createStore

createStore.js

const createStore = (reducer) => {
let state;
let listeners = [];
const getState = () => state;

const dispatch = (action) => {
    state = reducer(state, action);
    listeners.forEach(listener => listener());
}

const subscribe = (listener) => {
    listeners.push(listener);

    return () => {
        listeners = listeners.filter(l => l !== listener);
    };
}

dispatch({});

return { dispatch, getState, subscribe };
}