I just merged some code that makes Haxe/JS output ES6 classes instead of classic Function+prototype. It’s available in latest nightlies (also installable with Lix) and can be activated with the
-D js-es=6 compiler argument.
We decided to include it in already Haxe 4.0, because ES6 class support is becoming critical nowadays, as they are not backwards-compatible with the classic inheritance style, making it impossible to use some ES6 libraries with Haxe.
We might look into adding more ES6 features usage for future versions, and meanwhile, the bravest ones are welcome to give it a try and give feedback!
UPD: I just wrote some documentation on this, describing limitations and required workarounds. Hopefully that will be part of the Haxe Manual soon enough!