Re: [webcomponents] Need "slotting changed" event (#288)

Having worked with Shadow DOM a lot, not having this feature in Chrome's existing implementation is very cumbersome. I'd *really* like to see this api included in *v1* if possible.

If it's ever important to be able to manage your children (menu, tabs, stack of pages, carousel, etc), then you need to know when the elements distributed to your slots have changed. 

MutationObservers are quite cumbersome to use for this: To use MO, you have to do something like: (1) MO your own childList, (2) whenever a slot is added to you, (3) find that slot's host element (recurse up the tree to find the shadowRoot.host) and MO that host's childList, and (4) repeat step 2 for that element. This is just to see childList changes. To get the actual distribution changes to a given slot, you have to observe attributes on every one of these children and then, perhaps, do a dirty checking scheme to detect what the changes are.

The platform has all this information as a result of distributing. For the user to do this correctly is both complicated and requires significant duplication of effort.

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/webcomponents/issues/288#issuecomment-124245078