代码如下，但IE没有动画效果，有大神可以解释下吗？

源自：2-2 JS透明度动画

window.onload=drag;

function drag(){

var div1=document.getElementById('div1');

div1.onmouseover=function(){changeOpacity(100);}

div1.onmouseout=function(){changeOpacity(20);}

}

var timer=null;

var alpha=20;

function changeOpacity(num){

var div1=document.getElementById('div1');

clearInterval(timer);

timer=setInterval(function(){

var speed=0;

if(num>alpha){speed=10;} else{speed=-10;}

if(alpha==num){clearInterval(timer);}else{

alpha+=speed;

div1.style.filter='alpha(opacity:'+alpha+')';

div1.style.opacity=alpha/100;}

},50);

}

提问者：yiyi30 2016-01-07 16:48