Here is an interesting article about the downsides of using modern JavaScript for production. To be sure that we can use modern notation we would need an integrated Babel conversion or at least some sort of Babel post processing. On the other hand, using Babel can significantly bloat your source. The article points out some constructs to watch out for…
In case of Hype (specially with extensions) it’s worth considering notation and the implications.
In case of the extensions I publish the minified versions are processed with Closure Compiler but I anyway avoid unnecessary modern notation to keep bloat down and compability up.
There is an online compiler here:
https://closure-compiler.appspot.com/