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[webcomponents] calling JS on custom element construction

From: Mike Kamermans <nihongo@gmail.com>
Date: Wed, 20 Mar 2013 12:46:16 -0400
Message-ID: <CABhc0+LQh8OY5-TprEqzDe4cOwwvrq75JGnZSNi6pjL_xZMyUw@mail.gmail.com>
To: public-webapps@w3.org
Hey all,

still playing with web components, I was wondering if there's a way to
make a custom element trigger JS whenever an element is built either
through JS calls or when used in the DOM. From the spec, combined with
the toolkitchen polyfills, I can see that the element's <script> block
runs once, when the element gets defined, so I figured I could use an
explicit constructor instead and make things work that way:

var MyCustomElement = function() { console.log("element built"); }

<element name="my-custom-element" constructor="MyCustomElement">

but this does not appear to call the MyCustomElement constructor when
the element is built through the DOM by virtue of just "being used on
a page", and when called on the console with "new MyCustomElement();"
I get the error "TypeError: Object #<HTMLDivElement> has no method
'instantiate'"... If I use "MyCustomElement.prototype = new
HTMLDivElement()" to try to set up a sensible prototype chain, I just
get the error "Uncaught TypeError: Illegal constructor"./

What's the recommended way to set up a custom element that runs some
JS or calls a JS function any time such an element is built for use on
the page?

- Mike "Pomax" Kamermans
Received on Wednesday, 20 March 2013 16:46:44 UTC

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