Create Store function - My own

createStore.js

function createStore(initialState, reducer) {
  let state = initialState;
  let callback = [];
  
  return {
    listen(cb) {
      callback = calback.push(cb);
    },
    dispatch(actionCreator) {
      const newState = reducer(state, actionCreator);
      state = { ...state, ...newState };
      
      callback(state);
    },
    get() { return state; }
  }
}