javascript获取css中的样式值

 1     <body>
 2         <input type="button" id="btn" value="启动"/>
 3         <img src="timg.jpg" id="img" alt="" />
 4         <script type="text/javascript">
 5           
 6              window.onload = function()
 7              {
 8                  var time = null;
 9                  var img = document.getElementById("img");
10                  
11                 img.onmouseover = function()
12                 {
13                      startMove(img,100,10);
14 
15                    //alert(getComputedStyle(img,false).opacity)    
16                
17                 }
18                  img.onmouseout = function()
19                 {
20                     startMove(img,30,-10);
21                 }
22                 
23                  function startMove(obj,iTarget,ispeed)
24                {
25                     var icur =0;
26                       clearInterval(time);
27                       time = setInterval(function(){
28                             icur = Math.round((getComputedStyle(img,false).opacity)*100);  //为什么不能获取到呢
29                               if(icur == iTarget)
30                               {
31                                   clearInterval(time);
32                               }else{
33                                    obj.style.opacity = (icur + ispeed)/100 ; 
34                                    obj.style.filter = 'alpha(opacity = '+(icur + ispeed)+')';
35                               }
36                       },30)
37                }
38              }
39                
40         </script>
41     </body>

注意 ie下不支持

getComputedStyle