On Dec 9, 2013, at 11:13 AM, Scott Miles <sjmi...@google.com> wrote:
> Domenic Denicola a few messages back gave a highly cogent explanation of the
> exact line of thinking arrived at last time we went through all this
> material.
>
> I'm not wont to try to summarize it here, since he said it already better
> there. Perhaps the short version is: nobody knows what the 'standard use
> case' is yet.
>
> In previous adjudications, the straw that broke that camel's back was with
> respect to handling auto-generation with inheritance. Shadow-roots may need
> to be generated for each entry in the inheritance chain. Having the system
> perform this task takes it out of the control of the user's code, which
> otherwise has ability to modulate calls to super-class methods and manage
> this process.
>
> class XFoo {
> constructor_or_createdCallback: function() {
> // my shadowRoot was auto-generated
> this.doUsefulStuffLikeDatabinding(this.shadowRoot);
> }
> }
>
> class XBar extends XFoo {
> constructor_or_createdCallback: function() {
> super(); // uh-oh, super call operates on wrong shadowRoot
> }
> }
If the shadow root is optionally automatically generated, it should probably be
passed to the createdCallback (or constructor) rather than made a property
named "shadowRoot". That makes it possible to pass a different shadow root to
the base class than to the derived class, thus solving the problem.
Using an object property named "shadowRoot" would be a bad idea in any case
since it automatically breaks encapsulation. There needs to be a private way to
store the shadow root, either using ES6 symbols, or some new mechanism specific
to custom elements. As it is, there's no way for ES5 custom elements to have
private storage, which seems like a problem. They can't even use the closure
approach, because the constructor is not called and the methods are expected to
be on the prototype. (I guess you could create per-instance copies of the
methods closing over the private data in the created callback, but that would
preclude prototype monkeypatching of the sort built-in HTML elements allow.)
Regards,
Maciej
