Redux without the sanity checks in a single file. Don't use this, use normal Redux. :-) . Simplify for beginner

slim-redux.js

import { mapValues, pick, compose } from 'lodash';

function bindActionCreator(actionCreator, dispatch) {
  return (...args) => dispatch(actionCreator(...args));
}

export function bindActionCreators(actionCreators, dispatch) {
  return typeof actionCreators === 'function' ?
    bindActionCreator(actionCreators, dispatch) :
    mapValues(actionCreators, actionCreator =>
      bindActionCreator(actionCreator, dispatch)
    );
}

/* applyMiddleware is totally optional. You can ignore this at the beginning. */
// export function applyMiddleware(...middlewares) {
//   return (next) => (reducer, initialState) => {
//     var store = next(reducer, initialState);
//     var dispatch = store.dispatch;
//     var chain = [];

//     chain = middlewares.map(middleware => middleware({
//       getState: store.getState,
//       dispatch: (action) => dispatch(action)
//     }));
//     dispatch = compose(...chain)(store.dispatch);

//     return { ...store, dispatch };
//   };
// }

export function combineReducers(reducers) {
  var finalReducers = pick(reducers, (val) => typeof val === 'function');
  return (state = {}, action) => mapValues(finalReducers,
    (reducer, key) => reducer(state[key], action)
  );
}

export function createStore(reducer, initialState) {
  var currentReducer = reducer;
  var currentState = initialState;
  var listeners = [];
  var isDispatching = false;

  function getState() {
    return currentState;
  }

  function subscribe(listener) {
    listeners.push(listener);

    return function unsubscribe() {
      var index = listeners.indexOf(listener);
      listeners.splice(index, 1);
    };
  }

  function dispatch(action) {
    if (isDispatching) {
      throw new Error('Reducers may not dispatch actions.');
    }

    try {
      isDispatching = true;
      currentState = currentReducer(currentState, action);
    } finally {
      isDispatching = false;
    }

    listeners.slice().forEach(listener => listener());
    return action;
  }

  function replaceReducer(nextReducer) {
    currentReducer = nextReducer;
    dispatch({ type: '@@redux/INIT' });
  }

  dispatch({ type: '@@redux/INIT' });

  return { dispatch, subscribe, getState, replaceReducer };
}