webpack.config.js

const webpack = require('webpack');
const path = require('path');
const ExtractTextPlugin = require('extract-text-webpack-plugin');

process.env.NODE_ENV = process.env.NODE_ENV || 'development';

if (process.env.NODE_ENV === 'test') {
    require('dotenv').config({ path: '.env.test' });
} else if (process.env.NODE_ENV === 'development') {
    require('dotenv').config({ path: '.env.development' });
}
module.exports = (env) => {
    const isProduction = env === 'production'; // this is set in the package.json script with the --env production flag
    const CSSExtract = new ExtractTextPlugin('styles.css');
    return {
        entry: ['babel-polyfill', './src/app.js'], // babel polyfill enables much better browser compatibility
        // entry:"./src/playground/add-array.js",
        output: {
            path: path.join(__dirname, 'public', 'dist'),
            filename: 'bundle.js'
        },
        module: {
            rules: [
                {
                    loader: 'babel-loader',
                    test: /\.js$/,
                    exclude: /node_modules/
                },
                {
                    test: /\.s?css$/,
                    use: CSSExtract.extract({
                        use: [
                            {
                                loader: 'css-loader',
                                options: {
                                    sourceMap: true
                                }
                            },
                            {
                                loader: 'sass-loader',
                                options: {
                                    sourceMap: true
                                }
                            }

                        ]
                    })
                }
            ]
        },
        plugins: [
            CSSExtract,
            new webpack.DefinePlugin({ // This will create a webpack "variable" that can be referred to, thus allowing these keys to change based on the environment and not having expose files with keys?
                'process.env.FIREBASE_API_KEY': JSON.stringify(process.env.FIREBASE_API_KEY),
                'process.env.FIREBASE_AUTH_DOMAIN': JSON.stringify(process.env.FIREBASE_AUTH_DOMAIN),
                'process.env.FIREBASE_DATABASE_URL': JSON.stringify(process.env.FIREBASE_DATABASE_URL),
                'process.env.FIREBASE_PROJECT_ID': JSON.stringify(process.env.FIREBASE_PROJECT_ID),
                'process.env.FIREBASE_STORAGE_BUCKET': JSON.stringify(process.env.FIREBASE_STORAGE_BUCKET),
                'process.env.FIREBASE_MESSAGING_SENDER_ID': JSON.stringify(process.env.FIREBASE_MESSAGING_SENDER_ID)
            })
        ],
        devtool: isProduction ? 'source-map' : 'inline-source-map',
        devServer: {
            contentBase: path.join(__dirname, 'public'),
            publicPath: '/dist/',
            historyApiFallback: true /// reroute 404s to index.html (which will handle routing)
        }
    };
};