mobx-example.ts

class Controller {
  @mobx.observable.ref count = 0;

  @action
  increment() {
    this.count += 1;
  }
}

// exposing a controller for a singleton component
function createCount() {
  const countCtrl = new Controller();
  const Count = observer(() => (
    <div>Count {countCtrl.count}</div>
  ));
  return { Count, countCtrl };
}

const { countCtrl, Count } = createCount();
const appRoot = document.getElementById("root");

ReactDOM.render(appRoot, <Count/>);
setTimeout(() => count.increment(), 1000);