js获取滚动条高度，文档DOM高度，浏览器可视化窗口的高度

//滚动条高度
getScrollTop: function () {
var scrollTop = 0, bodyScrollTop = 0, documentScrollTop = 0;
if (document.body) {
bodyScrollTop = document.body.scrollTop;
}
if (document.documentElement) {
documentScrollTop = document.documentElement.scrollTop;
}
scrollTop = (bodyScrollTop - documentScrollTop > 0) ? bodyScrollTop : documentScrollTop;
return scrollTop;
},
//文档高度
getScrollHeight: function () {
var scrollHeight = 0, bodyScrollHeight = 0, documentScrollHeight = 0;
if (document.body) {
bodyScrollHeight = document.body.scrollHeight;
}
if (document.documentElement) {
documentScrollHeight = document.documentElement.scrollHeight;
}
scrollHeight = (bodyScrollHeight - documentScrollHeight > 0) ? bodyScrollHeight : documentScrollHeight;
return scrollHeight;
},
//浏览器可是高度
getClientHeight: function () {
var windowHeight = 0;
if (document.compatMode == “CSS1Compat”) {
windowHeight = document.documentElement.clientHeight;
} else {
windowHeight = document.body.clientHeight;
}
return windowHeight;
},