Multisite webpack

package.json

{
  "name": "multisite",
  "copyright": "2018",
  "version": "1.0.0",
  "dependencies": {
    "bootstrap-sass": "^3.3.7",
    "jquery": "^2.1.3",
    "wp-admin-custom": "4.9.6"
  },
  "devDependencies": {
    "babel-core": "^6.26.0",
    "babel-loader": "^7.1.2",
    "babel-preset-es2015": "^6.24.1",
    "browser-sync": "^2.23.6",
    "browser-sync-webpack-plugin": "^1.2.0",
    "css-loader": "^0.28.7",
    "extract-text-webpack-plugin": "^3.0.0",
    "file-loader": "^0.11.2",
    "node-sass": "^4.5.3",
    "path": "^0.12.7",
    "sass-loader": "^6.0.6",
    "style-loader": "^0.18.2",
    "webpack": "^3.10.0"
  },
  "scripts": {
    "build": "webpack --progress --env.production -p",
    "watch": "webpack --progress --env.dev --display=minimal --colors --watch"
  },
  "repository": {
    "type": "git"
  },
  "author": "German Pichardo",
  "license": "UNLICENSED",
  "private": true
}

webpack.config.js

'use strict';
const webpack = require('webpack');
const path = require('path');
const ExtractTextPlugin = require('extract-text-webpack-plugin');
const BrowserSyncPlugin = require('browser-sync-webpack-plugin');

const themesPath = path.join(__dirname, 'web/app/themes');
const themeAssets = {
    'base': path.join(themesPath, 'base/assets'),
    'theme_1': path.join(themesPath, 'theme_1/assets'),
    'theme_2': path.join(themesPath, 'theme-2/assets'),
    'theme_3': path.join(themesPath, 'theme-2/assets'),
};

// https://stackoverflow.com/a/45278943
module.exports = function (env, argv) {

    return {
        devtool: env.production ? '' : 'inline-source-map',
        entry: {
            'web/app/themes/theme-1/assets/build/theme': [
                path.join(themeAssets.theme_1, 'js/theme.js'),
                path.join(themeAssets.theme_1, 'scss/theme.scss'),
            ],
            'web/app/themes/theme-2/assets/build/theme': [
                path.join(themeAssets.theme_2, 'js/theme.js'),
                path.join(themeAssets.theme_2, 'scss/theme.scss'),
            ],
            'web/app/themes/theme-3/assets/build/theme': [
                path.join(themeAssets.theme_3, 'js/theme.js'),
                path.join(themeAssets.theme_3, 'scss/theme.scss'),
            ],
        },
        output: {
            filename: '[name].js',
        },
        module: {
            rules: [
                {
                    test: /\.js/,
                    use: [
                        {
                            loader: 'babel-loader'
                        }
                    ]
                },
                {
                    test: /\.scss$/,
                    use: ExtractTextPlugin.extract({
                        fallback: 'style-loader',
                        use: [{
                            loader: 'css-loader',
                            options: {
                                sourceMap: !env.production,
                                minimize: env.production
                            }
                        }, {
                            loader: 'sass-loader',
                            options: {
                                outputStyle: 'expanded', // Build bug (.class-white -> .class-#fff)
                                sourceMap: !env.production
                            }
                        }]
                    })
                },
                {
                    test: /\.(png|jpg|gif|svg|eot|ttf|woff|woff2)$/,
                    loader: 'file-loader',
                    options: {
                        name: '[name].[ext]',
                        useRelativePath: true // TODO: No images treatment ??
                    }
                }
            ]
        },
        externals: {
            $: '$',
            jquery:
                'jQuery'
        },
        plugins: [
            new webpack.optimize.UglifyJsPlugin({
                compress: argv['optimize-minimize'], // only if -p or --optimize-minimize were passed
                sourceMap: !env.production
            }),
            new ExtractTextPlugin('[name].css'),
            new BrowserSyncPlugin({
                // browse to http://localhost:3000/ during development,
                // ./public directory is being served
                proxy: http://localhost:3000/,
                port: 8686,
                files: [
                    '**/*.twig'
                ],
                reloadOnRestart: true
            },
            // plugin options
            {
                reload: true
            })
        ],
        resolve: {
            alias: {
                'base-scss': path.join(themeAssets.base, 'scss'), // TODO verify path in prod
                'base-js': path.join(themeAssets.base, 'js')
            }
        }
    };
};