[web-animations-2] Should AnimationTrigger properties be readonly?

[DavMila]

The AnimationTrigger interface is specified in the web-animations-2 spec. JavaScript can get and set the trigger property of an animation. This means that multiple animations can be associated with the same trigger. Should AnimationTrigger properties then be readonly?

If they are not readonly, then we need to specify how setting the properties of an AnimationTrigger works when multiple animations are associated with that trigger.

Specifically:

1. If an author writes:

trigger = animation.trigger;
trigger.type = new_type;

should the change affect all the animations associated with this trigger or none (do a copy-on-write for all animations associated with this trigger), orphaning the trigger?

2. If an author writes animation.trigger.type = new_type, should this affect all the other animations associated with this trigger or just the one referenced in the expression (do a copy-on-write for all other animations associated with this trigger)?

(By copy-on-write, I mean make a copy (or copies) of the old trigger and associate it (or them) with the other animations, leaving them unaffected.)

I propose we make AnimationTrigger’s properties readonly. We can relax this constraint and answer the above questions in the future if the need arises.

[ydaniv]

I propose we make AnimationTrigger’s properties readonly. We can relax this constraint and answer the above questions in the future if the need arises.

If this won't be blocked later by compat concerns and it will simplify implementation then I'm fine with the proposal + deferring.

[ydaniv]

Proposal: make properties of AnimationTrigger read-only.