如下效果，下面的5个元素，随便一个，鼠标移上去透明度渐渐增加，鼠标移出，透明度渐渐减小。
效果预览：
- 1
- 2
- 3
- 4
- 5
要点一：
var speed = 0;
if(target>obj.alpha){
speed = 5;
}else{
speed = -5;
}
根据目标值和当时值的对比，来决定是正向还是负向速度。
要点二：
for(i=0; i<runs_li.length; i++){
runs_li[i].timer = null;
runs_li[i].alpha = 30;
runs_li[i].onmouseover = function(){
startrun(this,100);
}
runs_li[i].onmouseout = function(){
startrun(this,30);
}
}
给每一个元素加上各自的透明度值，各自的透明度变化分开。
最后，上代码：
<!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>
body,ul,li{margin:0; padding:0;}
#runs{width:300px; margin:10px auto;}
#runs li{width:80px; height:80px; background:#06c; list-style:none; float:left; margin:10px; display:inline; filter:alpha(opacity=30); opacity:0.3;}
</style>
<script>
window.onload = function(){
var runs = document.getElementById("runs");
var runs_li = runs.getElementsByTagName("li");
var i=0;
for(i=0; i<runs_li.length; i++){
runs_li[i].timer = null;
runs_li[i].alpha = 30;
runs_li[i].onmouseover = function(){
startrun(this,100);
}
runs_li[i].onmouseout = function(){
startrun(this,30);
}
}
}
function startrun(obj,target){
clearInterval(obj.timer);
obj.timer = setInterval(function(){
var speed = 0;
if(target>obj.alpha){
speed = 5;
}else{
speed = -5;
}
if(obj.alpha == target){
clearInterval(obj.timer);
}else{
obj.alpha = obj.alpha + speed;
obj.style.filter = "alpha(opacity="+obj.alpha+")";
obj.style.opacity = obj.alpha/100;
}
},30)
}
</script>
</head>
<body>
<ul id="runs">
<li>1</li>
<li>2</li>
<li>3</li>
<li>4</li>
<li>5</li>
</ul>
</body>
</html>