有关卸载事件
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>卸载事件</title>
<script type = "text/JavaScript">
window.open("http://www.imooc.com","_self");
window.onunload = onunload_message;
function onunload_message(){
confirm("你确定要离开此网页么？");
}
</script>
</head>
<body>
</body>
</html>打开网页（慕课网）后刷新怎么不会执行卸载事件呢？问题在哪儿？怎么解决啊？谢谢大家了
