In-state guards

You can check if the machine is in a certain state using an in property on a transition. The in property takes a state ID as an argument and returns true if that state node is active in the current state, which can be useful in parallel states.

In the example below, when the machine receives the LOG_WHEN_ACTIVE event, we check if the machine is in the active state, specified by id, then logIsActive.

import { createMachine } from 'xstate';

const lightMachine = createMachine(
  {
    type: 'parallel',
    states: {
      toggle: {
        initial: 'inactive',
        states: {
          inactive: {
            on: {
              TOGGLE: 'active',
            },
          },
          active: {
            id: 'active',
            on: {
              TOGGLE: 'inactive',
            },
          },
        },
      },
      logger: {
        on: {
          LOG_WHEN_ACTIVE: {
            in: '#active',
            actions: 'logIsActive',
          },
        },
      },
    },
  },
  {
    actions: {
      logIsActive: () => {
        console.log('Active!');
      },
    },
  }
);

Combining cond and in

You can combine a cond with an in property. Both the cond and the in will need to resolve to true for the machine to transition.