Re: [w3c/webcomponents] How can a custom element detect when it is transcluded into a shadow tree (slotchange)? (#504)

To get around the expensive checks, you could make it so it can only check
and warn in dev so that the expensive checks aren't run in prod code.

On Fri., 2 Dec. 2016, 10:59 Joseph Orbegoso Pea, <notifications@github.com>
wrote:

> It might still be nice for a Custom Element to detect distribution
> (without leaking structure of a shadow root) because then with this
> knowledge it can trigger an event if it needs to. This is not possible with
> slotchange because there's no way for a slot to determine which event a
> distributed node should fire.
>
> After thinking about this for a while, and after successfully making my
> library compatible with ShadowDOM V1 including closed shadow roots
> <https://github.com/trusktr/infamous/issues/40>, I still think the a
> solution to the need described in this issue would be invaluable because
> then I would be able to detect certain conditions that I can not otherwise
> detect without crazy hacks, in order to give the end user of my library
> helpful console messages like "Warning: Your motor-node#someID element does
> not work when distributed to such-an-such element. It must be distributed
> to a motor-scene or motor-node element.`
>
> With slotchange and assignedNodes, I can only detect proper use cases
> where a shadow root is the root of one of my library's custom elements and
> when a slot is child of one of my library's custom elements and when one of
> my library's elements are connected or distributed directly to another
> element of my library. Detecting the other cases would be too hacky and
> expensive so far as I can imagine (involving hijacking attachShadow and
> traversing all shadow roots).
>
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