Dispatch slotchange event #1084
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The first time a `slotchange` event is registered, we setup a SlotChangeMonitor
on the page. This uses a global (ugh) MutationEvent to detect slot changes.
We could improve the perfomance of this by installing a MutationEvent per
custom element, but a global is obviously a lot easier.
Our MutationEvent currently fired _during_ the changes. This is problematic
(in general, but specifically for slotchange). You can image something like:
```
slot.addEventListener('slotchange', () => {
// do something with slot.assignedNodes()
});
```
But, if we dispatch the `slotchange` during the MutationEvent, assignedNodes
will return old nodes. So, our SlotChangeMonitor uses the page scheduler to
schedule dispatches on the next tick.
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The first time a
slotchangeevent is registered, we setup a SlotChangeMonitor on the page. This uses a global (ugh) MutationEvent to detect slot changes.We could improve the perfomance of this by installing a MutationEvent per custom element, but a global is obviously a lot easier.
Our MutationEvent currently fired during the changes. This is problematic (in general, but specifically for slotchange). You can image something like:
But, if we dispatch the
slotchangeduring the MutationEvent, assignedNodes will return old nodes. So, our SlotChangeMonitor uses the page scheduler to schedule dispatches on the next tick.