Problem using api key stored on .env using .js file

Hello, I have a google API key on my .env file

MIX_GOOGLE_GEOCODER_API_KEY=MYAPIKEY

I have added on webpack.mix.js the .js file

const mix = require('laravel-mix');

/*
 |--------------------------------------------------------------------------
 | Mix Asset Management
 |--------------------------------------------------------------------------
 |
 | Mix provides a clean, fluent API for defining some Webpack build steps
 | for your Laravel applications. By default, we are compiling the CSS
 | file for the application as well as bundling up all the JS files.
 |
 */

mix.js('resources/js/app.js', 'public/js')
    .postCss('resources/css/app.css', 'public/css', [
        require('postcss-import'),
        require('tailwindcss'),
    ]);

if (mix.inProduction()) {
    mix.version();
}

mix.minify([
    'public/js/maps/franchise-map.js',
    'public/css/maps/franchise-map.css'
])
    .version();

In the franchise-map.js file I have added this

let googleGeoCoderProvider = L.Control.Geocoder.google({
    apiKey: process.env.MIX_GOOGLE_GEOCODER_API_KEY,
});

then, I ran the command npm run production and the command artisan optimize for clear all caches, but I have this error on my console browser

Uncaught ReferenceError: process is not defined
    at franchise-map.min.js?id=988e151f438d0d767bff:13:13

I'm using laravel 8

where is the problem?