Generated by XState Viz: https://xstate.js.org/viz

machine.js

const nestedStates = {
  initial: 'a1',
  states: {
    a1: {
      on: {
        FOO: "a2"
      }
    },
    a2: {
      type: "final"
    }
  }
};

const machine = Machine({
  initial: 'a',
  states: {
    a: {
      onDone: "b",
      ...nestedStates
    },
    b: {}
  }
});