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                        課程
                    
                        /前端開發(fā)
                        
                            /JavaScript
                        
                        /展開與收起效果

讓我來完善下

<!DOCTYPE?HTML>
<html>
<head>
<meta?charset="utf-8"/>
<meta?http-equiv="pragma"?content="no-cache">

<title>展開與收起特效</title>
<style>
body{
margin:?0?auto;
padding:?0px;
}
#pn{
background:?#e8e8e8;
width:?950px;
display:?block;
margin:?0?auto;
padding:?5px;
height:?auto;
text-align:?center;
position:relative;
z-index:?1;
overflow:?hidden;
}
.content{
margin:0?auto;
padding:10px;
width:950px;
background:?gray;
text-align:?center;
height:40px;
color:#fff;
position:?relative;
z-index:2;
}

</style>
</head>
<body>

<div?id="pn">
<h1>歡迎來到英雄聯(lián)盟</h1>
<h1>大幅廣告</h1>
</div>
<div>
敵軍還有30S到達(dá)戰(zhàn)場(chǎng)，碾碎他們
<br>
正文
</div>

<script>
var?h?=?0;
function?addH(){
if(h?<?300){
h?+=?5;
document.getElementById("pn").style.height?=?h?+?"px";
}?else?{
return;
}
setTimeout(addH,?30);
}
function?subH(){
if(h?>?0){
h?-=?5;
document.getElementById("pn").style.height?=?h?+?"px";
}?else?{
document.getElementById("pn").style.display?=?'none';
return;
}
setTimeout(subH,?30);
}
window.onload?=?function(){
addH();
setTimeout(subH,?5000);
}
</script>
</body>
</html>