HTML DOM closed 属性
HTML DOM Window 对象参考手册定义和用法
closed 属性可返回一个布尔值，该值声明了窗口是否已经关闭。该属性为只读。
当浏览器窗口关闭时，表示该窗口的 Windows 对象并不会消失，它将继续存在，不过它的 closed 属性将设置为 true。
语法
window.closed
实例
下面的例子可检测新窗口是否已被关闭：
<html>
<head>
<script type="text/javascript">
function ifClosed()
{
document.write("'myWindow' has been closed!")
}
function ifNotClosed()
{
document.write("'myWindow' has not been closed!")
}
function checkWin()
{
if (myWindow.closed)
ifClosed()
else
ifNotClosed()
}
</script>
</head>
<body>
<script type="text/javascript">
myWindow=window.open('','','width=200,height=100')
myWindow.document.write("This is 'myWindow'")
</script>
<input type="button" value="Has 'myWindow' been closed?"
onclick="checkWin()">
</body>
</html>