Invoke machine in another machine but also standalone, with resetting

[sederaa]

Hi

I have a machine A that is invoked by machine B, and I need to mark the final state in A to trigger the onDone in machine B.

However, if I also want to use machine A standalone elsewhere, once it reaches the final state I can't re-run the machine (e.g. by calling a reset event) because it has reached the final state.

I want to avoid duplicating the machine A for these two usage cases (because IRL machine A is large and would otherwise be identical), so is there a way to use a machine as both an invoked machine and standalone please?

See example: https://codesandbox.io/s/suspicious-meadow-yb2du

Thanks!

[f-elix]

Hi,

I think there are a few solutions to this, depending on your precise use case. I can think of 2 right now:

1. You don't use machine A as a standalone machine, instead you can invoke it on machine B and forward the events from B (parent) to A (child). This will allow you to communicate a 'DONE' event from machine A with the sendParent() action (https://xstate.js.org/docs/guides/communication.html#invoking-machines) when entering state2, instead of having the state be final. You can then send a 'Reset' event to machine B, which will forward it to machine A.

2. You reverse the roles and instead invoke machine B from machine A, and communicate your result to machine B by using the send() action. This might be a bit too different from what you need though, I'm not sure.

[sederaa]

Hi @f-elix, thanks for your suggestions.

Since I found no good solution I now only invoke machine A from another machine, and never use it standalone. This has only required a few 'wrapper' machines so not too bad a work around.

Suggestion 1 is an interesting workaround, and I might try that instead of writing a wrapper machine next time.

Suggestion 2 doesn't suit my situation but good to bear in mind for other situations.