next.js/examples/with-redux/utils/withRedux.js

import React from 'react'
import { connect, Provider } from 'react-redux'

const __NEXT_REDUX_STORE__ = '__NEXT_REDUX_STORE__'

// https://github.com/iliakan/detect-node
const checkServer = () => Object.prototype.toString.call(global.process) === '[object process]'

const getOrCreateStore = (initStore, initialState) => {
  // Always make a new store if server
  if (checkServer() || typeof window === 'undefined') {
    return initStore(initialState)
  }

  // Store in global variable if client
  if (!window[__NEXT_REDUX_STORE__]) {
    window[__NEXT_REDUX_STORE__] = initStore(initialState)
  }
  return window[__NEXT_REDUX_STORE__]
}

export default (...args) => (Component) => {
  // First argument is initStore, the rest are redux connect arguments and get passed
  const [initStore, ...connectArgs] = args

  const ComponentWithRedux = (props = {}) => {
    const { store, initialProps, initialState } = props

    // Connect page to redux with connect arguments
    const ConnectedComponent = connect.apply(null, connectArgs)(Component)

    // Wrap with redux Provider with store
    // Create connected page with initialProps
    return React.createElement(
      Provider,
      { store: store && store.dispatch ? store : getOrCreateStore(initStore, initialState) },
      React.createElement(ConnectedComponent, initialProps)
    )
  }

  ComponentWithRedux.getInitialProps = async (props = {}) => {
    const isServer = checkServer()
    const store = getOrCreateStore(initStore)

    // Run page getInitialProps with store and isServer
    const initialProps = Component.getInitialProps
      ? await Component.getInitialProps({ ...props, isServer, store })
      : {}

    return {
      store,
      initialState: store.getState(),
      initialProps
    }
  }

  return ComponentWithRedux
}