Mutator: (() => void)

A function that is supposed to mutate the properties of JavaScript objects by utilizing the result of calling AnimClip.computeTween (or by utilizing the result of some other value that may already be updating onscreen). The function will automatically run on every frame (as in, the device's frame rate), and the output of AnimClip.computeTween automatically changes on every frame according to the clip's duration, so the outcome is ultimately the illusion of a smooth animation because the target JavaScript properties will change at the device's frame rate.

Used in ComposedEffect.

The reason the return type is void is because there is no need to return any value since the mutation should occur directly within the function.