add source to the dispatched events

[UweOhse]

This adds the source to the interest and loseinterest events.

[keithamus]

We need to crate an InterestEvent which subclasses Event, and both of these events should use that.

.source is also readonly, so you need to make it a getter and not a setter. You'll also want to retarget source so you don't expose ShadowDOMs.

All together this will look something like:

function getRootNode(node) {
  if (node && typeof node.getRootNode === "function") {
    return node.getRootNode();
  }
  if (node && node.parentNode) return getRootNode(node.parentNode);
  return node;
}
const eventSourceElements = new WeakMap();
class InterestEvent extends Event {
  constructor(type, eventInit = {}) {
    super(type, eventInit);
    const { source } = eventInit;
    if (source != null && !(source instanceof Element)) {
      throw new TypeError(`source must be an element`);
    }
    eventSourceElements.set(this, source || null);
  }

  get [Symbol.toStringTag]() {
    return "InterestEvent";
  }

  get source() {
    if (!eventSourceElements.has(this)) {
      throw new TypeError("illegal invocation");
    }
    const source = eventSourceElements.get(this);
    if (!(source instanceof Element)) return null;
    // Retarget `source` to the current event's root:
    const sourceRoot = getRootNode(source);
    if (sourceRoot !== getRootNode(this.target || document)) {
      return sourceRoot.host;
    }
    return source;
  }
}

In addition, the event is cancelable, and so we need to return early if it's preventdefaulted. We can check dispatchEvent's return value for this.

So each of the dispatch callsites become:

Suggested change

	let evt = new Event(interestEventName);
	evt.source = invoker
	target.dispatchEvent(evt);
	const shouldContinue = target.dispatchEvent(new InterestEvent(interestEventName, { source: invoker }));
	if (!shouldContinue) return;

[mfreed7]

Thanks for reviewing this Keith!

[aliu-vmware]

Pretty interested in getting this in. One thing I'm curious about, is the WeakMap really necessary for some reason, or can it be replaced by a private element?

[mfreed7]

Pretty interested in getting this in.

I think it's just waiting on a response from Keith's review comments.

[aliu-vmware]

Pretty interested in getting this in.

I think it's just waiting on a response from Keith's review comments.

I'd like to be respectful, but it's been over a month with no response. What's a reasonable time to wait before I submit a PR with the changes included?

[mfreed7]

Pretty interested in getting this in.

I think it's just waiting on a response from Keith's review comments.

I'd like to be respectful, but it's been over a month with no response. What's a reasonable time to wait before I submit a PR with the changes included?

I think a month is reasonable. If you'd like to put up a PR with the comments incorporated, we could definitely take a look.