create.js

function createMachineEpic(machine, _, updateStoreActionFn) {
  return function epic(action$) {
    const service = interpret(machine);

    const state$ = fromEventPattern(
      handler => {
        service.onTransition(handler).start();

        return service;
      },
      (_, service) => service.stop()
    ).pipe(map(([state, action]) => updateStoreActionFn(state, action)));

    return merge(
      state$,
      action$.pipe(
        filter(({ type }) => machine.handles(type)),
        tap(action => {
          service.send(action);
        }),
        ignoreElements()
      )
    );
  };
}