webpack.config.js

// Need to define Entry point
// Define location for output file

const path = require('path')
const webpack = require('webpack')
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'
    console.log('env', env)
    return {
        entry:["@babel/polyfill", './src/app.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: [
                        'style-loader',
                        'css-loader',
                        'sass-loader'
                    ]
                }
            ]
        },
        plugins: [
            new webpack.DefinePlugin({
                '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),
                'process.env.FIREBASE_API_ID': JSON.stringify(process.env.FIREBASE_API_ID)
            })
        ],
        devtool: isProduction ? 'source-map' : 'cheap-module-eval-source-map',
        devServer: {
            contentBase: path.join(__dirname, 'public'),
            historyApiFallback: true,
            publicPath: '/dist/'
        }
    }
}