                        課程
                    
                        /前端開發(fā)
                        
                            /JavaScript
                        
                        /網(wǎng)頁廣告特效

關(guān)于else問題

<!doctype?html>
<html>
<head>
????<meta?charset="UTF-8">
????<title>頂部廣告展開收起</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="數(shù)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>


我想問一下，else加不加沒什么變化。為什么要加進(jìn)去？