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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
#img1 {
filter: alpha(opacity:20);
opacity: 0.2;
}
</style>
<script>
window.onload = function(){
var oImg = document.getElementById(‘img1‘);
oImg.onmouseover = function(){
startMove(100);
}
oImg.onmouseout = function(){
startMove(20);
}
}
var alpha = 20;
var timer = null;
function startMove(iTarget){
var oImg = document.getElementById(‘img1‘);
var iSpeed = 0;
clearInterval(timer);
timer = setInterval(function(){
if (alpha < iTarget) {
iSpeed = 2;
} else {
iSpeed = -2;
}
if (alpha == iTarget) {
clearInterval(timer);
} else {
alpha += iSpeed;
oImg.style.filter = ‘alpha(opacity:‘+ alpha +‘)‘;
oImg.style.opacity = alpha/100;
}
}, 30);
}
</script>
</head>
<body>
<img id="img1" src="images/bg_agency_banner.jpg" height="339" width="1360"/>
</body>
</html>
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原文地址：http://www.cnblogs.com/jimmzy/p/5034264.html
