gistfile1.txt

const webpack = require('webpack');
const path = require('path');
let root = path.resolve(__dirname);

module.exports = {
    mode: 'development',
    devServer: {
        disableHostCheck: true,
        host: 'localhost',
        port: 4001,
        https: false,
        historyApiFallback: true, 
        hot: true,
        inline: true,
        compress: true,
    },
    entry: [
        'babel-polyfill',
        'react-hot-loader/patch',
        'webpack/hot/only-dev-server',
        path.join(process.cwd(), 'src/index.js')
    ],
    output: {
        path: path.resolve(__dirname, './public'),
        filename: 'bundle.js'
    },
    module: {
        rules: [
            {
                test: /\.(woff2?|svg)$/,
                loader: 'url-loader?limit=10000'
            },
            {
                test: /\.(ttf|eot)$/,
                loader: 'file-loader'
            },
            {
                test:   /\.css$/,
                loaders: ['style-loader', 'css-loader']
            },
            {
                test: /\.scss$/,
                loaders: ['style-loader', 'css-loader', 'sass-loader']
            },
            {
                test: /.(png|woff(2)?|eot|ttf|svg)(\?[a-z0-9=\.]+)?$/,
                loader: 'file-loader?name=[hash].[ext]'
            },
            {
                test: /\.(js|jsx)$/,
                loader: require.resolve('babel-loader'),
                options: {
                    cacheDirectory: true,
                    plugins: ['react-hot-loader/babel'],
                },
                exclude: /(node_modules)/,
                include: root
            }
        ]
    },
    cache: true,
    devtool: 'cheap-module-eval-source-map',
    plugins:[
        new webpack.HotModuleReplacementPlugin()
    ]
};

gistfile2.txt

import ReactDOM from 'react-dom';
import React from 'react';
import { AppContainer } from 'react-hot-loader';
import App from './app';

const render = Component => {
    ReactDOM.render(
      <AppContainer>
        <Component />
      </AppContainer>,
      document.getElementById('app'),
    )
}

render(App);

if (module.hot) {
  module.hot.accept('./app.js', () => {
    const NextRootContainer = require('./app.js').default;
    render(<NextRootContainer />, document.getElementById('react-root'));
  })
}