[flexcoders] Re: Invoking Flex fuction from Javascript for close.window

[Anthony DeBonis]

With ExternalInterface.call you can inject JavaScript into the wrapper 
document.

if ( ExternalInterface.available ) {
                    ExternalInterface.call('alert("TEST")'); 
                        }    
A good example of what your talking about is here thanks to Greg Jessup

http://gregjessup.com/flex-3-catch-browser-exit-or-close-event-using-
javascript-and-externalinterface/