Javascript plugin and environment variables
Here's one way to do it...
First create a custom webpack.config.js at src/Resources/app/storefront/build. Also in that build directory run npm install dotenv, as you will need it to parse your .env file.
Your webpack.config.js could then look like this:
const fs = require('fs');
const dotenv = require(`${__dirname}/node_modules/dotenv/lib/main.js`);

module.exports = () => {
    // given you `.env` is located directly in your plugin root dir
    const contents = fs.readFileSync(`${__dirname}/../../../../../.env`);
    const config = dotenv.parse(contents);

    return {
        externals: {
            myPluginEnv: JSON.stringify(config),
        }
    };
};

Then inside your sources you can import myPluginEnv.
import * as myPluginEnv from 'myPluginEnv';

/*
 * Example .env content:
 * FOO=1
 * BAR=1
 */

console.log(myPluginEnv);
// {FOO: '1', BAR: '1'}


I was reading the documentation here https://developer.shopware.com/docs/guides/plugins/plugins/storefront/add-custom-javascript but cannot find a mention on how to make usage of environment variables in a  javascript plugin.
Currently I tried to put a .env file at the root of my plugin in custom/apps/MyPlugin/.env and to capture them via process.env but it fallbacks to my default values...
Is there a way to handle a .env file when you run bash bin/build-storefront.sh?
Thanks.
