webpack.config.js

var path = require('path');
module.exports = {
    entry: './src/index.js',
    mode: 'production',
    output: {
        path: path.resolve(__dirname, 'build'),
        filename: 'index.js',
        libraryTarget: 'commonjs2'
    },
    module: {
        rules: [
            {
                test: /\.js?$/,
                exclude: /(node_modules)/,
                use: 'babel-loader',
            },
            {
                test: /\.css$/,
                use: [
                    'style-loader',
                    'css-loader'
                ]
            }
        ],
    },
    resolve: {
        alias: {
            'react': path.resolve(__dirname, './node_modules/react'),
            'react-dom': path.resolve(__dirname, './node_modules/react-dom'),
        },
        fallback: {
             "stream": require.resolve("stream-browserify")
        }
    },
    externals: {
        'react': 'commonjs react'
    }
};