Your Sass styles are compiled to Css using Dart Sass and then minified using Csso.

let compiled = sass.compile(filepath)
let minified = csso.minify(compiled.css).css
fs.writeFileSync(outpath, minified)

Your JavaScript is minified using jsmin and it's default Crockford's algorithm.

let minified = jsmin(fs.readFileSync(filepath, 'utf8'))
fs.writeFileSync(outpath, minified)