原生态js回顶部

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width,initial-scale=1.0,minimum-scale=1.0,maximum-scale=1.0,user-scalable=no" />
    <title>Document</title>
    <style type="text/css">
    * {
        margin: 0;
        padding: 0;
    }

    .public_gotop {
        background-color: #858585;
        position: fixed;
        right: 2rem;
        bottom: 6rem;
        width: 3rem;
        height: 3rem;
        border-radius: 50%;
        background-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACAAAAAgCAYAAABzenr0AAABN0lEQVRYhe3Uuy4FURjFcZEjiMu76FwLiWuLhJJ4FU+gFwqNa1SuHQmtzhNoJRxB3H4Kc+LLGJdzDI1Z3cxe3/qvvfdk6uoKFSpUqEahFetYRtNfw9tx4k2HaPkreBuOvdcBmn8b3pyAKrrCTXjeQsNvwVtxFGAX6EAPyuH9bu7fRMbOL9EZ1ntTJbbRmBe8CfupY+/K8A2krmPzx9eRwPdS8O5P/IO4Df4NlGqFN2InhJXR+425oVSJtapLJPDtEHKNvirmR3AX5le+XQINydFVdIOBqnbwmjOaKrGE+q+GSl5/rxXdYqhaeMgbw33IW/ywRAJfTcGHa4WH3HE8hNyFzBKYD6YHTPwUHrKn8RTy57JM58niIybzgof8WTwnjLMsQz9OMZU3PDBmEkbn1+5ChQr9F70Ae6lHrD/JbEkAAAAASUVORK5CYII=);
        background-repeat: no-repeat;
        background-position: center;
        background-size: 60%;
        display: none;
    }
    </style>
</head>

<body>
    <div style="height: 500px; background: #E1A0F3"></div>
    <div style="height: 500px; background: #CE77B5"></div>
    <div class="public_gotop" id="gotop"></div>
    <script type="text/javascript">
    window.onload = function() {
        // 返回顶部
        var goTopEx = function() {
            var gtObj = document.getElementById("gotop");

            function getScrollTop() {
                return document.documentElement.scrollTop || document.body.scrollTop;
            }

            function setScrollTop(value) {
                document.documentElement.scrollTop = value;
                document.body.scrollTop = value;
            }
            window.onscroll = function() {
                getScrollTop() > 80 ? gtObj.style.display = "block" : gtObj.style.display = "none";
            }
            gtObj.onclick = function() {
                var goTop = setInterval(scrollMove, 10);

                function scrollMove() {
                    setScrollTop(getScrollTop() / 1.1);
                    if (getScrollTop() < 1) clearInterval(goTop);
                }
            }
        }()
    }
    </script>
</body>

</html>

效果如图：

备注解释：

function goTopEx() { //函数名goToEx
    var obj = document.getElementById("goTopBtn"); //获取id为goTopBtn的元素
    function getScrollTop() { //函数名为getScrollTop
        return document.documentElement.scrollTop; //返回document.documentElement(html)的滚动条的高度
    }

    function setScrollTop(value) { //函数名为setScrollTop,形参为value
        document.documentElement.scrollTop = value; //设置document.documentElement(html)的滚动条的高度为value
    }
    window.onscroll = function() { getScrollTop() > 0 ? obj.style.display = "" : obj.style.display = "none"; }; //当移动鼠标的时候,如果document.documentElement(html)的滚动条的高度>0,则obj显示,否则隐藏掉
    obj.onclick = function() { //点击obj
        var goTop = setInterval(scrollMove, 10); //每隔10毫秒发生scroolMove方法
        function scrollMove() { //函数名为scrollMove
            setScrollTop(getScrollTop() / 1.1); //设置document.documentElement(html)的滚动条的高度为getScrollTop()/1.1
            if (getScrollTop() < 1) clearInterval(goTop); //如果得到document.documentElement(html)的滚动条的高度<1,则清除掉scroolMove方法
        }
    };
}