最简单的 redux 实现

https://redux.js.org/introduction/getting-started
题目：根据官网上的例子来一个极简实现。只需要实现相同的输出即可

export const createStore = (reducer) => {
  let state = undefined;
  let subscribeFn = () => {};
  const subscribe = (fn) => {
    subscribeFn = fn;
  };
  const dispatch = (action) => {
    state = reducer(state, action);
    subscribeFn();
  };
  const getState = () => state;
  return {
    subscribe,
    dispatch,
    getState,
  };
};