gatsby-browser.js

import React from "react";
import { Provider } from "react-redux";
import { Router } from "react-router-dom";
import createStore from "./src/state";

exports.replaceRouterComponent = ({ history }) => {
  const store = createStore();
  const ConnectedRouterWrapper = ({ children }) => (
    <Provider store={store}>
      <Router history={history}>{children}</Router>
    </Provider>
  );

  return ConnectedRouterWrapper;
};