Add cancelable operator

[igorkamyshev]

Some effects should be cancelled because of different events. So, I propose to add operator cancellable, for creation cancellable effect.

Reference:

• https://github.com/doasync/fry-fx — it handles cancellable effects, but depends on AbortController and requires a lot of boring work.

API proposition:

const internalFx = createEffect(({ onCancel, ...otherParams }) => {
  // ...
  onCancel(() => {
    // ...
  })
})

const cancel = createEvent()

// Cancelled by event
const fx1 = cancellable({ effect: internalFx, trigger: cancel })

const turnOff = createEvent()
const $enabled = createStore(true)
  .on(turnOff, () => false)

// Cancelled by store value changed to `false`
const fx1 = cancellable({ effect: internalFx, grant: $enabled })

With this API, we can reimplement the most parts of fry-fx and effector-reeffect.

What do you think of this proposal? If you are OK with it, I try to implement naive version of it in PR.

[sergeysova]

Maybe it is better to name it in style of effector fabric-methods: createCancellable

[igorkamyshev]

But it isn't fabric. My proposal have a form of an operator.

[zerobias]

attach doesn’t have create- suffix, so this is not a requirement. ability to pass units to parameters is more important

[yumauri]

Raw try to implement base cancellable (supports cancel only by event):
https://share.effector.dev/hC05veNs
It could be extended, but I’m not sure about fork support with this approach...

[AlexandrHoroshih]

It doesn't work with fork 🤔
My guess it is due to usage of Promice.race with both effect and non-effect async functions as params - this way effector loses tracks of original effect - and allSettled just never ends
https://share.effector.dev/Eef9ugIC

I did a very similiar (but a little sloppy) implementation for this case a couple months ago, which can work in forked scope
It is more like a fabric for cancellable effects, but can work with effects too

UPD: apparently, using an effect as a handler in this implementation leads to the same problem - allSettled never ends 🤔
Usual function works correctly.
Actually, it is just not properly used onCancel callback 🤔 - it should also reject that Promise, so whole thing works correctly, it is user-side bug. Working example (promise rejected too): https://share.effector.dev/xnqn2l85

[yumauri]

Damn fork, it never works 😅
Issue here is with cleanup function, which just cancels timeout and original effect just never ends. Whereas needFxCounter field is decremented on finally event, which is never launched.
Little fast workaround for that, I can think of — use actual handler instead of effect in Promise.race → https://share.effector.dev/KHZnL26w
But this will not work with attached effects, I guess...

[yumauri]

One more issue with my code — single instance of cleanup function for cancellable effects. And in result, cleanup actually works just for latest effect call :(

[zerobias]

request cancellation for effector 22 and fork api

[AlexandrHoroshih]

Possible implementation here, feel free to join discussion
#168