sendState.js

const { Provider } = ReactRedux;

window.addEventListener("message", e => {
  // extentions and other 3rd party scripts talk via postMeessage api(same orgin)
  // so it is very important to filter those events
  if (e.origin !== window.location.origin || !e.data || e.data.source !== "dialog-message") {
    return;
  }

  // parent and window are same thing if the current page is not in any frame
  if (window !== parent) {
    parent.postMessage(
      { messageRecieved: true, source: "dialog-message" },
      `${window.location.origin}/iframe-testing-ground`
    );
  }

  const state = Object.assign({}, e.data);
  window.redux_store.dispatch(window.redux_actions.loadInitialState(state));
});

window.sendState = () => {
  window.postMessage(window.redux_store.getState(), `${window.location.origin}`);
};

ReactDOM.render(
  <Provider store={window.redux_store}>
    <PrintDialog />
  </Provider>,
  document.getElementById("root")
);