title: Ionic run function before app closes
body: <p>Is there some kind of function that I can call that listens to whether the app is about to exit, or close or go into the background.. Basically any event that means "the user has stopped using the app"?</p>
  
  <p>I'm my app I build up a 'user log' that tracks the user as they are navigating through the app. Instead of sending little pieces of data constantly to the server as these events occur, I want to send off the whole batch in one go just before the user stops using the app (again, whether that means closing the app completely, sending it to the background etc.)</p>
  
  <p>And lastly, if such a function does indeed exist.. where do you put that function? In your <code>app.js</code>? Or do you have to put that listener in every single controller of your app?</p>