尝试得到react-router (v4.0.0)和react-hot loader (3.0.0-beta.6)很好地发挥,但在浏览器控制台得到以下错误:

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;

当前回答

所以我遇到了这个问题,我用一种奇怪的方式解决了它。我想我应该把它扔了,以防其他人遇到它,变得绝望。

我有一个有条件地呈现react元素,它只在对象状态大于零时才会呈现。在呈现函数中-当三元运算符被证明为真时,我收到了这篇文章所涉及的错误。我使用了一个<React。片段>在我的渲染函数-这是我通常分组子的方式,而不是更新的方式与更新的短语法(<>和</>)。

However, when I changed the <React.Fragment> to the short syntax - the react element rendered correctly and the error stopped appearing. I took a look at Facebooks React-Fragment documentation, and I don't see any reason on there to believe there is a dramatic difference between the two that would cause this. Regardless, below are two simplified snippets of code for your review. The first one demonstrates the code that was yielding the error, and the second one demonstrates the code that fixed the issue. At the bottom is the render function of the component itself.

希望有人觉得这有帮助。

代码示例1 -错误 有条件渲染的React元素


  renderTimeFields = () => {
    return (
      <React.Fragment>
        <div className="align-left">
                <div className="input-row">
                  <label>Date: </label>
                  <input type="date" className="date" name="date" min={new Date().toISOString().split('T')[0]} required/>
                </div>
              </div>
              <div className="align-left sendOn-row">
                <div className="input-row">
                  <label>Time: </label>
                  <input type="time" className="time" name="time" required/>
                </div>
              </div>
      </React.Fragment>
    );
  }

代码示例2 -无错误 有条件渲染的React元素


  renderTimeFields = () => {
    return (
      <>
        <div className="align-left">
                <div className="input-row">
                  <label>Date: </label>
                  <input type="date" className="date" name="date" min={new Date().toISOString().split('T')[0]} required/>
                </div>
              </div>
              <div className="align-left sendOn-row">
                <div className="input-row">
                  <label>Time: </label>
                  <input type="time" className="time" name="time" required/>
                </div>
              </div>
      </>
    );
  }

在组件中呈现函数

render() {
<form>
...
{emailsInActiveScript > 1 ? this.renderTimeFields() : null}
</form>
etc...
}

其他回答

在我的例子中,创建组件和渲染的顺序很重要。我在创建组件之前渲染了它。最好的方法是创建子组件,然后是父组件,然后呈现父组件。改变顺序为我解决了这个问题。

在我的情况下,我只需要从react-router-redux升级到react-router-redux@next。我猜肯定是兼容性问题。

这真的很简单。当我开始编写React时,我遇到了这个问题,这个问题几乎总是因为导入:

import React, { memo } from 'react';

你可以对它进行解构,因为react lib有一个memo属性,但你不能这样解构

import { user } from 'assets/images/icons/Profile.svg';

因为它不是一个对象。

希望能有所帮助!

当我将nothingundefined作为值传递给我创建的子组件时,发生了这个问题。我做了这个<MyComponent src="" />导致错误。然后将其更改为<MyComponent src=" " />,因为我真的不想传递任何东西…问题解决了。

您需要了解命名导出和默认导出。我什么时候应该用大括号导入ES6 ?

在我的例子中,我通过改变

import Provider from 'react-redux'

to

import { Provider } from 'react-redux'