There are a number of ways we can deal with sub-states in XState. We will start with a list of the options and then follow up with questions you can ask yourself when helping to decide which pattern to use.

The patterns

External

• This is when the parent service and child service no nothing of each other.

Hierarchy

• Sharing context
• communicate through ids

Invoked Machine service

• on done final state
• mocking in testing
• Belongs to a state

Actor machine

• update state through message events
• dynamic
• manual stop
• Belong to the service

The Questions

Do my sub-states need to keep up to date with the parent context. Are the sub-states always the same. Do I need to mock out the sub-states.