React.createElement:类型无效——需要一个字符串 [英] React.createElement: type is invalid -- expected a string

问题描述

尝试让 react-router (v4.0.0) 和 react-hot-loader (3.0.0-beta.6) 运行良好，但在浏览器控制台中出现以下错误:

Trying to get react-router (v4.0.0) and react-hot-loader (3.0.0-beta.6) to play nicely, but getting the following error in the browser console:

Warning: React.createElement: type is invalid -- expected a string
(for built-in components) or a class/function (for composite
components) but got: undefined. You likely forgot to export your
component from the file it's defined in.

index.js:

import React from 'react';
import ReactDom from 'react-dom';
import routes from './routes.js';
require('jquery');
import 'bootstrap/dist/css/bootstrap.min.css';
import 'bootstrap/dist/js/bootstrap.min.js';
import './css/main.css';

const renderApp = (appRoutes) => {
    ReactDom.render(appRoutes, document.getElementById('root'));
};

renderApp( routes() );

routes.js:

import React from 'react';
import { AppContainer } from 'react-hot-loader';
import { Router, Route, browserHistory, IndexRoute } from 'react-router';
import store from './store/store.js';
import { Provider } from 'react-redux';
import App from './containers/App.jsx';
import Products from './containers/shop/Products.jsx';
import Basket from './containers/shop/Basket.jsx';

const routes = () => (

    <AppContainer>
        <Provider store={store}>
            <Router history={browserHistory}>
                <Route path="/" component={App}>
                    <IndexRoute component={Products} />
                    <Route path="/basket" component={Basket} />
                </Route>
            </Router>
        </Provider>
    </AppContainer>

);

export default routes;

推荐答案

大多数情况下这是由于导出/导入不正确造成的.

Most of the time this is due to an incorrect export/import.

常见错误:

// File: LeComponent.js
export class LeComponent extends React.Component { ... }

// File: App.js
import LeComponent from './LeComponent';

可能的选择:

// File: LeComponent.js 
export default class LeComponent extends React.Component { ... }

// File: App.js
import LeComponent from './LeComponent';

有几种方法可能会出错，但该错误是由于每次 60% 的导入/导出不匹配造成的.

There are a few ways it could be wrong, but that error is because of an import/export mismatch 60% of the time, everytime.

编辑

通常，您应该获得一个堆栈跟踪，指示故障发生的大致位置.这通常紧跟在您在原始问题中收到的消息之后.

Typically you should get a stacktrace that indicates an approximate location of where the failure occurs. This generally follows straight after the message you have in your original question.

如果它没有显示，则可能值得调查原因(这可能是您缺少的构建设置).无论如何，如果它没有显示，唯一的做法就是缩小导出/导入失败的位置.

If it doesn't show, it might be worth investigating why (it might be a build setting that you're missing). Regardless, if it doesn't show, the only course of action is narrowing down where the export/import is failing.

遗憾的是，没有堆栈跟踪的唯一方法是手动删除每个模块/子模块，直到您不再收到错误为止，然后按自己的方式返回堆栈.

Sadly, the only way to do it, without a stacktrace is to manually remove each module/submodule until you don't get the error anymore, then work your way back up the stack.

编辑 2

通过评论，确实是导入问题，特别是导入了一个不存在的模块

Via comments, it was indeed an import issue, specifically importing a module that didn't exist

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