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

函数外的var alpha=30;是变化的吗！和if语句里面的alpha应该不是一个值，动态还是固定的，为什么？

<!DOCTYPE HTML>
<html lang="en/zh">
<head>
    <meta charset="UTF-8">
    <title>JS_透明度动画</title>
    <style type="text/css">
        *{
            padding: 0px;
            margin: 0px;            
        }
        #div1{
            width: 200px;
            height: 200px;
            background: red;    
            filter:alpha(opacity:30);    /*ie低版本不支持opacity的  只支持filter */    
            opacity: 0.3;    /*firefox,chrome*/
        }
    </style>
    <script type="text/javascript">
        window.onload=function(){
            var oDiv=document.getElementById("div1");
            oDiv.onmouseover=function(){
                changeOpcity(100);
            }
            oDiv.onmouseout=function(){
                changeOpcity(30);
            }
        }

        var timer=null;
        var alpha =30;
        function changeOpcity(target){
            var oDiv=document.getElementById("div1");
            clearInterval(timer);
            timer=setInterval(function(){
                var speed = 0;
                if(alpha>target){
                    speed=-10;
                }else{
                    speed=10;
                }

                if(alpha==target){
                    clearInterval(timer);
                }else{
                    alpha+=speed;
                    oDiv.style.filter='alpha(opacity:'+alpha+')';/*IE*/
                    oDiv.style.opacity=alpha/100;
                }
            },30);
        }
    </script>
</head>
<body>
    <div id="div1">
    
    </div>
</body>
</html>