效果如下，鼠标移上，先宽度变化，再高度变化，最后透明度变化，鼠标移出，再依次变回去。
要点一：
startrun(obj,attr,target,fn)
box.onmouseover = function(){
startrun(box,"width",200,function(){
startrun(box,"height",200,function(){
startrun(box,"opacity","100")
});
});
}
如上面，函数也可以做为参数使用，就可以达到先执行某个动作，再执行某个动作的效果了。
要点二：
if(cur == target){
clearInterval(obj.timer);
if(fn){
fn();
}
}
当运动到达目标点，关闭定时器，然后就可以执行新的函数了。
最后，上代码
<!DOCTYPE html>
<html>
<head>
<meta charset="gb2312" />
<title>无标题文档</title>
<style>
<!--
body{margin:0; padding:0; font:12px/1.5 arial;}
#box{width:100px; height:100px; position:absolute; background:#06c; left:0;filter:alpha(opacity=30); opacity:0.3;}
-->
</style>
<script>
<!--
function getstyle(obj,name){
if(obj.currentStyle){
return obj.currentStyle[name];
}else{
return getComputedStyle(obj,false)[name];
}
}
window.onload = function(){
var box = document.getElementById("box");
box.onmouseover = function(){
startrun(box,"width",200,function(){
startrun(box,"height",200,function(){
startrun(box,"opacity","100")
});
});
}
box.onmouseout = function(){
startrun(box,"height",100,function(){
startrun(box,"width",100,function(){
startrun(box,"opacity","30");
});
});
}
}
function startrun(obj,attr,target,fn){
clearInterval(obj.timer);
obj.timer = setInterval(function(){
var cur = 0;
if(attr == "opacity"){
cur = Math.round(parseFloat(getstyle(obj,attr))*100);
}else{
cur = parseInt(getstyle(obj,attr));
}
var speed = (target-cur)/8;
speed = speed>0?Math.ceil(speed):Math.floor(speed);
if(cur == target){
clearInterval(obj.timer);
if(fn){
fn();
}
}else{
if(attr == "opacity"){
obj.style.filter = "alpha(opacity="+(cur+speed)+")";
obj.style.opacity = (cur+speed)/100;
}else{
obj.style[attr] = cur + speed + "px";
}
}
},30)
}
//-->
</script>
</head>
<body>
<div id="box">
</div>
</body>
</html>