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Journey

Machine surface

buildMachineSurface (src/core/machine.ts) creates the public machine object once. Its grouped methods close over a runtime; they do not hold independent copies of journey state.

machine
  getSnapshot()
  controls.*          start, pause, resume, complete, terminate, restart
  navigate.*          goToStepById, goToNextStep, goToPreviousStep,
                      goToLastVisitedStep
  subscriptions.*     subscribe, subscribeEvent
  context.update()
  async.clearError()
  plugins.*           one namespaced entry per plugin
  dispose()
  send()              graph only

The object (and every nested group) is referentially stable for the machine’s lifetime, so it can be captured once, passed through props or context, and used in effect dependencies without re-subscribing. Everything that changes is read from the immutable snapshot.

Group responsibilities

Section titled “Group responsibilities”
  • controls — synchronous lifecycle verbs. Each returns a boolean indicating whether the status change applied.
  • navigate — Promise-based movement, resolving to an ok-discriminated NavigationResult. Linear machines additionally expose goToStepByIndex(index).
  • send(event) — graph machines only, at the top level. Its presence is the machine-type discriminant: linear machines have no event system.
  • subscriptions — synchronous subscribe calls returning unsubscribe functions, delegated to the store.
  • context.update — synchronous context replacement.
  • async.clearError — clears the current step’s work or hook error.
  • plugins — the namespaced API record contributed by plugin setup() calls.

Where to next

Section titled “Where to next”