When a chrome app window is closed, is it possible to detect the event? and do an action before the window is closed?
Vincent's answer will work in some cases, but the documentation warns that some chrome api functionality will be lost by the time the onClosed event is fired.
Note, this should be listened to from a window other than the window being closed, for example from the background page
To listen for this event from the background page, do something like this:
chrome.app.window.get(windowIDUsedToCreateChildWindow).onClosed.addListener(function(){...})
chrome.app.window.current().onClosed allows you to register an event listener for when a window is closed.