<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<style>
*{ margin:0; padding:0;}
#first{ width:200px;
height:200px;
background: #0F0;
filter:alpha(opacity:30);
opacity:0.3;}
</style>
<script>
window.onload=function(){
var block=document.getElementById('first');
block.onmouseover=function(){
change(100);
}
block.onmouseout=function(){
change(30);
}
}//onload
var timer=null;
var alpha=30;
function change(target){
clearInterval(timer);
var block=document.getElementById('first');
var speed=0;
setInterval(function(){
if(alpha>target){
speed = -1;
}else{
speed = 1;
}
if(alpha==target){
clearInterval(timer);
}else{
alpha+=speed
block.style.filter='alpha(opacity:'+alpha+')' ;
block.style.opacity=alpha/100; } },30);
}
</script>
</head>
<body>
<div id="first"></div>
</body>
</html>
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