js 渐变运动框架

<!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=gb2312" />
<title>无标题文档</title>
<style>
div{width:100px;height:100px;background:red;filter:alpha(opacity=100);opacity:1;}
</style>
<script>
    function getStyle(obj,attr){
        return obj.currentStyle ? obj.currentStyle[attr]:getComputedStyle(obj)[attr];
    }
    function startMove(obj,attr,target,fn){
        clearInterval(obj.timer);
        obj.timer = setInterval(function(){
            if(attr == 'opacity'){
                var iCur = parseInt(parseFloat(getStyle(obj,attr))*100);

            }else{
                var iCur = parseInt(getStyle(obj,attr));
            }
            var speed = (target-iCur)/8;
            speed = speed >0 ? Math.ceil(speed):Math.floor(speed);
            if(iCur == target){
                clearInterval(obj.timer);
                fn && fn();
            }else{
                if(attr == 'opacity'){
                    
                    obj.style.filter = 'alpha(opacity='+(iCur+speed)+');';
                    obj.style[attr] = (iCur+speed)/100;
                }else{
                    obj.style[attr] = iCur+speed+'px';
                }
                
            }    
        },30);
        
    }
    window.onload = function(){
        var arrInput = document.getElementsByTagName('input')[0];
        var arrDiv = document.getElementsByTagName('div')[0];
        arrInput.onclick = function(){
            startMove(arrDiv,'width',300,function(){
                startMove(arrDiv,'height',300,function(){
                    startMove(arrDiv,'opacity',30);
                });
            });
        };
    };
    
    
    
</script>
</head>

<body>
<input type='button' value = '开始运动'/>
<div></div>
</body>
</html>