how to identify onbeforeunload was caused by clicking close button

Question

How do I determine if onbeforeunload was caused by clicking the close button or a page refresh or generally what event caused onbeforeunload?

here is a snippet:

Answer 1

As far as I know, there is no way of determining what caused the onbeforeunload. The event is triggered when window is about to close whether closing the browser or some other way.