侧边栏广告和回到顶部

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";
}

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);
};
};