我试图做reduxer（学习）的基本测试，它似乎基本没有问题，但我得到这个错误”×错误：在初始化期间，Reducer“counter”返回未定义的值。如果传递给Reducer的状态未定义，则必须显式返回初始状态。初始状态可能未定义。如果不想为此Reducer设置值，则可以使用null而不是undefined。
我相信回应是非常愚蠢的希望得到帮助。
Reduxer文件. counter.js

const counterReducer = (state = 0, action) => {
  switch (action.type) {
    case "INCREMENT":
      return state + 1;
    case "DECREMENT":
      return state - 1;
  }
};

export default counterReducer;

isLogged.js

const loggedReducer = (state = false, action) => {
  switch (action.type) {
    case "SING_IN":
      return !state;
    default:
      return state;
  }
};
export default loggedReducer;

索引. js

import counterReducer from "./counter";
import loggedReducer from "./isLogged";
import { combineReducers } from "redux";

const allReducers = combineReducers({
  counter: counterReducer,
  isLogged: loggedReducer,
});

export default allReducers;

src文件夹〉index.js.

import React from "react";
import ReactDOM from "react-dom";
import "./index.css";
import App from "./App";
import * as serviceWorker from "./serviceWorker";
import { createStore } from "redux";
import allReducer from "./reducers";

const store = createStore(
  allReducer,
  window.__REDUX_DEVTOOLS_EXTENSION__ && window.__REDUX_DEVTOOLS_EXTENSION__()
);

ReactDOM.render(
  <React.StrictMode>
    <App />
  </React.StrictMode>,
  document.getElementById("root")
);

serviceWorker.unregister();