scrollTop;            //The scroll bar slows down            var ispeed = Math.ceil(osTop / 6);            document.documentElement.scrollTop = document.body.scrollTop = osTop - ispeed;            isTop = true;            if (osTop == 0) {                clearInterval(timer);            }        }, 30);    }}