This comment was originally written by andi...@gmail.com

With the help of stackoverflow the current workaround looks like this:

var jsOnMessageEvent = context['chrome']['runtime']['onMessage'];
JsObject dartOnMessageEvent = (jsOnMessageEvent is JsObject ? jsOnMessageEvent : new JsObject.fromBrowserObject(jsOnMessageEvent));
dartOnMessageEvent.callMethod('addListener', [onMessageListener]);

Ofcourse this dosen't fix the bug, but might be useful to know for fixing it.

CC Justin

cc @justinfagnani.
Added Area-Dart2JS, Triaged labels.

What type of object is returned from context['chrome']['runtime']['onMessage'] in dart2js?

This comment was originally written by andi...@gmail.com

The type is called "Event"

I don't know enough about the Chrome APIs, but that seems odd. I would expect onMessage to be some kind of event provider, not an Event itself.

dart:js in dart2js simply performs an "is Event" check to decide if the Dart object should be returned rather than a wrapper. That check is returning true, so I would assert that dart:js/dart2js is working correctly, and one of the following is the real bug:

1. chrome.runtime.onMessage shouldn't be an Event object. This is out of our scope though.
2. dart2js isn't implementing "is Event" correctly, and it should return false.
3. Dartium isn't implementing "is Event" correctly, and it should return true, or similarly Dartium isn't performing the Event type check properly.

Adding Emily and Jacob who can comment on (2) and (3).

cc @jacob314.
cc @efortuna.

ping.

I think this is a chrome library bug and not a dart2js bug -- we see similar problems with dart:html when we haven't correctly matched up the underlying JS prototype to the Dart version. I'll do some quick research on this API as I'm much less familiar with the Chrome APIs, but I think this is the direction of the bug.

What is the type of the object you get when you access chrome.runtime.onMessage in regular JS? That method isn't showing up in my JS console, but I suspect I'm "doing it wrong" as I have not worked with Chrome extensions until now.

This comment was originally written by andi...@gmail.com

I think only chrome extensions and apps have access to the chrome api.
Using native js "console.log(chrome.runtime.onMessage)" prints the following:

Event {addListener: function, removeListener: function, hasListener: function, hasListeners: function, dispatchToListener: function…}proto: Event

Hm... That definitely makes it seem like option #­1 (bug in the API itself) is the culprit. Is the regular JS return type (not involving Dart at all) of any of the other chrome EventHandlers an "Event"? Like chrome.alarms.onAlarm, or chrome.declarativeWebRequest.onRequest, or chrome.webNavigation.onCommitted?

This comment was originally written by andi...@gmail.com

Have tested for chrome.alarms.onAlarm and chrome.declarativeWebRequest.onRequest. They both return also an Event-object.

So it would seem the Chrome API version of Event is a little different from the standard DOM Event...

Honestly, this prototype organization seems a little crazy to me.

I wonder, is it the same Event prototype as regular DOM events?

Is

Object.getPrototypeOf(chrome.runtime.onMessage) === window.Event.prototype

true?

This comment was originally written by andi...@gmail.com

Good morning.

Object.getPrototypeOf(chrome.runtime.onMessage) === window.Event.prototype is false.

This comment was originally written by andig...@gmail.com

I did some research. Looks like chrome api has it's own Event-type:

https://developer.chrome.com/extensions/events#type-Event

Indeed, so the Chrome APIs have their own wacky Event type, then (confusing!). So this suggests it's maybe a problem with dart2js -- perhaps it sees "Event" and is incorrectly mapping it to the dart:html Event?

cc @rakudrama.

FYI - Stephen is on vacation through 9/22

Yes, sounds like a dart2js/dart:html bug.

Thanks for your help investigating this Andi.