Hotspot among with other JVMs are no doubt fast -- but partially that came from Java being a static and compiled language.

Not saying that JavaScript is faster, but JavaScript is fast. If you look at the benchmarks I posted, you'll notice that 50% slower is hardly the norm -- many benchmarks have the VMs performing at a near-native performance, and the VMs are even faster in some cases.

In fact, number crunching in JavaScript has been fast for a long time, and even faster than Java in some cases: http://www.stefankrause.net/wp/?p=144

I'm not trying to advocate JavaScript's performance in anyway however. I'm merely pointing out the fact that performance cannot be single-handedly described as "fast" or "slow", especially "for sure". Context matters. A lot.

> still 50% slower theoretically than native code

How can something be theoretically slower? What's the difference between theoretically slower and practically slower?

Only practical implementations have a speed that you can talk about.

I don't know what you mean by 'theoretically' as an adverb there.

I suspect it means something like "according to calculations using a noticeably approximate model of reality". That's what people tend to mean, anyway. "Theoretically" is often code for "My model does not correspond to reality".

It annoys me, actually, that "theory" has this negative connotation of noncorrespondance.