Luckily, that's not correct.

Just pipe your JavaScript into Closure and it will minify it as easily as Uglify. We're migrating to Webpack, but we've been using this for about 4 years:

    node_modules/.bin/browserify index.js | closure-compiler \
      --warning_level quiet \
      --third_party \
      --jscomp_off es3 \
      --compilation_level SIMPLE_OPTIMIZATIONS \
      --language_in ECMASCRIPT5 \
      --create_source_map "index.min.js.map" \
      --output_wrapper "%output%//# sourceMappingURL=/index.min.js.map" \
      > index.min.js

This generates a minified file plus a source map.

Part of the magic happens in Browserify [1], which generates a single file from all your inputs, taking care to follow the import chains in the correct order. If you have ES6 code, you'll just install Babel and add "-r babel-register" to the Browserify command line.

I read the rant in your other comment, and I don't understand what it was that you struggled with. You certainly don't need to follow Google's Closure conventions in order for it to optimize and minify your code effectively. We don't; we use React and Babel with all the ES6 bells and whistles, but none of the Google conventions.

[1] http://browserify.org