JS实现div居中

 1     <!DOCTYPE html> 
 2     <html> 
 3     <head> 
 4     <meta charset="utf-8" /> 
 5     <title>JS实现div居中</title> 
 6     <style> 
 7     /*外层div居中*/
 8     #main {
 9         position: absolute;        /*极为重要*/
10         background-color: blue;
11         width:400px;
12         height:200px;
13         /*left:50%;
14         top:50%; 
15         margin-left:-200px;
16         margin-top:-100px;*/
17         border:1px solid #00F;
18     } 
19  
20     #content {
21         position: absolute;        /*极为重要*/
22         background-color: yellow;
23         width: 200px;
24         height: 100px;
25         /*left:50%;
26         top:50%; 
27         margin-left:-100px;
28         margin-top:-50px;*/
29         
30         /*div内部文字居中*/
31         text-align: center;
32         line-height:100px;        /*行间距和div宽度相同*/
33     }
34     </style> 
35     <body> 
36         <div id="main">
37             <div id="content">
38                 Sun
39             </div>
40         </div>
41     <script type="text/javascript">
42     window.onload = function() {
43         // 获取浏览器窗口
44         var windowScreen = document.documentElement;
45         // 获取main的div元素
46         var main_div = document.getElementById("main");
47         // 通过窗口宽高和div宽高计算位置
48         var main_left = (windowScreen.clientWidth - main_div.clientWidth)/2 + "px";
49         var main_top = (windowScreen.clientHeight - main_div.clientHeight)/2 + "px";
50         // 位置赋值
51         main_div.style.left = main_left;
52         main_div.style.top = main_top;
53 
54         // 获取mcontent的div元素
55         var content_div = document.getElementById("content");
56         var content_left = (main_div.clientWidth - content_div.clientWidth)/2 + "px";
57         var content_top = (main_div.clientHeight - content_div.clientHeight)/2 + "px";
58         content_div.style.left = content_left;
59         content_div.style.top = content_top;
60 
61     }
62     </script> 
63     </body> 
64     </html>