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Re: [DOM4] EventTarget as first class citizen

From: Jonas Sicking <jonas@sicking.cc>
Date: Thu, 23 Feb 2012 16:18:30 +0100
Message-ID: <CA+c2ei_Tc7ZhOWq=X0HwznRY3qrE4icenKAtfZBGgP-64cfaEA@mail.gmail.com>
To: Marcos Caceres <w3c@marcosc.com>
Cc: public-webapps <public-webapps@w3.org>
On Thu, Feb 23, 2012 at 12:21 PM, Marcos Caceres <w3c@marcosc.com> wrote:
> Hi,
> Would it be possible for DOM4 to define a way for user objects to be able to extend EventTarget (as in Object.create(EventTarget))?
>
>
>
> The use case: give the ability to create objects that can dispatch events using native means… instead of hacking around it like so:
>
> var obj = Object.create(null);
> var dispatcher = document.createElement("x-EventDispatcher");
>
> //implement EventTarget interface on obj
> Object.defineProperty(obj, "addEventListener", {
> value: function(type, callback, capture){
> dispatcher.addEventListener(type, callback, capture);
> }
> });
>
> Object.defineProperty(obj, "removeEventListener", {
> value: function(type, callback, capture){
> dispatcher.removeEventListener(type, callback, capture);
> }
> });
>
> Object.defineProperty(obj, "dispatchEvent", {
> value: function(e){
> dispatcher.dispatchEvent(e);
> }
> });
>
>
>
> var e = document.createEvent('CustomEvent');
> e.initEvent("myEvent", false, false, null);
> dispatcher.dispatchEvent(e);
>
>
>
> Also, AFAIK, all JS frameworks have implemented custom ways of handling events and how they are dispatched, so clearly its a desired part of the platform. For example:
>
> http://developer.yahoo.com/yui/docs/YAHOO.util.CustomEvent.html
> http://api.jquery.com/category/events/event-object/
> http://dojotoolkit.org/reference-guide/quickstart/events.html
>
> Developers have also built their own:
> http://www.nczonline.net/blog/2010/03/09/custom-events-in-javascript/
>
> Other solutions fire at the document, which means registering listeners on an object that is not the one that needs to receive the event:
> http://tiffanybbrown.com/2011/10/12/dispatching-custom-dom-events/
>
> So, together with CustomEvents provided by the platform, it would be nice to have a custom EventTarget to fire those things at :)

I think the way we should do this is to enable instantiating
EventTarget objects using an EventTarget ctor. This won't give you a
neato extension syntax, but I think we'll have to rely on ES.next for
that. Before ecma-script has a better solution you can always
monkeypatch the object.

So something like:
a = new EventTarget();
b = new EventTarget(a); // a is the parent in the target chain

should be doable. I don't know if we need a way to modify the parent
chain after construction. It's somewhat complex to allow this while
still preventing cycles from being created.

/ Jonas
Received on Thursday, 23 February 2012 15:19:28 GMT

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