redux CreateStore

createStore.js

const createStore = (reducer) => {
  let state;
  let listeners = [];
  
  const getState = () => {
    return 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 { getState, dispatch, subscribe };
}