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Allow for customisation of the "get the parent" algorithm #1230

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Allow for customisation of the "get the parent" algorithm #1230

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73 changes: 72 additions & 1 deletion dom.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -908,9 +908,14 @@ for historical reasons.
<h3 id=interface-eventtarget>Interface {{EventTarget}}</h3>

<pre class=idl>
[Exposed=*]
interface EventTargetInternals {
attribute EventTarget parent;
};

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This feels a bit cumbersome API, one needs to pass a callback and then use its param to change a property value.

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Would you prefer an init dictionary? One downside to this, as explained in #583 (comment) is that an init dictionary cannot allow setting the parent post-construction.

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Yeah, I suppose we could also do what new Promise() does, but it doesn't seem as extensible:

new EventTarget(setParent => {
  setParent(someParent);
}

I think as long as the capability is only granted to whoever constructed the EventTarget object I'm okay, so alternative proposals welcome.

[Exposed=*]
interface EventTarget {
constructor();
constructor(optional EventTargetCallback cb);

undefined addEventListener(DOMString type, EventListener? callback, optional (AddEventListenerOptions or boolean) options = {});
undefined removeEventListener(DOMString type, EventListener? callback, optional (EventListenerOptions or boolean) options = {});
Expand All @@ -930,6 +935,8 @@ dictionary AddEventListenerOptions : EventListenerOptions {
boolean once = false;
AbortSignal signal;
};

callback EventTargetCallback = undefined (EventTargetInternals internals);
</pre>

<p>An {{EventTarget}} object represents a target to which an <a>event</a> can be <a>dispatched</a>
Expand All @@ -939,6 +946,70 @@ when something has occurred.
<a for=/>list</a> of zero or more <a>event listeners</a>). It is initially the empty list.
<!-- Intentionally not exported. -->

<p>Each {{EventTarget}} object has an associated <dfn for=EventTarget>attached internals</dfn> (null
or an {{EventTargetInternals}} object), initially null.

<p>Each {{EventTargetInternals}} object has an associated <dfn
for=EventTargetInternals>eventTarget</dfn> (an {{EventTarget}} object).

<p>Each {{EventTargetInternals}} object has an associated <dfn
for=EventTargetInternals>parent</dfn> (an {{EventTarget}} object).

<p>The <dfn export for=Event id=concept-eventtarget-constructor>new EventTarget(cb)</dfn> constructor steps are:

<ol>
<li><p>If <var>cb</var> is not null then:

<ol>
<li><p>Let <var>eventTargetInternals</var> a new {{EventTargetInternals}} instance.

<li><p>Set <var>eventTargetInternals</var>'s <a for=EventTargetInternals>eventTarget</a> to
<var>this</var>.

<li><a>Invoke</a> <var>cb</var> with « <var>eventTargetInternals</var> » and with <var>this</var>
as the <a>callback this value</a>.

<li><p>Set <var>this</var>'s <a for="EventTarget">attached internals</a> to
<var>eventTargetInternals</var>.
</ol>
</ol>

<p>The <a for=EventTargetInternals>parent</a> getter steps are to return <var>this</var>'s
<a for=EventTargetInternals>parent</a>.

<p>The <a for=EventTargetInternals>parent</a> setter steps are:

<ol>
<li><p>Let <var>theParent</var> be the given value.

<li><p>Let <var>targets</var> be a new <a for=/>list</a>.

<li>Append <var>this</var>'s <a for=EventTargetInternals>eventTarget</a> to <var>targets</var>.

<li><p>Let <var>parent</var> be <var>theParent</var>.

<li>
<p>While <var>parent</var> is non-null:</p>

<ol>
<li>If <var>targets</var> <a for=set>contains</a> <var>parent</var> then <a>throw</a> a
"{{HierarchyRequestError!!exception}}" {{DOMException}}.

<li>Append <var>parent</var> to <var>targets</var>.

<li>Let <var>parentInternals</var> be <var>parent</var>'s <a for=EventTarget>attached internals</a>.

<li>Set <var>parent</var> to <var>parentInternals</var>'s <a
for=EventTargetInternals>eventTarget</a>.

</ol>

<li>Set <var>this</var>'s <a for=EventTargetInternals>eventTarget</a> <a>get the parent</a>
algorithm to return <var>theParent</var>.

<li>Set <var>this</var>'s {{EventTargetInternals/parent}} to <var>theParent</var>.
</ol>

<p>An <dfn export id=concept-event-listener>event listener</dfn> can be used to observe a specific
<a>event</a> and consists of:

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