I am getting this error. I have defined all components in index.js and I am using react-dom.

Webpacker本身在编译时没有错误或警告。

错误：未捕获的错误：元素类型无效：应为字符串（对于内置组件）或类/函数（对于复合组件）但得到：未定义。您可能忘记从它在index.js 中定义的文件中导出您的组件

import 'core-js/fn/object/assign';
import React, { Component }  from 'react';
import ReactDOM from 'react-dom';
import { App } from './components/CustomerSearch';


// Render the main component into the dom
ReactDOM.render(<App />, document.getElementById('app'));

应用组件.js

import React, { Component }  from 'react';
import {Grid} from 'Adding my own package here';
import EventEmitter from 'wolfy87-eventemitter';


export default class AppComponent extends React.Component {

  emitter = null;

  constructor() {
    super();

    this.emitter = new EventEmitter();

    this.emitter.addListener('result', function (args) {
    })

  }

  render() {
    return (
      <div className="Search">
        <Grid>
          <Grid.Column width={4}>
            <SearchForm updatechForm emitter={this.emitter}/>
          </Grid.Column>
          <Grid.Column width={12}>
            <ResultList emitter={this.emitter}/>
          </Grid.Column>
        </Grid>
      </div>
    );
  }
}

AppComponent.defaultProps = {};

错误

warning.js:35 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.
printWarning @ warning.js:35
warning @ warning.js:59
createElement @ ReactElementValidator.js:192
(anonymous) @ index.js:7
__webpack_require__ @ bootstrap 35891eb36bf51eb82cc9:19
module.exports @ bootstrap 35891eb36bf51eb82cc9:62
(anonymous) @ bootstrap 35891eb36bf51eb82cc9:62
invariant.js:44 Uncaught Error: Element 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.
    at invariant (invariant.js:44)
    at ReactCompositeComponentWrapper.instantiateReactComponent [as _instantiateReactComponent] (instantiateReactComponent.js:74)
    at ReactCompositeComponentWrapper.performInitialMount (ReactCompositeComponent.js:366)
    at ReactCompositeComponentWrapper.mountComponent (ReactCompositeComponent.js:257)
    at Object.mountComponent (ReactReconciler.js:45)
    at mountComponentIntoNode (ReactMount.js:104)
    at ReactReconcileTransaction.perform (Transaction.js:143)
    at batchedMountComponentIntoNode (ReactMount.js:126)
    at ReactDefaultBatchingStrategyTransaction.perform (Transaction.js:143)
    at Object.batchedUpdates (ReactDefaultBatchingStrategy.js:62)