Redux

// src/index.js

// Grab the state from a global variable injected into the server-generated HTML
const preloadedState = window.__PRELOADED_STATE__

// Allow the passed state to be garbage-collected
delete window.__PRELOADED_STATE__

const store = createStore(
  reducer,
  preloadedState,
  applyMiddleware(thunk)
)

// server/app.js

import path from "path";
import React from "react";
import { Provider } from "react-redux";
import { createReactAppExpress } from "@cra-express/core";

import App from "../src/App";
import configureStore from "../src/store/index.js";
const clientBuildPath = path.resolve(__dirname, "../client");

function handleUniversalRender(req, res) {
  const initialState = {};
  const store = configureStore(initialState);
  const appEl = (
    <Provider store={store}>
      <App />
    </Provider>
  );
  return appEl;
}

const app = createReactAppExpress({
  clientBuildPath,
  universalRender: handleUniversalRender,
  onFinish(req, res, html) {
    const state = store.getState();
    const finalHtml = html.replace('{{SCRIPT}}', `<script>
      window.__PRELOADED_STATE__ = ${JSON.stringify(state).replace(/</g, '\\u003c')};
    </script>`);
    res.send(finalHtml);
  }
});

export default app;

References: https://redux.js.org/recipes/server-rendering