Detecting if the user closes the WebDialog with the [x] button

[DanRathbun]

No mention is made of detecting if the user closes the WebDialog with the [x] button.

I seem to remember a topic thread at SketchUcation on this, but a search does not find it easily.

So, I opened a thread in the new discourse forums ...
Detecting the exit button click in a browser dialog’s JavaScript

I tried everything suggested on StackOverflow, but nothing worked. I used addEventListener, attachEvent, just plain window.onclose =, and even JQuery's $(window).on("close"....

I also tried the unload and the beforeunload events. Nothing was firing for me (in SU2016 specifically, although another member said it was firing in SU2014.)

I finally gave up, and used a Ruby-side set_on_close block as explained in post 9 of the topic thread mentioned above.