A big part of my thesis was going to involve the implementation of a JIT compiler for some dynamic language, and so our discussion rapidly became focused on which language I should be working with. It was a good compromise: a widely-used "real-world" programming language, warts and all, that was still small enough for one person to realistically implement a compiler for. There are a number of semantic inconsistencies in JavaScript that need fixing, but the ES6 and ES7 additions do nothing to fix those, they merely add new features (read: complexity) to the language.