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Re: Callback when an event handler has been added to a custom element

From: Olli Pettay <olli@pettay.fi>
Date: Fri, 6 Nov 2015 22:44:21 +0200
To: Justin Fagnani <justinfagnani@google.com>, Travis Leithead <travis.leithead@microsoft.com>
Cc: Mitar <mmitar@gmail.com>, public-webapps <public-webapps@w3.org>
Message-ID: <563D1125.7090808@pettay.fi>
On 11/06/2015 09:28 PM, Justin Fagnani wrote:
> You can also override addEventListener/removeEventListener on your element. My concern with that, and possibly an event listener change callback, is
> that it only works reliably for non-bubbling events.
How even with those? One could just add capturing event listener higher up in the tree.
You need to override addEventListener on EventTarget, and also relevant onfoo EventHandler setters on Window and Document and *Element prototypes,
but unfortunately even that doesn't catch onfoo content attributes (<div onclick="doSomething">). But one could use MutationObserver then to
observe changes to DOM.


> On Thu, Nov 5, 2015 at 4:16 PM, Travis Leithead <travis.leithead@microsoft.com <mailto:travis.leithead@microsoft.com>> wrote:
>     Interesting. Alternatively, you can add .onwhatever handlers, as well as define your own overload of addEventListener (which will be called
>     instead of the EventTarget.addEventListener method). That way you can capture all attempts at setting events on your element.
>     -----Original Message-----
>     From: Mitar [mailto:mmitar@gmail.com <mailto:mmitar@gmail.com>]
>     Sent: Thursday, November 5, 2015 4:05 PM
>     To: public-webapps <public-webapps@w3.org <mailto:public-webapps@w3.org>>
>     Subject: Callback when an event handler has been added to a custom element
>     Hi!
>     We are using message ports to communicate with our logic and are wrapping the API into a custom element. The issue is that we would like to call
>     start on a message port only after user has registered an event handler on the custom element instance. But it seems there is no way to get a
>     callback when an event handler is added.
>     So I am suggesting that there should be a callback every time an event listener is added to a custom element (and possibly one when removed).
>     Mitar
>     --
>     http://mitar.tnode.com/
>     https://twitter.com/mitar_m
Received on Friday, 6 November 2015 20:44:54 UTC

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