Transition of "type: decay" appears to be broken

[xzilja]

Is there an existing issue for this?

• [X] I have searched the existing issues

Do you want this issue prioritized?

• [ ] Yes, I have sponsored
• [X] Not urgent

Current Behavior

React native reanimated library exposes withDecay helper documented here https://docs.swmansion.com/react-native-reanimated/docs/animations/withDecay it appears from the source that moti also supports this by setting transition to type: 'decay' however, doing so breaks the app. with following error:

Unhandled Runtime Error
TypeError: animation.callback is not a function

Expected Behavior

Should not break and allow to use decay animations.

Steps To Reproduce

1. Visit hello world example at https://moti.fyi/hello-world
2. Change transition type from timing to decay in the example and save
3. Test with other values like timing and spring, seems to work ok

Versions

- Moti: 0.27.0
- Reanimated: 3.5.4
- React Native: 0.72.6

Screenshots

https://github.com/nandorojo/moti/assets/3154053/8ec72422-fe31-4fea-88d3-04df5114d13c

Reproduction

https://stackblitz.com/edit/nextjs-9sshqj?file=pages%2Findex.tsx

[xzilja]

Related discussions that can be closed if this is an actual bug in favor of this issue.

https://github.com/nandorojo/moti/discussions/319 https://github.com/nandorojo/moti/discussions/313

[nandorojo]

Is it web only? Can you confirm it works with normal reanimated but just not moti?

[xzilja]

Bug initially popped up for me on ios, validated it with web playground. I'll whip up a test with vanilla reanimated in a moment to confirm 👍

[nandorojo]

Cool thanks

[xzilja]

Alright, reproduction for this actually needs to be hooked to gesture (that's how withDecay) works essentially. With reanimated, this behaves as expected

const pan = Gesture.Pan()
    .onChange(({ translationY }) => {
        translate.value = translationY;
    })
    .onFinalize(({ velocityY }) => {
        translate.value = withDecay({
           velocity: velocityY
        });
    })

But this (what I believe is equivalent with moti) throws an error when it hits animation with decay

const pan = Gesture.Pan()
    .onChange(({ translationY }) => {
      animationState.animateTo({ translateY: translationY, transition: { type: 'no-animation' } })
    })
    .onFinalize(({ velocityY }) => {
      animationState.animateTo({ translateY: 0, transition: { type: 'decay', velocity: velocityY } })
    })

I might be missing out on some differences between decay and say spring animation api's within moti, in this case, perhaps an example with decay in the docs could be good?

[nandorojo]

How does reanimated perform if you add these values:

      velocity: 2,
      deceleration: 2,

[xzilja]

It seems to bug out / shoot everything off to the distance 😅

I copied and set up example from reanimated in this expo snack https://snack.expo.dev/@asimetriq/juicy-indigo-raspberries?

Set values back to normal, but you can set velocity and decay to 2 on line ~30 to see the effect

[nandorojo]

Can you try moti@0.26.1?

[nandorojo]

I'm wondering if withDecay is broken on Web altogether from reanimated

[xzilja]

Getting same error on 0.26.1 as well (testing on ios with fresh node_modules install and ios project rebuild)

[nandorojo]

How odd, and it works with plain reanimated?

[xzilja]

Yes, working example is in the snack I provided above by copying from reanimated's docs. (also tested locally on my own implementation).