                        课程
                    
                        /前端开发
                        
                            /JavaScript
                        
                        /网页广告特效

关于else问题

<!doctype html>
<html>
<head>
    <meta charset="UTF-8">
    <title>顶部广告展开收起</title>
    <style>
        body, div, img, span {
            margin: 0;
            padding: 0;
        }
        #content {
            width: 960px;
            height: 1000px;
            background: #ccc;
            margin: 0 auto;
        }
        #ad {
            width: 960px;
            margin: 0 auto;
            display: none;
            position: relative;
            overflow: hidden;
        }
        #close {
            position: absolute;
            width: 20px;
            height: 20px;
            text-align: center;
            line-height: 20px;
            background: #CF3;
            top: 0;
            right: 0;
            display: none;
            cursor: pointer;
        }
    </style>
</head>
<body>
<div id="ad">
    <img id="adcon" src="ad.png" width="960" height="385"/>
</div>
<div id="content"><img src="数字商品-10-23.jpg" /></div>
<script>
    var $ = function(id){
        return document.getElementById(id);
    };
    var oAd = $("ad");
    var oAdcon =$("adcon");
    var h = 0;
    var maxH = oAdcon.height;
    function adDown(){
        if(h<maxH){
            h+=5;
            oAd.style.height = h+"px";
            oAd.style.display = "block";
            setTimeout(adDown,10)
        }else{
            oAd.style.height = h+"px";
            oAd.style.display = "block";
        }
    }
    setTimeout(adDown,3000)
</script>
</body>
</html>


我想问一下，else加不加没什么变化。为什么要加进去？