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不是上不去就是沒有暫停時間，哪里出問題了？

在火狐里上不去一直抖，????Safari里就沒有暫停時間直接上去了。不知道哪里出問題了。<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
??? <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
??? <title>自動展開</title>
??? <style type="text/css">
??????? body
??????? {
??????????? margin: 0 auto;
??????????? padding: 0;
??????? }
??????? a:focus
??????? {
??????????? outline: none;
??????? }
?????? ?
??????? #pn
??????? {
??????????? background: #e8e8e8;
??????????? height: 120px;
??????????? width: auto;
??????????? display: block;
??????????? margin: 0 auto;
??????????? padding: 5px;
??????????? text-align: center;
??????????? overflow:hidden;
??????? }
??????? .slide
??????? {
??????????? padding: 10px;
??????????? width: 960px;
??????????? margin: 0 auto;
??????????? background: gray;
??????????? text-align: center;
??????????? height: 40px;
??????????? line-height: 40px;
??????????? color: #fff;
??????? }
??? </style>
??? <script type="text/javascript">
?????? var h= 0;
????? ?
??????? //增加高度函數(shù)addH()
?????????? ?
??????? function addh() { ?
?????????? if(h < 300){
?????????????? h += 2;
???????????? document.getElementById("pn").style.height = h + "px";
?????????? }
?? ??? ???? else{
?? ??? ????? return ; ?
?? ??? ???? }
??????????? setTimeout("addh()",30);
??????? }
?????? ?
?????? //網(wǎng)頁加載完畢時，調(diào)用增加高度函數(shù)addH()，等待5秒鐘后調(diào)用減少高度函數(shù)subh()。
??????? window.onload = function(){
??????????? addh();
??????????? setTimeout("subh()",5000);
??????? }
???? ?
???? ?
????? // 減少高度函數(shù)subH()
?? ?
??????? function subh() {
?????????? if(h > 0){
?????????????? h -= 2;
???????????? document.getElementById("pn").style.height = h + "px";
?????????? }
?? ??? ???? else{
?? ??? ????? return? ;
?? ??? ???? }
??????????? setTimeout("subh()",30);
??????? }
??????? ?
?????????? ?
?????????? ?
?????????? ?
??? </script>
</head>
<body>
??? <div id="pn">
??????? <h1>
??????????? 歡迎來到慕課網(wǎng)</h1>
??????? <h2>
??????????? 大幅廣告</h2>
??? </div>
??? <p class="slide">
??????? 慕課網(wǎng)歡迎你</p>
</body>
</html>