Then why not use something like https://6to5.org/ ? Most syntax features can be ...

thejameskyle on Jan 2, 2015 | parent | context | favorite | on: ECMAScript 6: new OOP features besides classes

Then why not use something like https://6to5.org/ ? Most syntax features can be transpiled without a runtime (generators being an exception) and everything else can simply use polyfills.