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

machine.js

const createSingleState = () => ({
  initial: "fetch",
  states: {
    fetch: {
      invoke: {
        src: "fetchSmth",
        onDone: {
          target: "done",
          actions: "notifySingleSuccess"
        }
      }
    },
    done: {
      type: "final"
    }
  }
});

const testMachine = Machine(
  {
    id: "test",
    type: "parallel",
    onDone: {
      actions: "notifyBothSuccess"
    },
    states: {
      first: createSingleState(),
      second: createSingleState()
    }
  },
  {
    actions: {
      notifySingleSuccess: () => console.log(Date.now(), "single success"),
      notifyBothSuccess: () => console.log(Date.now(), "both success")
    },
    services: {
      fetchSmth: () => {
        const ms = Math.floor(Math.random() * 1000);
        console.log("gonna resolve in", ms);
        return new Promise(resolve =>
          setTimeout(() => {
            console.log(Date.now(), "resolving single");
            resolve();
          }, ms)
        );
      }
    }
  }
);