该实例可实现鼠标移上，先宽度变化，再高度变化，最后透明度变化，鼠标移出，再依次变回去的效果。
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> </div> </body> </html>