As of 12/5/2017 this is only present in Firefox Nightly and Chrome Canary 65+
The Web Animations API introduces the concept of two animations modifying the same property and evaluating their composite value. through a new effect property:
So in the case of a transform, if one animation modifies a
transform: translateX() and another modifies a
transform: scale() the API will be able to produce a result that accounts for both... even if they have different easing, duration, iterations, etc.
Notice as you add animations that the durations are all different and their start times are all different... meaning the browser is combining all the values for you.
You can also view a similar example that does not need
composite support where it nests a new DOM element for each animation.