[web-animations-2] Update OptionalEffectTiming.duration to accept CSSNumericValue

[saschanaz]

https://drafts.csswg.org/web-animations-2/#the-effecttiming-dictionaries

Web Animations Level 2 updates EffectTiming.duration with CSSNumericValue but not OptionalEffectTiming.duration. Maybe it should?

[birtles]

I think there's a note calling that out:

NOTE: In this version of the spec, duration is not settable as a CSSNumericValue; however, duration may be returned as a CSSNumericValue when resolving the duration in getComputedTiming(). Future versions of the spec may enable setting the duration as a CSSNumeric value, where the unit is a valid time unit or percent.

(I don't think I wrote it so I don't recall the background but just to say that this appears to be intentional.)

[saschanaz]

Ah yes, OptionalEffectTiming is only for setting values I guess.

[romainmenke]

I initially reported this with TypeScript because I thought it was an issue there, not a spec issue.

For context, our use case is reading the current timing and adjusting that.
For this purpose it is important that these values can "round trip".

function reduceDuration( timing: EffectTiming ): OptionalEffectTiming {
	if ( 'auto' === timing.duration ) {
		timing.duration = 1;
	} else {
		timing.duration = timing.duration / 1000;
	}

	return timing;
}


keyframeEffect.updateTiming(
	reduceDuration(keyframeEffect.getTiming())
);

This has been used in production for years.

With the updated typings we get TS errors, but I now also fear that the implementations might change so that the actual code might also break in the future.