Is there a way to capture the “closing” event in an iBook widget?

I have widgets that work in iBook. In particular, they play music and sounds, as well as the “main loop” of Javascript.

I want sound and music to stop whenever the widget is closed by the user. I don’t know if there is any FocusLost or WidgetClosed event raised by the iBook.

In my current understanding, this use case does not launch “onunload”, because this one will be launched whenever the iPhone decides to return some memory, because it needs it for the page that the user is currently on.

What is the standard solution to this problem?