“composeEnhancers” 不是 ReactJS 中的函数

Question

我的代码中出现以下错误：

TypeError: composeEnhancers is not a function

const store = createStore(rootReducer, composeEnhancers(
    applyMiddleware(thunk)
));

任何人都可以看到问题出在这里吗？我不明白，因为我刚刚复制了我的 ReactJS 讲师的代码，他没有收到此错误，但我确实收到了。

我的整个代码显示在这里：

import React from 'react';
import ReactDOM from 'react-dom';
import { BrowserRouter } from 'react-router-dom';
import { Provider } from 'react-redux';
import { createStore, applyMiddleware, compose, combineReducers } from 'redux';
import thunk from 'redux-thunk';

import './index.css';
import App from './App';
import registerServiceWorker from './registerServiceWorker';
import burgerBuilderReducer from './store/reducers/burgerBuilder';
import orderReducer from './store/reducers/order';
import authReducer from './store/reducers/auth';

const composeEnhancers = process.env.NODE_ENV === 'development' ? window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ : null || compose;

const rootReducer = combineReducers({
    burgerBuilder: burgerBuilderReducer,
    order: orderReducer,
    auth: authReducer
});

const store = createStore(rootReducer, composeEnhancers(
    applyMiddleware(thunk)
));

const app = (
    <Provider store={store}>
        <BrowserRouter>
            <App />
        </BrowserRouter>
    </Provider>
);

ReactDOM.render( app, document.getElementById( 'root' ) );
registerServiceWorker();

更具描述性的错误（在浏览器的控制台中）显示：

Uncaught TypeError: composeEnhancers is not a function
    at Object../src/index.js (index.js:23)
    at __webpack_require__ (bootstrap 2dae6e05073e9d71bfd6:698)
    at fn (bootstrap 2dae6e05073e9d71bfd6:111)
    at Object.0 (order.js:59)
    at __webpack_require__ (bootstrap 2dae6e05073e9d71bfd6:698)
    at bootstrap 2dae6e05073e9d71bfd6:796
    at bootstrap 2dae6e05073e9d71bfd6:796

Answer 1

您可能在未安装 Redux DevTools 的浏览器中以开发模式运行您的应用程序。

问题出在这一行：

const composeEnhancers = process.env.NODE_ENV === 'development' ? window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ : null || compose;

由于运算符优先级规则，这等效于：

const composeEnhancers = process.env.NODE_ENV === 'development' ? window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ : (null || compose);

或者，如果您更喜欢：

let composeEnhancers = null;
if (process.env.NODE_ENV === 'development') {
    composeEnhancers = window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__;
} else {
    composeEnhancers = compose;
}

因此，如果您处于开发模式并且您的浏览器中没有安装 Redux DevTools 扩展，您的应用程序将会中断，因为window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__未定义。你真正需要的是：

let composeEnhancers = null;
if (process.env.NODE_ENV === 'development') {
    composeEnhancers = window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ || compose;
} else {
    composeEnhancers = compose;
}

或者，更简单地说：

const composeEnhancers = (process.env.NODE_ENV === 'development' ? window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ : null) || compose;