[dickson]

Tail recursion optimization, lazy evaluation

[sabarjp]

Tail recursion optimization is in ES6. Lazy Evaluation is provided in multiple libraries, including lazy.js.

There are also several libraries with pure functional implementations (ex: bilby)

[Lazare]

If you're listing a core language feature as something that "can't be done in that language", you may not understand the language as well as you think.