webpack-dev-server, historyApiFallback not working

I am testing out react-router4 with webpack4, but I can't get webpack-dev-server's setting:

{historyApiFallback: true}

to work. This use to work just fine in webpack3, so I am not sure what is wrong... Here is my webpack.config.js:

const HtmlWebpackPlugin = require('html-webpack-plugin');

module.exports = () => {
  return {
    mode: 'development',
    devtool: 'source-map',
    devServer: {
      port: 8888,
      historyApiFallback: true,
      stats: 'minimal'
    },
    resolve: {
      extensions: ['*', '.mjs', '.js', '.jsx']
    },
    module: {
      rules: [
        {
          test: /\.m?jsx?$/,
          exclude: /(node_modules)/,
          use: {
            loader: 'babel-loader'
          }
        }
      ]
    },
    plugins: [
      new HtmlWebpackPlugin({
        title:'React Lab',
        template: 'src/index.html'
      })
    ]
  }
}

and here is my simple react app with react-router4:

import React from 'react';
import ReactDOM  from 'react-dom';
import {
  BrowserRouter as Router,
  Route,
  Link,
  Switch
} from 'react-router-dom';

const mountNode = document.getElementById('app');

const App = () => (
  <Router>
    <div>

      <ul>
        <li><Link to="/">Link to: /</Link></li>
        <li><Link to="/page1">Link to: /page1</Link></li>
        <li><Link to="/page2">Link to: /page2</Link></li>
        <li><Link to="/does/not/exist">Link to: /does/not/exist</Link></li>
      </ul>
      <button onClick={()=>{location.reload();}}>reload page</button>

      <Switch>
        <Route exact path="/"      component={()=>(<h2>home</h2>)} />
        <Route exact path="/page1" component={()=>(<h2>page1</h2>)} />
        <Route exact path="/page2" component={()=>(<h2>page2</h2>)} />
        <Route                     component={()=>(<h2>no match</h2>)} />
      </Switch>

      <Route path="/" component={(props) =><div>{`props.location.pathname: ${props.location.pathname}`}</div>} />

    </div>
  </Router>
);

ReactDOM.render( <App/>, mountNode

After navigating to:

<Link to="/does/not/exist" />

and click

<button>reload page</button>

webpack dev server fail to redirect to main.js

Here is the complete code at github: https://github.com/ApolloTang/webpack-dev-server-history-api-fall-back-not-working.

Any help or comment would greatly appreciated.

It turns out that I am missing output.publicPath in webpack.config.js:

output: {
  //  must specified output.publicPath otherwise
  //  devServer.historyApiFallback will not work
  publicPath: '/'
},

with output.publicPath specified as above, historyApiFallback works.

I can't remember where I have read that said output.publicPath is an optional in webpack4's configuration, but it does required to work with webpack-dev-server.

The documentation at https://webpack.js.org/configuration/output/#output-publicpath said: