回到顶部bug

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 trigger
window.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);

    }
}