V8 does precompilation to native code and JIT optimization, which can typically turn numerical computations into efficient, and often highly optimized, machine code. These benchmarks seem to primarily be testing algorithms which require a lot of numerical computation and can take advantage of Javascript's typed arrays, which V8 is designed specifically to optimize.
A somewhat more fair comparison would be V8 vs. PyPy, Rubinius/RuJIT, HHVM, and LuaJIT. LuaJIT and V8 would likely still come out on top due to the amount of work and sheer excellent engineering put into the compilers (and in LuaJIT's case, also the interpreter), but PyPy's performance should be a lot better than CPython's for these benchmarks.
I also imagine (though am mostly speculating) that a benchmark involving a full-stack frontend framework like Angular or Ember, with hundreds or thousands of JS objects and lots of DOM manipulation, should put V8's performance a bit closer to CPython's.
I don't think more code will be a big problem for javascript. It seems to mostly affect start up time. Look at the asm.js tests with Massive. Also think about all js projects that use anywhere from 10 000 lince of code (LOC) to 100 000 LOC. I haven't heard anyone saying that the runtime got into any problem. There is always some problems with organizing that amount of code but that is true in almost any language. And javascript is actually quite effective to write in meaning a js program is probably much shorter than the same program in Java (at least before Java 8).
Well, it would be a different comparison; and I dare say a website showing such a comparison would attract a lot of traffic, if only someone would "please take the program source code and the measurement scripts and publish those measurements."
> I also imagine (though am mostly speculating) that a benchmark involving a full-stack frontend framework like Angular or Ember, with hundreds or thousands of JS objects and lots of DOM manipulation, should put V8's performance a bit closer to CPython
Interesting idea! How would we make a version of the benchmark for CPython though?
You couldn't do the DOM parts, but you could compare Python dicts with Javascript objects, and compare performance when there are a lot of heap allocations and GC calls.
A somewhat more fair comparison would be V8 vs. PyPy, Rubinius/RuJIT, HHVM, and LuaJIT. LuaJIT and V8 would likely still come out on top due to the amount of work and sheer excellent engineering put into the compilers (and in LuaJIT's case, also the interpreter), but PyPy's performance should be a lot better than CPython's for these benchmarks.
I also imagine (though am mostly speculating) that a benchmark involving a full-stack frontend framework like Angular or Ember, with hundreds or thousands of JS objects and lots of DOM manipulation, should put V8's performance a bit closer to CPython's.