Yieldmachine + React

traffic-lights.jsx

import { start, on } from "https://unpkg.com/yieldmachine@0.5.1/dist/yieldmachine.module.js"

function TrafficLightsMachine() {
  const { Green, Yellow, Red } = {
    *Green() {
      yield on("timer", Yellow);
    },
    *Yellow() {
      yield on("timer", Red);
    },
    *Red() {
      yield on("timer", Green);
    }
  };
  return Red;
}

function useMachine(machineDefinition) {
  const instance = useMemo(() => {
    const aborter = new AbortController();
    const machine = start(machineDefinition, { signal: aborter.signal });
    return {
      aborter, machine, dispatch: machine.next.bind(machine)
    };
  }, []);
  useEffect(() => {
    return () => {
      instance.aborter.abort();
    };
  });

  const state = useSyncExternalStore(
    (callback) => {
      instance.machine.eventTarget.addEventListener(
        "StateChanged",
        callback
      );
      return () => {
        instance.machine.eventTarget.removeEventListener(
          "StateChanged",
          callback
        );
      };
    },
    () => instance.machine.value,
    () => instance.machine.value
  );

  return Object.freeze([state, instance.dispatch]);
}

export default function App() {
  const [value, dispatch] = useMachine(TrafficLightsMachine);

  return <article class="flex flex-col gap-2 items-center text-lg">
  <dl>
    <div className="flex gap-2">
      <dt className="font-bold">State:</dt>
      <dd>{value.state}</dd>
    </div>
    <div className="flex gap-2">
      <dt className="font-bold">Change</dt>
      <dd>{"#"}{value.change}</dd>
    </div>
  </dl>
    <button className="px-3 py-1 text-white bg-black rounded-lg" onClick={() => dispatch("timer")}>send event: timer</button>
  </article>;
}