xstate.assign event

[gkiely]

A lot of the time when I assign a new value in an invoked actor, I would like to reflect some portion of that in the parent.

When using sync: true, xstate.update fires for every change to an invoked actor. It would be nice if there was an xstate.assign or xstate.context event and xstate.state to distinguish between a change to context and state.

Alternatively, something like assignAndSendToParent would also be helpful.

[davidkpiano]

Interesting idea; with observables as an analogy, you basically want to map/filter over the "emitted" values of the actor, and listen for those specific values, right?

One nice addition that is coming to v5 is onSnapshot, which is like onDone and onError but for emitted (snapshot) values from actors:

// TENTATIVE v5 API
invoke: {
  src: someMachine,
  onSnapshot: {
    actions: (ctx, { data }) => {
      // `data` is the snapshot value
    }
  }
}

So that would be the first step to doing what you want; you can add a guard to help constrain but it looks like you want something more like a "selector".

Alright, this gives me some good food for thought.

[gkiely]

I think this would let me achieve what I’m trying to do.