> none of the new features are very optimized I think for-of is getting pretty good. It's a bit of a pain to optimize because the iteration protocol in ES6 is

> none of the new features are very optimized I think for-of is getting pretty good. It's a bit of a pain to optimize because the iteration protocol in ES6 is designed in such a way that you have to do heroics (scalar replacement) to have any hope of optimizing it well. But engines are getting there.