JavaScript多物体运动框架实现放大缩小效果

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>运动框架</title>
<style>
#div1{ width:100px; height:100px; background:red; position:absolute; left:0; top:50px; opacity:0.3; filter:alpha(opacity=30);}
</style>
<script>
window.onload = function()
{
 var oBtn = document.getElementById('btn1');
 var oDiv = document.getElementById('div1');
 oBtn.onclick = function()
 {
 startMove(oDiv, {width:200, height:200, opacity:100}, function(){
  startMove(oDiv, {width:100, height:100, opacity:30});
 });
 };
};
function getStyle(obj, attr)
{
 if(obj.currentStyle){
 return obj.currentStyle[attr]; 
 }else{
 return getComputedStyle(obj, false)[attr];
 }
}
function startMove(obj, json, fn)
{
 clearInterval(obj.timer);
 obj.timer = setInterval(function(){
 var bStop = true;
 for(var attr in json){
  var iCur = 0;
  if(attr == 'opacity'){
  iCur = Math.round(parseFloat(getStyle(obj, attr))*100);
  }else{
  iCur = parseInt(getStyle(obj, attr));
  }
  var iSpeed = (json[attr] - iCur)/8;
  iSpeed = iSpeed>0?Math.ceil(iSpeed):Math.floor(iSpeed);
  if(iCur != json[attr]){
  bStop = false;
  }  
  if(attr == 'opacity'){
  obj.style.filter = 'alpha(opacity='+(iCur+iSpeed)+')';
  obj.style.opacity = (iCur+iSpeed)/100;
  }else{
  obj.style[attr] = iCur + iSpeed + 'px';
  }  
 }
 if(bStop){
  clearInterval(obj.timer);
  if(fn){
  fn();
  }
 }
 }, 30);
}
</script>
</head>
<body>
<input id="btn1" type="button" value="运动"/>
<div id="div1"></div>
</body>
</html>