[randommodnar]

Actually JavaScript is compiled JIT by most engines these days. While it's not the fastest, it certainly can be quite fast.

[robenkleene]

I see, good point, but then I'd expect the cost of JIT compilation would still have a performance cost? As opposed to Objective-C being compiled before distribution to the client?

[pcwalton]

JIT compilation cost is minimal in practice due to tiered JITs.