Copy of Redux' createStore to ease migrations from Flux to Redux

createFluxStore.js

// This file is base is based on https://github.com/vivek3003/flux-redux-migration, with some modifications
// for flux's actionTypes and other validations

import isPlainObject from 'lodash/isPlainObject';
import { createStore } from 'redux';
/**
 * This is a copy of Redux's createStore. Only the dispatch function is modified.
 * It passes the action Type as parameter to the callbacks registered by store.subscribe *
 * /


/**
 * These are private action types reserved by Redux.
 * For any unknown actions, you must return the current state.
 * If the current state is undefined, you must return the initial state.
 * Do not reference these action types directly in your code.
 */
export var ActionTypes = {
    INIT: '@@redux/INIT'
};

/**
 * Creates a Redux store that holds the state tree.
 * The only way to change the data in the store is to call `dispatch()` on it.
 *
 * There should only be a single store in your app. To specify how different
 * parts of the state tree respond to actions, you may combine several reducers
 * into a single reducer function by using `combineReducers`.
 *
 * @param {Function} reducer A function that returns the next state tree, given
 * the current state tree and the action to handle.
 *
 * @param {any} [initialState] The initial state. You may optionally specify it
 * to hydrate the state from the server in universal apps, or to restore a
 * previously serialized user session.
 * If you use `combineReducers` to produce the root reducer function, this must be
 * an object with the same shape as `combineReducers` keys.
 *
 * @param {Function} enhancer The store enhancer. You may optionally specify it
 * to enhance the store with third-party capabilities such as middleware,
 * time travel, persistence, etc. The only store enhancer that ships with Redux
 * is `applyMiddleware()`.
 *
 * @returns {Store} A Redux store that lets you read the state, dispatch actions
 * and subscribe to changes.
 */
export default function createFluxStore(reducer, initialState, enhancer) {
    if (typeof initialState === 'function' && typeof enhancer === 'undefined') {
        enhancer = initialState;
        initialState = undefined;
    }

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

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

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

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

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

    /**
     * Reads the state tree managed by the store.
     *
     * @returns {any} The current state tree of your application.
     */
    function getState() {
        return currentState;
    }

    /**
     * Adds a change listener. It will be called any time an action is dispatched,
     * and some part of the state tree may potentially have changed. You may then
     * call `getState()` to read the current state tree inside the callback.
     *
     * You may call `dispatch()` from a change listener, with the following
     * caveats:
     *
     * 1. The subscriptions are snapshotted just before every `dispatch()` call.
     * If you subscribe or unsubscribe while the listeners are being invoked, this
     * will not have any effect on the `dispatch()` that is currently in progress.
     * However, the next `dispatch()` call, whether nested or not, will use a more
     * recent snapshot of the subscription list.
     *
     * 2. The listener should not expect to see all states changes, as the state
     * might have been updated multiple times during a nested `dispatch()` before
     * the listener is called. It is, however, guaranteed that all subscribers
     * registered before the `dispatch()` started will be called with the latest
     * state by the time it exits.
     *
     * @param {Function} listener A callback to be invoked on every dispatch.
     * @returns {Function} A function to remove this change listener.
     */
    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);
        };
    }

    /**
     * Dispatches an action. It is the only way to trigger a state change.
     *
     * The `reducer` function, used to create the store, will be called with the
     * current state tree and the given `action`. Its return value will
     * be considered the **next** state of the tree, and the change listeners
     * will be notified.
     *
     * The base implementation only supports plain object actions. If you want to
     * dispatch a Promise, an Observable, a thunk, or something else, you need to
     * wrap your store creating function into the corresponding middleware. For
     * example, see the documentation for the `redux-thunk` package. Even the
     * middleware will eventually dispatch plain object actions using this method.
     *
     * @param {Object} action A plain object representing “what changed”. It is
     * a good idea to keep actions serializable so you can record and replay user
     * sessions, or use the time travelling `redux-devtools`. An action must have
     * a `type` property which may not be `undefined`. It is a good idea to use
     * string constants for action types.
     *
     * @returns {Object} For convenience, the same action object you dispatched.
     *
     * Note that, if you use a custom middleware, it may wrap `dispatch()` to
     * return something else (for example, a Promise you can await).
     */
    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') {
            if (typeof action.actionType === 'undefined') {
                throw new Error(
                    'Actions may not have an undefined "type" property. ' +
                        'Have you misspelled a constant?'
                );
            } else {
                action.type = action.actionType;
            }
        }

        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++) {
            listeners[i](action);
        }

        return action;
    }

    /**
     * Replaces the reducer currently used by the store to calculate the state.
     *
     * You might need this if your app implements code splitting and you want to
     * load some of the reducers dynamically. You might also need this if you
     * implement a hot reloading mechanism for Redux.
     *
     * @param {Function} nextReducer The reducer for the store to use instead.
     * @returns {void}
     */
    function replaceReducer(nextReducer) {
        if (typeof nextReducer !== 'function') {
            throw new Error('Expected the nextReducer to be a function.');
        }

        currentReducer = nextReducer;
        dispatch({ type: ActionTypes.INIT });
    }

    // When a store is created, an "INIT" action is dispatched so that every
    // reducer returns their initial state. This effectively populates
    // the initial state tree.
    dispatch({ type: ActionTypes.INIT });

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