AnimationEffect.getComputedTiming() - Web APIs
return value a computedeffecttiming dictionary object, which contains the following properties: endtime the end time of the animation in milliseconds from the animation's start (if the keyframeeffect is associated with an animation).

Using the Web Animations API - Web APIs
t, do so by referencing alicechange’s animation.effect property, which returns an object containing all the details of the effect(s) active on alice: alicechange.currenttime = alicechange.effect.getcomputedtiming().duration / 2; effect lets us access the animation’s keyframes and timing properties — alicechange.effect.getcomputedtiming() points to alice’s timing object (which is of type computedeffecttiming) — this contains her computedeffecttiming.duration.