gatsby-plugin-react-redux

import { createStore } from 'redux';

function reducer() {
  //...
}

// preloadedState will be passed in by the plugin
export default preloadedState => {
  return createStore(reducer, preloadedState);
};

module.exports = {
  plugins: [
    {
      resolve: `gatsby-plugin-react-redux`,
      options: {
        // [required] - path to your createStore module
        pathToCreateStoreModule: './src/state/createStore',
        // [optional] - options passed to `serialize-javascript`
        // info: https://github.com/yahoo/serialize-javascript#options
        // will be merged with these defaults:
        serialize: {
          space: 0,
          // if `isJSON` is set to `false`, `eval` is used to deserialize redux state,
          // otherwise `JSON.parse` is used
          isJSON: true,
          unsafe: false,
          ignoreFunction: true,
        },
        // [optional] - if true will clean up after itself on the client, default:
        cleanupOnClient: true,
        // [optional] - name of key on `window` where serialized state will be stored, default:
        windowKey: '__PRELOADED_STATE__',
      },
    },
  ],
};