倒计时没有用，还有就是innerHTML和value的区别
<!DOCTYPE html>
<html>
<head>
<title>浏览器对象</title>
<meta http-equiv="Content-Type" content="text/html; charset=gkb"/>
</head>
<body>
<!--先编写好网页布局-->
<h1>操作成功</h1>
<p><span id="num">5</span>秒后回到主页<a href="javascript:window.history.go(-1)">返回</a></p>
<script type="text/javascript">
var b=5;
function zhuan(){
document.getElementById('num').innerHTML = b;
b--;
if(b == 0)
location.href('http://www.imooc.com');
setTimeout("zhuan()",1000);
}
</script>
</body>
</html>
