[javascript] ES6

There **needs** to be ES6. Anyone working on that already?

I'm not too sure though if this should be treated as a separate language or go as an addendum to JavaScript (will probably break the runnable example rule)?

The issue requests ES6 support but names no file, test, or entry point. First clarify whether ES6 belongs in the JavaScript document or a separate language document, then define the runnable-example scope and acceptance criteria before implementation.

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