const createStore = (reducer,presetState, enhancer) =>  {
      if (typeof presetState === "function") {
          enhancer = presetState         presetState = undefined     }     if (typeof enhancer === 'function') {
         return enhancer(createStore)(reducer,presetState)     }      if (typeof reducer  !== "function") {
           throw new Error('传入的reducer不是一个函数')      }     let state = presetState     let listeners = []     const getState = () => state     const dispatch = (action) => {
        state =  reducer(state, action)         listeners.forEach(item => item())     }     const subscribe = (fn) => {
          listeners.push(fn)     }     dispatch({type:'@@react/Init'})     return {
          getState,         dispatch,         subscribe     } }