I love where JS is heading, but perhaps its worth pointing out its a lot easier to rapidly advance a language that historically has been missing huge features.
I'd also argue none are as important as JS. People can choose to not use Ruby, Python or C++, but if you're doing web atm you're pretty much stuck with JavaScript.
All professional languages reach C++'s complexity, which probably is not as complex as PL/I or Algol 68W were for their time.
Python is my favourite example to pick up on this.
Target at beginners and deemed as simple, yet I doubt anyone is able to know Python semantics since version 1.0 and by looking at a random codebase is able to state what is the minimum Python version required to run the code without errors.
Also I very much doubt anyone knows Python's library cover to cover.
Languages get complex because real world has complex needs.
Even Go, the new poster child of simplicity, now has quite a few warts, because not everyone doing software like Google.
Fair enough, and Python is a good example, but I'm guessing Scheme and Smalltalk managed to stay relatively simple over time, although I don't know how much of that would be chalked up to lack of mainstream support.