获取元素在浏览器中的绝对位置（从jquery1.8中抠出来）

<style>
html,body{margin:0;padding:0;}
.d1{margin-left:40px;background:red;width:2000px;height:100px;position:relative;}
.d2{margin-left:40px;background:blue;width:1000px;height:80px;}
</style>

<div id="d1" class="d1">
    <div id="d2" class="d2"></div>
</div>

 1 function getWindow( elem ) {
 2     return mylibs.isWindow( elem ) ?
 3         elem :
 4         elem.nodeType === 9 ?
 5             elem.defaultView || elem.parentWindow :
 6             false;
 7 };
 8
 9 var mylibs = {
10     isWindow: function( obj ) {
11         return obj != null && obj == obj.window;
12     },
13     //获取元素在浏览器中的绝对位置
14     offset:function(elem){
15         var docElem, win, clientTop, clientLeft, scrollTop, scrollLeft,
16             box = { top: 0, left: 0 },
17             doc = elem && elem.ownerDocument;
18
19         docElem = doc.documentElement;
20         //黑莓5 ios3(iphoe) 没有getBoundingClientRect
21         if ( typeof elem.getBoundingClientRect !== "undefined" ) {
22             box = elem.getBoundingClientRect();
23         }
24         win = getWindow( doc );
25
26         clientTop  = docElem.clientTop  || document.body.clientTop  || 0;
27         clientLeft = docElem.clientLeft || document.body.clientLeft || 0;
28         scrollTop  = win.pageYOffset || docElem.scrollTop;
29         scrollLeft = win.pageXOffset || docElem.scrollLeft;
30         return {
31             top: box.top  + scrollTop  - clientTop,
32             left: box.left + scrollLeft - clientLeft
33         };
34     }
35 };
36
37 document.getElementById(‘d2‘).onclick = function(){
38     alert(mylibs.offset(this).left);
39 };