redux practical application

import { createStore, applyMiddleware, compose } from 'redux';
import thunkMiddleware from 'redux-thunk';
import rootReducer from 'reducers/index';
import DevTools from 'containers/DevTools'

export default function configureStore(preloadedState) {
  const store = createStore(
    rootReducer,
    preloadedState,
    compose(
      applyMiddleware(thunkMiddleware),
      DevTools.instrument()
    )
  )

  if (module.hot) {
    // Enable Webpack hot module replacement for reducers
    module.hot.accept('../reducers', () => {
      const nextRootReducer = require('../reducers').default
      store.replaceReducer(nextRootReducer)
    })
  }

  return store
}

function applyMiddleware() {
  for (var _len = arguments.length, middlewares = Array(_len), _key = 0; _key < _len; _key++) {
    middlewares[_key] = arguments[_key];
  }

  return function (createStore) {
    return function (reducer, preloadedState, enhancer) {
      var store = createStore(reducer, preloadedState, enhancer);
      var _dispatch = store.dispatch;
      var chain = [];

      var middlewareAPI = {
        getState: store.getState,
        dispatch: function dispatch(action) {
          return _dispatch(action);
        }
      };
      chain = middlewares.map(function (middleware) {
        return middleware(middlewareAPI);
      });
      _dispatch = compose.apply(undefined, chain)(store.dispatch);

      return _extends({}, store, {
        dispatch: _dispatch
      });
    };
  };
}

function compose() {
  for (var _len = arguments.length, funcs = Array(_len), _key = 0; _key < _len; _key++) {
    funcs[_key] = arguments[_key];
  }

  if (funcs.length === 0) {
    return function (arg) {
      return arg;
    };
  }

  if (funcs.length === 1) {
    return funcs[0];
  }

  return funcs.reduce(function (a, b) {
    return function () {
      return a(b.apply(undefined, arguments));
    };
  });
}

function createThunkMiddleware(extraArgument) {
  return function (_ref) {
      var dispatch = _ref.dispatch,
          getState = _ref.getState;
      return function (next) {
          return function (action) {
              if (typeof action === 'function') {
                  return action(dispatch, getState, extraArgument);
              }

              return next(action);
          };
      };
  };
}

var thunk = createThunkMiddleware();


function createStore(reducer, preloadedState, enhancer) {
  var _ref2;

  if (typeof preloadedState === 'function' && typeof enhancer === 'undefined') {
    enhancer = preloadedState;
    preloadedState = undefined;
  }

  if (typeof enhancer !== 'undefined') {
    if (typeof enhancer !== 'function') {
      throw new Error('Expected the enhancer to be a function.');
    }

    return enhancer(createStore)(reducer, preloadedState);
  }

  if (typeof reducer !== 'function') {
    throw new Error('Expected the reducer to be a function.');
  }

  var currentReducer = reducer;
  var currentState = preloadedState;
  var currentListeners = [];
  var nextListeners = currentListeners;
  var isDispatching = false;

  function ensureCanMutateNextListeners() {
    if (nextListeners === currentListeners) {
      nextListeners = currentListeners.slice();
    }
  }

  function getState() {
    return currentState;
  }

  function subscribe(listener) {
    if (typeof listener !== 'function') {
      throw new Error('Expected listener to be a function.');
    }
    var isSubscribed = true;
    ensureCanMutateNextListeners();
    nextListeners.push(listener);

    return function unsubscribe() {
      if (!isSubscribed) {
        return;
      }
      isSubscribed = false;
      ensureCanMutateNextListeners();
      var index = nextListeners.indexOf(listener);
      nextListeners.splice(index, 1);
    };
  }

  function dispatch(action) {
    if (!isPlainObject(action)) {
      throw new Error('Actions must be plain objects. ' + 'Use custom middleware for async actions.');
    }
    if (typeof action.type === 'undefined') {
      throw new Error('Actions may not have an undefined "type" property. ' + 'Have you misspelled a constant?');
    }
    if (isDispatching) {
      throw new Error('Reducers may not dispatch actions.');
    }
    try {
      isDispatching = true;
      currentState = currentReducer(currentState, action);
    } finally {
      isDispatching = false;
    }
    var listeners = currentListeners = nextListeners;
    for (var i = 0; i < listeners.length; i++) {
      var listener = listeners[i];
      listener();
    }
    return action;
  }

  function replaceReducer(nextReducer) {
    if (typeof nextReducer !== 'function') {
      throw new Error('Expected the nextReducer to be a function.');
    }
    currentReducer = nextReducer;
    dispatch({ type: ActionTypes.INIT });
  }

  function observable() {
    var _ref;
    var outerSubscribe = subscribe;
    return _ref = {
      subscribe: function subscribe(observer) {
        if (typeof observer !== 'object') {
          throw new TypeError('Expected the observer to be an object.');
        }
        function observeState() {
          if (observer.next) {
            observer.next(getState());
          }
        }
        observeState();
        var unsubscribe = outerSubscribe(observeState);
        return { unsubscribe: unsubscribe };
      }
    }, _ref[result] = function () {
      return this;
    }, _ref;
  }
  dispatch({ type: ActionTypes.INIT });
  return _ref2 = {
    dispatch: dispatch,
    subscribe: subscribe,
    getState: getState,
    replaceReducer: replaceReducer
  }, _ref2[result] = observable, _ref2;
}