<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title></title>
<style type="text/css">
#div1 {
width:200px;
height:200px;
background:red;
filter:alpha(opacity:30);
opacity:0.3;
}
</style>
<script type="text/javascript">
window.onload = function () {
var oDiv = document.getElementById("div1");
oDiv.onmousemove = function () {
startMove(100);
}
oDiv.onmouseout = function () {
startMove(30);
}
}
var timer = null;
var alpha = 30;
function startMove(iTarget) {
var oDiv = 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 += speed;
//IE
oDiv.style.filter = ‘alpha(opactiy :‘ + alpha + ‘)‘;
//google firefox
oDiv.style.opacity = alpha / 100;
}
}, 30);
}
</script>
</head>
<body>
<div id="div1">
</div>
</body>
</html>
原文：http://www.cnblogs.com/yzenet/p/4662667.html