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用document.documentElement取代document.body的原因分析

IE6在页面内容超出窗口大小时将宽度属性scrollWidth、clientWidth、offsetWidth都解释为内容实际宽度 。
上次的测试说明了document.body属性并不会给我们返回预期的结果，比如我们用document.body.clientHeight原本想取得“页面可见区域高度”，可实际上返回的是“页面实际内容高度” 。
那我们怎么办呢？难道加上了文档DTD类型之后就再也不能取到“可见区域高度”和“内容实际宽度”等等属性了吗？
复制代码 代码如下:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>documentElement</title>
<style type="text/css">
body{margin:0;padding:0;font:12px/150% arial;}
</style>
<script type="text/javascript">
function a() {
var scrollTop;
var scrollLeft;
if (typeof window.pageYOffset != undefined) {
scrollTop = window.pageYOffset;
scrollLeft = window.pageXOffset;
}
else if (typeof document.compatMode != undefined && document.compatMode != BackCompat) {
scrollTop = document.documentElement.scrollTop;
scrollLeft = document.documentElement.scrollLeft;
}
else if (typeof document.body != undefined) {
scrollTop = document.body.scrollTop;
scrollLeft = document.body.scrollLeft;
}
var scrollHeight = document.documentElement.scrollHeight;
var scrollWidth = document.documentElement.scrollWidth;
var clientWidth = document.documentElement.clientWidth;
var clientHeight = document.documentElement.clientHeight;
var offsetWidth = document.documentElement.offsetWidth;
var offsetHeight = document.documentElement.offsetHeight;
var screenTop = window.screenTop;
var screenBottom = window.screenBottom;
var screenLeft = window.screenLeft;
var sheight = window.screen.height;
var swidth = window.screen.width;
var availHeight = window.screen.availHeight;
var availWidth = window.screen.availWidth;
document.getElementById(scrollTop).value = scrollTop;
document.getElementById(scrollLeft).value = scrollLeft;
document.getElementById(scrollHeight).value = scrollHeight;
document.getElementById(scrollWidth).value = scrollWidth;
document.getElementById(clientWidth).value = clientWidth;
document.getElementById(clientHeight).value = clientHeight;
document.getElementById(offsetWidth).value = offsetWidth;
document.getElementById(offsetHeight).value = offsetHeight;
document.getElementById(screenTop).value = screenTop;
document.getElementById(screenBottom).value = screenBottom;
document.getElementById(screenLeft).value = screenLeft;
document.getElementById(sheight).value = sheight;
document.getElementById(swidth).value = swidth;
document.getElementById(availHeight).value = availHeight;
document.getElementById(availWidth).value = availWidth;
}
</script>
</head>
<body>
<div style="width:420px;height:470px;margin:0 auto;font-size:12px; border:solid 5px #ccc;">
<center>
<table width="400" border="0" cellspacing="0" cellpadding="0" style="font-size:12px;margin-top:20px;">
<tr>
<td width="187" align="right">scrollTop（滚动条卷过的高）：</td>
<td width="10"> </td>
<td width="209"><input type="text" name="scrollTop" id="scrollTop" /></td>
</tr>
<tr>
<td align="right">scrollLeft（滚动条卷过的宽）：</td>
<td> </td>
<td><input type="text" name="scrollLeft" id="scrollLeft" /></td>
</tr>
<tr>
<td align="right">scrollHeight（内容实际高度）：</td>
<td> </td>
<td><input type="text" name="scrollHeight" id="scrollHeight" /></td>
</tr>
<tr>
<td align="right">scrollWidth（内容实际宽度）：</td>
<td> </td>
<td><input type="text" name="scrollWidth" id="scrollWidth" /></td>
</tr>
<tr>
<td align="right">clientWidth（可见区域宽）：</td>
<td> </td>
<td><input type="text" name="clientWidth" id="clientWidth" /></td>
</tr>
<tr>
<td align="right">clientHeight（可见区域高）：</td>
<td> </td>
<td><input type="text" name="clientHeight" id="clientHeight" /></td>
</tr>
<tr>
<td align="right">offsetWidth（加滚动条宽？）：</td>
<td> </td>
<td><input type="text" name="offsetWidth" id="offsetWidth" /></td>
</tr>
<tr>
<td align="right">offsetHeight（加滚动条高？）：</td>
<td> </td>
<td><input type="text" name="offsetHeight" id="offsetHeight" /></td>
</tr>
<tr>
<td align="right">screenTop：</td>
<td> </td>
<td><input type="text" name="screenTop" id="screenTop" /></td>
</tr>
<tr>
<td align="right">screenBottom：</td>
<td> </td>
<td><input type="text" name="screenBottom" id="screenBottom" /></td>
</tr>
<tr>
<td align="right">screenLeft：</td>
<td> </td>
<td><input type="text" name="screenLeft" id="screenLeft" /></td>
</tr>
<tr>
<td align="right">sheight（分辨率高）：</td>
<td> </td>
<td><input type="text" name="sheight" id="sheight" /></td>
</tr>
<tr>
<td align="right">swidth（分分辨率宽）：</td>
<td> </td>
<td><input type="text" name="swidth" id="swidth" /></td>
</tr>
<tr>
<td align="right">availHeight：</td>
<td> </td>
<td><input type="text" name="availHeight" id="availHeight" /></td>
</tr>
<tr>
<td align="right">availWidth：</td>
<td> </td>
<td><input type="text" name="availWidth" id="availWidth" /></td>
</tr>
</table>
<a href="javascript:a()" style="height:20px;display:block;">内容高度是400PX，点击查看所有属性值</a>
</center>
</div>
</body>
</html>

其实，我们可以用document.documentElement代替document.body来获取我们想要的结果 将代码中的document.body替换为document.documentElement，再来看看各浏览器下的实际结果：
ii测试结果表明，IE系列浏览器对document.documentElement属性的解释是正确的，其它标准浏览器将offsetHeight解释成 了scrollHeight 。火狐和netscape更是把这两个属性调换了过来 。不过总的来说各属性都可以有个相应的解释，不会像 document.body一样只有可怜的两种解释 。

终于可以放心地使用JS方法获取各种页面高宽属性了吧^_^!