Laravel mix, how to pass variable while mixing?

So I have a JS file that I want to mix and copy and compress using Laravel mix, my webpack.mix.js file looks like so:

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

    mix.js('resources/js/foo/foo.js', 'public/foo.js');
    mix.copy('public/foo.js', 'public/js/foo.js');
    mix.version();

The thing is that foo.js has a variable called env which is set to dev on local envs and we set it to app on production.

Is there a way I can automate this? Can I pass the variable according to the env while mixing the file and set this?

via Chebli Mohamed