Onunload，onbeforeunload都是在刷新或关闭时调用
<script language=javascript>
window.onbeforeunload = onbeforeunload_handler;
window.onunload = onunload_handler;
//准备去加载
function onbeforeunload_handler(){
var warning="确认退出?";
return warning;
}
//加载回来准备更换页面内容
function onunload_handler(){
var warning="谢谢光临";
alert(warning);
}

</script>