Trouble with window.onBeforeUnload when compiled to Javascript

[Thomas Løcke]

Hi all,

I'm having some problems getting window.onBeforeUnload to work when compiled to JS.

It works just fine in Dartium, but neither Chrome nor Firefox seems to care.

The code is dead simple:

void main() {

  window.onBeforeUnload.listen((_) {

    return 'foo';

  }); 

}

In Dartium that pops a neat little box when trying to either refresh the page or close the page.

Compiled to JS I get nothing: The page just refresh or close without warning.

Have I stumbled on a dart2js bug, or am I missing something?

:o)

Thomas

[Günter Zöchbauer]

I think this is just a onBeforeUnload problem. See http://stackoverflow.com/questions/9626059, http://stackoverflow.com/questions/276660

[Thomas Løcke]

Well yes, but isn't that then ultimately a dart2js problem, seeing as the code works perfect in Dartium?

[Rasmus Eneman]

The thing is, streams doesn't know about the listeners return value.
According to very old code (nearly a year) there is a returnValue setter on the passed event object which the message should be set to.
Kind of strange it works in Dartium though :/

[Alan Knight]

Yes, I think you set should set the returnValue on the event to have that used. I don't know why it would work in Dartium, there isn't anything obvious in the code, but I suspect we'll fix that glitch :-)

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[Thomas Løcke]

Hi Rasmus,

Den mandag den 4. maj 2015 kl. 18.05.27 UTC+2 skrev Rasmus Eneman:

The thing is, streams doesn't know about the listeners return value.
According to very old code (nearly a year) there is a returnValue setter on the passed event object which the message should be set to.
Kind of strange it works in Dartium though :/

You are the man Rasmus! Thanks a bunch. I changed the type from plain Event to BeforeUnloadEvent and BAM! then I had event.returnValue available. Setting that fixed it. It now works both in Dartium and when compiled to JS.

Why it worked before in Dartium: I have no idea.