请看看我这个怎么回事？
<!DOCTYPE HTML>
<html>
<head>
<script>
var sum=5;
function acc(){
document.getElementById("con").value=sum;
if(sum=0){
window.history.go(-1);
}
sum=sum-1;
var i=setInterval("acc()",1000);
}
function abb(){
window.history.back();
}
</script>
</head>
<body>
<h1>操作成功</h1><br />
<input type="text" id="con" value=5> <h2>秒后回到主页</h2><input type="button" value="返回" onclick="abb()" />
</body>
</html>
