xstate v5: a "before stop" action?

[boneskull]

I have two machines, A and B. A is the "root" machine. B is stateless and only sends & receives events.

A spawns B in response to an event. In response to a later event, A stops B via stopChild().

Is it possible to configure B such that it executes a final action just before it is stopped--e.g., log that it is stopping?

Would I need to add states to B to make something like this work? For example, send an event from A to B which causes B to enter a final state, then call stopChild() after?

I've tried adding an exit action to B's config, but it does not execute; I don't understand what an exit action is supposed to do if it is not associated with a particular state.

[davidkpiano]

I suppose an onStop: { … } transition could be helpful here (cc. @Andarist)

[boneskull]

Thanks. Regarding my last question above,

I don't understand what an exit action is supposed to do if it is not associated with a particular state.

Given a machine without any state, I'm still unclear why this is the way it is:

const machine = createMachine({
  entry: 'hello',
  exit: 'goodbye',
  // anything else
})

It appears that when the machine is created, the hello action will be executed. But the goodbye action will never be executed, right? Is there any case in which the exit action makes sense at the top-level? If not, why couldn't exit be used as onStop?

[davidkpiano]

A top-level exit action is called when the machine reaches a top-level final state; i.e. when the machine completes.