javascript动画效果类封装代码

<input id=output3 style="position:absolute;top:300;left:300;"/>
<input id=output1 />
<input id=output2 />
<br/>
<input id=output4 />

<script>
function Animation(target,targetProperty,closure,precision)
{
  closure=closure||function(x){return x;};
  precision=precision||10;
  this.handle;

  var beginTime=new Date();
  var stopTime=new Date();
  this.Begin=function(){
    beginTime=new Date();
    this.handle=setInterval(
      function(){
        var now=new Date();
        target[targetProperty]=closure(now.getTime()-beginTime.getTime());
      },
      precision
    );
       }

  this.Continue=function(){
    var now=new Date();
    beginTime.setTime(now.getTime()-stopTime.getTime()+beginTime.getTime());

    this.handle=setInterval(
      function(){
        var now=new Date();
        target[targetProperty]=closure(now.getTime()-beginTime.getTime());
      },
      precision
    );
  }

  this.Stop=function(duration){

    clearInterval(this.handle);

    if(duration===undefined)
    {
      stopTime=new Date();
      duration=stopTime.getTime()-beginTime.getTime();
    }
    else stopTime.setTime(beginTime.getTime()+duration)
    target[targetProperty]=closure(duration);
  }
}

function StoryBoard(Duration,onfinish,flag)
{
  onfinish=onfinish||function(){};
  var r=new Array();
  r.appendAnimation=function(animation)
  {
    if(animation instanceof Animation)
      this.push(animation);
  }
  r.removeAnimation=function(animation)
  {
    for(var i=0;i<r.length;i++)
    {
      if(r[i]==animation)
      {
        r.splice(i,1);
        break;
      }
    }
  }
  r.start=function(){    
    for(var i=0;i<r.length;i++)
    {
      r[i].Begin();
    }
    setTimeout(
      function(){
        for(var i=0;i<r.length;i++)
        {
          r[i].Stop(Duration);
        }
      },
      Duration
    );
    onfinish();
  }
  return r;

}
//////////////////////////////下面是使用方法////////////////////////////////
function $(id)
{
   return document.getElementById(id);
}
var a1=new Animation($("output1"),"value");
var a2=new Animation($("output2"),"width",function(x){return Math.floor(x/10);});
var a3=new Animation($("output3").style,"filter",function(x){return "alpha(opacity="+Math.floor(x/5000*100)+")";});
var a4=new Animation($("output4").style,"width",function(x){return Math.floor(x*x*x/50000/5000)+"px";});
var s=new StoryBoard(5000);
s.appendAnimation(a1);
s.appendAnimation(a2);
s.appendAnimation(a3);
s.appendAnimation(a4);
s.start();

</script>
<pre>
output1是改变value
output1是改变宽度
output3是淡入
output4是带缓动的宽度
</pre>