侧边栏广告和回到顶部

1. 侧边栏广告

    window.onload = window.onresize = window.onscroll = function() {
        var oDiv = document.getElementById("div1");

        //页面滚动的距离
        var scrollTop =
            document.documentElement.scrollTop || document.body.scrollTop;

        //DIV顶部距离可见窗口顶部的距离
        var t = (document.documentElement.clientHeight - oDiv.offsetHeight) / 2;

        //设置广告的位置
        oDiv.style.top = scrollTop + t + "px";
    }

2. 回到顶部

    window.onload = function() {
        var oBtn = document.getElementById("btn1");
        var timer = null;
        var isSys = false;

        //如果是用户拖动了滚动条，则停止滑动
        window.onscroll = function() {
            if (!isSys) {
                clearInterval(timer);
            }
            isSys = false;
        };

        oBtn.onclick = function() {
            timer = setInterval(function() {
                isSys = true;

                //页面滚动的距离
                var scrollTop =
                    document.documentElement.scrollTop || document.body.scrollTop;
                var iSpeed = Math.floor(-scrollTop / 8);

                //如果到达顶部，则清除定时器
                if (scrollTop === 0) {
                    clearInterval(timer);
                }

                document.documentElement.scrollTop =
                    document.body.scrollTop = scrollTop + iSpeed;
            }, 30);
        };
    };