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Snapshot Model

machine.getSnapshot() returns the full observable runtime state.

Shape​

type JourneySnapshot<TContext, TStepId extends string> = {
  current: TStepId;
  context: TContext;
  history: readonly TStepId[];
  visited: readonly TStepId[];
  status: "running" | "complete" | "closed";
  async: {
    isLoading: boolean;
    byStep: Record<
      TStepId,
      {
        phase: "idle" | "evaluating-when" | "running-effect" | "error";
        eventType: string | null;
        transitionId: string | null;
        error: unknown | null;
      }
    >;
  };
};

Field Semantics​

  • current: active step.
  • context: current business state.
  • history: stack-like trail of previous steps.
  • visited: unique ordered trail of all reached steps.
  • status: running or terminal (complete/closed).

Invariants​

  • visited always contains current.
  • history can be trimmed independently of visited.
  • async.byStep exists for every declared step.

Subscription Pattern​

const unsubscribe = machine.subscribe(() => {
  const snapshot = machine.getSnapshot();
  console.log(snapshot.current, snapshot.status);
});

unsubscribe();

UI Derivations​

Example derived booleans (with known step IDs in your app):

  • isReviewStep = snapshot.current === reviewStepId
  • isTerminal = snapshot.status !== "running"
  • stepLoading = snapshot.async.byStep[snapshot.current].phase !== "idle"

Keep derivation in render logic or selectors instead of storing duplicated state.