[tachyonbeam]

As a compiler writer, I can tell you that in JS, local variable lookups do not incur any kind of dynamic overhead. The performance of modern JS engines is much closer to C than you might think. Dynamic language optimization is also not so recent. Most of the techniques implemented by modern JS engines were invented for the Smalltalk and Self projects. See this paper from 1991, for example: http://bibliography.selflanguage.org/_static/implementation....

Python is just inexcusably non-optimized. It's a bytecode interpreter, with each instruction requiring dynamic dispatch. Integers are represented using actual objects, with pointer indirection. The most naive, non-optimizing JIT implementation might get you a 10x speedup over CPython. I think that eventually, as better-optimised dynamic languages gain popularity, people will come to accept that there is no excuse for dynamic language implementations to perform this poorly.

[klmr]

I haven’t followed recent development of JavaScript all that closely so my knowledge is somewhat outdated. However, the optimisations that make JS performance close to C in some cases are really recent. Some of the tricks are old, such as the paper you cited. But these tricks only go so far, and in particular even modern GCs simply work badly in memory-constrained environments, which puts a hard upper limit on the amount of memory that JavaScript can handle efficiently. One of the better articles on this subject is [1].

That said, my comment already mentioned that local variable lookup isn’t a problem in JavaScript. It is in R, however; see my example in [2]. Beyond that, both R and Python execution have obvious optimisation potential, which is made hard by the fact that existing libraries rely extensively on implementation details of the current interpreters.

[1] http://sealedabstract.com/rants/why-mobile-web-apps-are-slow...

[2] https://news.ycombinator.com/item?id=11117070