HTML部分：
<!DOCTYPE html>
<html>
<head>
<meta charset="gb2312"/>
<title>js动画-透明度变化</title>
<script src="http://libs.baidu.com/jquery/1.10.2/jquery.js"></script>
</head>
<body>
<div id="box">
<span>移动</span>
</div>
</body>
</html>
CSS部分：
* { margin: 0; padding: 0; font-family:"微软雅黑" } #box{ height:100px; width:100px; background-color:#0099CC; margin-top:200px; position:relative; /*透明度变化*/ left:0px; filter:alpha(opacity:30); opacity:0.3; } span{ display:block; color:blue; width:25px; height:100px; background-color:#FFFF99; position:absolute; left:100px; }
JS部分：
window.onload=function(){ var div1=document.getElementById("box"); div1.onmouseover=function(){ startMove(100); } div1.onmouseout=function(){ startMove(30); } } var timer=null; var alpha=30; function startMove(itarget){ clearInterval(timer); var div1=document.getElementById("box"); timer=setInterval(function(){ var speed=0; if(alpha>itarget){ speed=-10; }else{ speed=10; } if(alpha==itarget){ clearInterval(timer); }else{ alpha+=speed; div1.style.filter="alpha(opacity:"+alpha+")"; div1.style.opacity=alpha/100; } },100) }