使用create-react-app和react-loadable进行代码拆分不起作用

我关注了多篇文章，尤其是这些...

• Create React App中的代码拆分
• react-loadable / README.md

这是代码拆分的示例-getRoutes()在组件的render方法中调用：

// Edit: commented out original `Loadable` abstraction to use standard `Loadable`

import React from 'react'
// import L from 'react-loadable'
import Loadable from 'react-loadable'
import { BrowserRouter, Route, Switch } from 'react-router-dom'

import { LoadingIndicator } from '../components'

// const Loadable = opts =>
//   L({
//     loading: LoadingIndicator,
//     delay: 300,
//     ...opts
//   })

const AuthenticateContainer = Loadable({
  loading: LoadingIndicator,
  loader: () => import(/* webpackChunkName: "auth" */ '../containers/Authenticate')
})

...

export default function getRoutes (isAuthed, browserHistory) {

  return (
    <BrowserRouter>
      <Switch>
        <Route path="/auth" component={AuthenticateContainer} />
        ...
      </Switch>
    </BrowserRouter>
  )
}

..但我的代码未拆分：

$ npm run build

> [email protected] build /path/to/my-app
> bash -ac '. .env.production; react-scripts build'

Creating an optimized production build...

File sizes after gzip:

  854.84 KB (+4 B)  build/static/js/main.1aa92927.js
  17.53 KB          build/static/css/main.36b767d9.css

The bundle size is significantly larger than recommended.
Consider reducing it with code splitting: https: // goo.gl/9VhYWB
You can also analyze the project dependencies: https: // goo.gl/LeUzfb

The project was built assuming it is hosted at the server root.
You can control this with the homepage field in your package.json.
For example, add this to build it for GitHub Pages:

  "homepage" : "http: // myname.github.io/myapp",

The build folder is ready to be deployed.
You may serve it with a static server:

  yarn global add serve
  serve -s build

Find out more about deployment here:

  http: // bit.ly/2vY88Kr

如您所见，构建结果不是分块的，而是单个JS文件。

我究竟做错了什么？

当前使用的版本：

react-scripts: 1.1.4
react-router-dom: 4.3.1
webpack: 3.8.1
npm: 6.1.0