The core Redux createStore library

redux.js

const createStore = (reducer, initialState) => {
  const store = {};
  store.state = initialState;
  store.listeners = [];
  
  store.getState = () => store.state;
  
  store.subscribe = (listener) => {
    store.listeners.push(listener);
  };
  
  store.dispatch = (action) => {
    store.state = reducer(store.state, action);
    store.listeners.forEach(listener => listener());
  };
  
  return store;
};