Identify used Magento 2 frontend extensions in a Luma install

identify.php

<?php

// Run with the URL pointing to a require-config.js as the first argument;
// php identify.php http://magento2demo.firebearstudio.com/pub/static/frontend/Magento/luma/en_US/requirejs-config.js

$content = file_get_contents($argv[1]);
preg_match_all(
  '/(?P<quote>\'|")(?P<extension>[[:alnum:]]+_[[:alnum:]]+)\/js\/.+?(?P=quote)/m',
  $content,
  $matches
);

sort($matches['extension']);

print_r(array_unique($matches['extension']));

Javascript version you can use in your console on a Magento2 site (with RequireJS)

[...new Set(Object.entries(requirejs.s.contexts._.config.map['*']).filter(path => path[1].includes('') && path[1].includes('/js/')).map(path => path[1].split('/')[0]).sort())]