                        课程
                    
                        /前端开发
                        
                            /JavaScript
                        
                        /JS动画效果

为什么这里设置透明度时用opacity,50而不是用opacity,0.5,在程序第四十步cur=Math.round(parseFloat(getStyle(obj,attr))*100);里不是已经乘了100了吗？

<!DOCTYPE  HTML>
<html >
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>链式运动</title>
<style>
div{width:200px;height:200px;background-color:yellow;margin:10px;float:left;}
</style>
<script type="text/javascript">
   window.onload=function()
    {
     var oDiv1=document.getElementById('div1');
	 
	   oDiv1.onmouseover=function()
	   {
	     startMove(this,'height',400,function()
		 {
		  startMove(oDiv1,'opacity',50);
		 });
	   };
	   oDiv1.onmouseout=function()
	   {
	     startMove(this,'height',200);
	   };
	  
    }
  function getStyle(obj,attr){
     if(obj.currentStyle){
	   return obj.currentStyle[attr];}
	 else{
	   return getComputedStyle(obj,false)[attr];}
  }
  function startMove(obj,attr,iTarget,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=(iTarget-cur)/6;
	 speed=speed>0?Math.ceil(speed):Math.floor(speed);
	    if (cur==iTarget)
		{
		   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=div1></div>
</body>
</html>