Allowing Window.onBeforeUnload event to work properly.

Allowing Window.onBeforeUnload event to work properly.

There are a couple of issues here, fixing some of them, but not quite all.

Background- the beforeunload event is used to present a dialog to the user after they have clicked a window/tab close button, usually to indicate unsaved changes. This is effectively the only mechanism available to preempt the close action.

In WebKit, the user must return a string value from the beforeunload event and that string will be displayed in an alert dialog prompting the user if they are sure they want to leave the page.

In FireFox, IE & the W3C spec, the beforeunload event is of type BeforeUnloadEvent. The string used to prompt the user is specified by the 'returnValue' field. Furthermore, WebKit exposes 'returnValue' as a bool on Event, where the spec does not have it on Event at all.

With this change, a user can utilize the beforeunload event on all platforms:
  window.onBeforeUnload.listen((e) {
    e.returnValue = "foo!";
  });


BUG=2350
Committed: https://code.google.com/p/dart/source/detail?r=21003

[ngeoffray, 2013-02-12 21:52:00]

dart2js changes LGTM

[Anton Muhin, 2013-02-13 08:03:01]

Pete, have you checked if Dartium works fine with this change?

If yes, LGTM.  If no, is there anything I can help you with?

[blois, 2013-02-13 21:01:25]

On 2013/02/13 08:03:01, Anton Muhin wrote:
> Pete, have you checked if Dartium works fine with this change?
> 
> If yes, LGTM.  If no, is there anything I can help you with?

Fails to compile DartEvent.cpp, imagine it needs some magic. Would you be able
to take a look Anton?

Thanks!

[sra1, 2013-02-13 21:36:21]

lgtm with @Creates

https://codereview.chromium.org/12218111/diff/6/sdk/lib/html/dart2js/html_dar...
File sdk/lib/html/dart2js/html_dart2js.dart (right):

https://codereview.chromium.org/12218111/diff/6/sdk/lib/html/dart2js/html_dar...
sdk/lib/html/dart2js/html_dart2js.dart:10439: +  Object returnValue;
This needs a @Creates annotation to indicate that reading it does not create
instances of all native types.
Use @Creates('Null'), that is what is used elsewhere.

[blois, 2013-04-04 22:33:03]

Sorry, this was on the back-burner for a while, updated the CL, incorporating
Anton's feedback & it now works the same on all browsers and on Dartium
(hooray).

The core EventListener changes are the same from the last CL, but I've
refactored the Event API-

Basically Event is not supposed to have a returnValue field, in the W3C spec
this is on a BeforeUnloadEvent class, which WebKit does not have.

Changes:
Removed Event.returnValue
Added a new BeforeUnloadEvent which implements Event and adds returnValue
Added a _WrappedEvent helper class to make it easier to wrap events, shared this
with the KeyEvent code
Made a special stream for window.beforeunload that converts from Event to the
custom BeforeUnloadEvent and returns the returnValue to the browser.
For all browsers, you now only need to set the returnValue field

[Emily Fortuna, 2013-04-04 23:35:46]

lgtm

[sra1, 2013-04-05 22:23:11]

lgtm

[blois, 2013-04-05 22:30:40]

Committed patchset #3 manually as r21003 (presubmit successful).