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                        /JavaScript進(jìn)階篇

代碼問題求指教，一大堆bug

<!DOCTYPE?html>
<html>
<head?lang="en">
????<meta?charset="UTF-8">
????<title>瀏覽器對(duì)象</title>
</head>
<body>
????<h3>操作成功</h3>
????<b?id="second">5</b>秒后回到主頁面&nbsp;<a?href="javasript:goback();">返回</a>
????<script?type="text/javascript">
????????var?i?=?5;
????????var?sec?=?document.getElementById("second");
????????function?sec(){
????????????i--;
????????????sec.innerHTML=i;
????????????if(i==1){
???????????????location.;
????????????}
????????????setTimeout("sec()",1000);
????????}
???????sec();
????????function?goback(){
????????????window.history.back();
????????}
????</script>
</body>
</html>

當(dāng)把var sec 定義在sec()函數(shù)外面時(shí)，執(zhí)行出錯(cuò)

<!DOCTYPE?html>
<html>
<head?lang="en">
????<meta?charset="UTF-8">
????<title>瀏覽器對(duì)象</title>
</head>
<body>
????<h3>操作成功</h3>
????<b?id="second">5</b>秒后回到主頁面&nbsp;<a?href="javasript:goback();">返回</a>
????<script?type="text/javascript">
????????var?i?=?5;
????????function?sec(){
????????????var?sec?=?document.getElementById("second");
????????????i--;
????????????sec.innerHTML=i;
????????????if(i==1){
???????????????location.;
????????????}
????????????setTimeout("sec()",1000);
????????}
???????sec();
????????function?goback(){
????????????window.history.back();
????????}
????</script>
</body>
</html>

而定義在sec()里面就沒有問題了。。。有點(diǎn)想不明白是什么原因

還有，我發(fā)現(xiàn)如果網(wǎng)速比較慢的話，秒數(shù)會(huì)一直讀到負(fù)數(shù)直到打開網(wǎng)頁，不知道有沒有什么解決辦法。

用firefox瀏覽器，點(diǎn)擊返回總是提示：Firefox 不知道如何打開這個(gè)地址，因?yàn)閰f(xié)議 (javasript) 未與任何程序關(guān)聯(lián)，或者不允許在這種情況下進(jìn)行。這是什么原因呢？

請(qǐng)教大家！謝謝！