a really skinned version of createStore

createStore.js

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