[url=http://ejohn.org/blog/getboundingclientrect-is-awesome/]大神的结论[/url]：
Handling table border offsets.
Fixed positioned elements.
Scroll offsets within another element.
Borders of overflowed parent elements.
Miscalculation of absolutely positioned elements.
[img]https://developer.mozilla.org/@api/deki/files/788/=OffsetHeight.png[/img]
随着新锐浏览器都支持IE的getBoundingClientRect方法，我们得以用更简单更快捷更安全的方法来定位页面元素。getBoundingClientRect返回的是一个集合，分别为元素在浏览器可视区的四个角的坐标。
不过它在IE的标准模式存在一个奇怪的问题，html元素是有border的，默认是２px，并且是不可修改的；怪癖模式是没有的。详见[url=http://msdn.microsoft.com/en-us/library/ms536433(VS.85).aspx]http://msdn.microsoft.com/en-us/library/ms536433(VS.85).aspx[/url]
[quote]This method retrieves an object that exposes the left, top, right, and bottom coordinates of the union of rectangles relative to the client's upper-left corner. In Microsoft Internet Explorer 5, the window's upper-left is at 2,2 (pixels) with respect to the true client. [/quote]我们做一些测试（请分别在IE6与IE8中进行）：
1、标准模式，没有重设html的border
var getCoords = function(el){
var box = el.getBoundingClientRect(),
doc = el.ownerDocument,
body = doc.body,
html = doc.documentElement,
clientTop = html.clientTop || body.clientTop || 0,
clientLeft = html.clientLeft || body.clientLeft || 0,
top = box.top + (self.pageYOffset || html.scrollTop || body.scrollTop ) - clientTop,
left = box.left + (self.pageXOffset || html.scrollLeft || body.scrollLeft) - clientLeft
return { 'top': top, 'left': left };
};
其中self.pageYOffset相当于window.self.pageYOffset，是火狐的一个属性，相当于document.body.scrollTop。以下是它的定义：
Definition: The pageYOffset property is used to determine the Y coordinate of the scroll position in some browsers. This is not a reserved word so you can declare your own variable or function called pageYOffset but if you do then you will not be able to find or alter the scroll position of a window in some browsers
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