Yes, JS certainly is that (or comes close), which is the thing I like the most about JS and miss the most in Lisp - so much so that I wrote macros to allow me t

Yes, JS certainly is that (or comes close), which is the thing I like the most about JS and miss the most in Lisp - so much so that I wrote macros to allow me to use JS-style objects wherever possible. (I don't mean JS-style OO, which I avoid at all costs. Hate "this" and "prototype", love "a.b" and "a[b]".) The benefit of the hashmap for exploratory programming is so great that it raises the question of whether a fully regular/metaprogrammable Lisp could be evolved from it. Not clear if it would be practical, or add anything of value, but if it did it would be interesting.