W3C home > Mailing lists > Public > www-dom@w3.org > January to March 2012

Re: [DOM4] EventTarget as first class citizen

From: Marcos Caceres <w3c@marcosc.com>
Date: Mon, 27 Feb 2012 14:18:55 +0000
To: Jonas Sicking <jonas@sicking.cc>
Cc: www-dom@w3.org
Message-ID: <5A15B03EBCFA4230B85FA016612D7236@marcosc.com>
(moving to DOM list, from WebApps list...)


On Thursday, February 23, 2012 at 3:18 PM, Jonas Sicking wrote:

> On Thu, Feb 23, 2012 at 12:21 PM, Marcos Caceres <w3c@marcosc.com (mailto: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.  

It would be great to see something like the above.   
Received on Monday, 27 February 2012 14:19:31 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Friday, 22 June 2012 06:14:09 GMT