How to use SpringUtils from a worklet?

[Ashoat]

Problem

I have some Reanimated 1 code that I'm trying to convert to Reanimated 2. In the original code we use SpringUtils.makeConfigFromBouncinessAndSpeed and SpringUtils.makeDefaultConfig.

I want to use these SpringUtils methods in the new code, but it doesn't seem to be possible from within a worklet.

Things I've tried

springConfig declared at top level

const springConfig = {
  ...SpringUtils.makeConfigFromBouncinessAndSpeed({
    ...SpringUtils.makeDefaultConfig(),
    bounciness: 10,
    speed: 8,
  }),
  overshootClamping: true,
};

function makeSpringConfig(velocity: number) {
  'worklet';
  return {
    ...springConfig,
    velocity,
  };
}

This led to an error when starting the animation:

Tried to synchronously call function {assign} from a different thread.

springConfig declared in worklet

function makeSpringConfig(velocity: number) {
  'worklet';
  const springConfig = {
    ...SpringUtils.makeConfigFromBouncinessAndSpeed({
      ...SpringUtils.makeDefaultConfig(),
      bounciness: 10,
      speed: 8,
    }),
    overshootClamping: true,
  };
  return {
    ...springConfig,
    velocity,
  };
}

This led to an error when starting the animation:

Tried to synchronously call function {makeDefaultConfig} from a different thread.

Storing springConfig in a shared value

const springConfig = {
  ...SpringUtils.makeConfigFromBouncinessAndSpeed({
    ...SpringUtils.makeDefaultConfig(),
    bounciness: 10,
    speed: 8,
  }),
  overshootClamping: true,
};

[...]

const sharedSpringConfig = useSharedValue(springConfig);

[...]

onEnd: event => {
  translateX.value = withSpring(0, {
    ...sharedSpringConfig.value,
    velocity: event.velocityX,
  });
},

I thought this one would work, but I got the same issue:

Tried to synchronously call function {assign} from a different thread.

Running SpringUtils in a REPL and copy-pasting results in

I tried to search for examples of withSpring called with a SpringConfig in the repo. I only found one that was specifying a full list of config options, and it was just manually defined.

I was able to get this working by just transcribing the results from a REPL. But this feels pretty hacky.

function makeSpringConfig(velocity: number) {
  'worklet';
  return {
    stiffness: 257.1370588235294,
    damping: 19.003038357561845,
    mass: 1,
    overshootClamping: true,
    restDisplacementThreshold: 0.001,
    restSpeedThreshold: 0.001,
    velocity,
  };
}

Possible solutions

• It would be great if SpringUtils (or an alternative) was available from within worklets!
• Alternately, it would be great if there was a way to construct some shared state on the JS thread and then pass it to the UI thread. I thought useSharedValue was supposed to do this, but it didn't seem to work...