a quick implementation of redux-obesrvable middleware

redux-observable.js

import { Subject } from "rxjs";

export const createMiddleware = () => {
  const [action$, state$] = [new Subject(), new Subject()];
  const middleware = store => {
    return dispatch => {
      middleware.run = epic => epic(action$, state$).subscribe(store.dispatch);
      return action => {
        const result = dispatch(action);
        action$.next(action);
        state$.next(store.getState());
        return result;
      };
    };
  };
  return middleware;
};