withReduxSaga.js

import React from "react";
import { END } from "redux-saga";

const STORE_KEY = "__NEXT_REDUX_STORE__";

export const withReduxSaga = makeStore => {
  const isServer = typeof window === "undefined";

  const initStore = ({ initialState, ctx }) => {
    const createStore = () =>
      makeStore(initialState, {
        ...ctx,
        isServer
      });

    if (isServer) {
      return createStore();
    }

    if (!window.hasOwnProperty(STORE_KEY)) {
      window[STORE_KEY] = createStore();
    }

    return window[STORE_KEY];
  };

  return App => {
    const WrappedApp = foo => {
      const { initialState } = foo;
      const store = initStore({ initialState });
      const { initialProps, ...props } = foo;
      return <App {...props} {...initialProps} store={store} />;
    };

    WrappedApp.getInitialProps = async props => {
      const { ctx } = props;

      const store = initStore({ ctx });

      ctx.store = store;
      ctx.isServer = isServer;

      const initialProps = App.getInitialProps
        ? await App.getInitialProps.call(App, props)
        : {};

      if (isServer) {
        store.dispatch(END);
        await store.sagaTask.toPromise();
      }

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

    return WrappedApp;
  };
};