rigging-multi-root.js

const store = createStore(/* ... */);

// ...

ReactDOM.render(
  <Provider store={store}>
    <MyCompA />
  </Provider>,
  document.getElementById('mountsite-A')
);

ReactDOM.render(
  <Provider store={store}>
    <MyCompB />
  </Provider>,
  document.getElementById('mountsite-B')
);