<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>透明度</title>
<style type="text/css">
*{margin: 0;padding: 0;}
#box1{width: 200px;height: 200px;background: red;filter: alpha(opacity:30);opacity: 0.3;}
</style>
<script type="text/javascript">
window.onload=function(){
var v=document.getElementById('div1');
v.onmouseover=function(){
star(100);
}
v.onmouseout=function(){
star(30);
}
}
var timer=null;
var alpha=30;
function star(iTarget){
var v=document.getElementById('div1');
clearInterval(timer);
timer=setInterval(function(){
var speed=0;
if(alpha>iTarget){
speed=-10;
}else{
speed=10;
}
if(alpha==iTarget){
clearInterval(timer);
}else{
alpha=alpha+speed;
v.style.filter='alpha(opacity:'+alpha+')'
v.style.opacity=alpha/100;
}
},30)
}
</script>
</head>
<body>
<div id="box1"></div>
</body>
</html>你的id定义为box1,但是你上面在getElementById('div1')的时候都写成了div1