Understand Redux in 5 minutes

redux-in-5-minutes.js

export class Store {
    constructor(executor, initialState = {}) {
        this.subscribers = [];

        this.state = initialState;
        // function that executes reducer or combined reducers  and returns the new state
        this.executor = executor;
    }
    notifySubscribers() {
        for (let i = 0; i < this.subscribers.length; i++) {
            this.subscribers[i]();
        }
    }
    getState() {
        return this.state;
    }
    dispatch(actionResult) {
        this.state = this.executor(this.state, actionResult);
        this.notifySubscribers();
    }
    subscribe(fn) {
        this.subscribers.push(fn);
    }
}

export function createStore(reducerOrCombinedReducers, initialState) {
    return new Store((state, actionResult) => {
        // returns the new state with reducer function or combined reducer function
        return reducerOrCombinedReducers(state, actionResult);
    }, initialState);
}

export function combineReducers(reducerObject) {
    // returns a function that executes all reducers
    return (state, actionResult) => {
        // executes all reducers and return the new state
        let newState = {};
        for (let type in reducerObject) {
            if (reducerObject.hasOwnProperty(type)) {
                let reducer = reducerObject[type];
                newState[type] = reducer(state[type], actionResult);
            }
        }
        return newState;
    };
}