$(window).height() 获取的是当前可视窗口的高度，也就是用户能看到的窗口的高度，是不变的（在窗口大小不变的前提下）
$(document).height() 获取的是窗口内文档的高度,这个高度随着文档内容的高度改变而改变
当窗口滚动条滚到最低端时，$(document).height() == $(window).height() + $(window).scrollTop()。
当窗口内文档高度不足浏览器窗口高度时，$(document).height()返回的是$(window).height()。
$("body").height() 如果body没有border、margin的话，$("body").height()==$(document).height(),但是还是不建议使用这种方式去获取文档内容高度
PS:如果你发现$(window).height()值有问题，返回的不是浏览器窗口的高度，那么看看是不是网页没有加上<!DOCTYPE>声明
滚动某个div中内容的情形如下
代码：
<html><head><script type="text/javascript" src="/jquery/jquery.js"></script><script type="text/javascript">$(document).ready(function(){ $(".btn1").click(function(){ $("div").scrollTop(100); }); $(".btn2").click(function(){ alert($("div").scrollTop()+" px"); });});</script></head><body><div >This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text. This is some text.</div><button class="btn1">把 scroll top offset 设置为 100px</button><br /><button class="btn2">获得 scroll top offset</button></body></html>当滚动条滚动到底部时，此时$("div").scrollTop() = 394px $("div").height()为div的高度200px不变