MooTools下的返回顶部功能的实现实例页面

.backToTop {
display: none;
width: 18px;
line-height: 1.2;
padding: 5px 0;
background-color: #000;
color: #fff;
font-size: 12px;
text-align: center;
position: fixed;
_position: absolute;
right: 10px;
bottom: 100px;
_bottom: "auto";
cursor: pointer;
opacity: .6;
filter: Alpha(opacity=60);
}

(function() {
var $backToTopTxt = "返回顶部", $backToTopEle = new Element("div", {
"class": "backToTop",
title: $backToTopTxt
}).set("text", $backToTopTxt).addEvent("click", function() {
var st = document.getScroll().y, speed = st / 6;
var funScroll = function() {
st -= speed;
if (st <= 0) { st = 0; }
window.scrollTo(0, st);
if (st > 0) { setTimeout(funScroll, 20); }
};
funScroll();
}).inject(document.body), $backToTopFun = function() {
var st = document.getScroll().y, winh = window.getSize().y;
(st > 0)? $backToTopEle.setStyle("display", "block"): $backToTopEle.setStyle("display", "none");
//IE6下的定位
if (!window.XMLHttpRequest) {
$backToTopEle.setStyle("top", st + winh - 166);
}
};
window.addEvents({
scroll: $backToTopFun,
domready: $backToTopFun
});
})();