Allow for customisation of the "get the parent" algorithm #1230
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keithamus
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Some initial feedback. Mainly around how to organize this. Overall I think this works, but would love to hear from @rniwa and @smaug---- especially.
dom.bs
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| <p>Each {{EventTarget}} object also has an associated <dfn export>get the parent</dfn> algorithm, | ||
| which takes an <a>event</a> <var>event</var>, and returns an {{EventTarget}} object. Unless | ||
| specified otherwise it returns null. | ||
| which takes an <a>event</a> <var>event</var>, and returns an {{EventTarget}}. Unless otherwise | ||
| specified otherwise it returns the associated <a for=EventTarget>attached internals</a><a | ||
| for=EventTargetInternals">parent</a> attribute. |
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I think instead we should make the parent setter overwrite this algorithm with an algorithm that returns the given value.
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Okay I've added some steps which I think resolve this but let me know, I'm sure it could use some refinement.
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| for=EventTargetInternals>eventTarget</a> then<a>throw</a> a "{{HierarchyRequestError!!exception}}" | ||
| {{DOMException}}. | ||
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| <li>Set <var>internal</var>'s <a for=EventTargetInternals>eventTarget</a> <a>get the parent</a> |
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I couldn't find precedent for setting an algorithm so this is just made up, hopefully it suffices?
keithamus
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| @@ -1322,6 +1373,9 @@ property of the event being dispatched. | |||
| <p>While <var>parent</var> is non-null:</p> | |||
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| <ol> | |||
| <li>If the <var>event</var>'s <a for=Event>path</a> <a for=set>contains</a> <var>parent</var> | |||
| then <a>throw</a> a "{{HierarchyRequestError!!exception}}" {{DOMException}}. | |||
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This would be slow. I don't think we can do this in normal case when dispatching events to dom tree. The relevant code in implementations is so hot that extra virtual c++ calls show up, as an example.
We need to ensure that there are now loops when setting up the parents. That is already done for DOM nodes anyhow - DOM tree doesn't contain loops.
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Would you prefer us to check the chain during setting of the parent? Would that suffice?
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Okay I think I've resolved this
| 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.
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This modifies the EventTarget IDL to allow assignment of a parent EventTarget to an EventTarget instance, while also modifying the "get the parent" algorithm to default to returning that instance. It also modifies the Event Dispatch algorithm to ensure that custom parent chains cannot cause loops.
keithamus
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This modifies the EventTarget IDL to allow assignment of a parent EventTarget to an EventTarget instance, while also modifying the "get the parent" algorithm to default to returning that instance.
It also modifies the Event Dispatch algorithm to ensure that custom parent chains cannot cause loops.
(See WHATWG Working Mode: Changes for more details.)
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