[nine_k]

JS engines like V8 are very good at JIT and optimization based on actual profiling. If we talk about pure CPU modeling, I suspect a good JIT will soon enough produce machine code on par with best AOT compilers. (BTW the same should apply to JVM and CLR languages, and maybe even to LuaJIT to some extent.)

[andai]

From my cursory reading of v8 blogs, most of its optimizations revolve around detecting patterns in JS objects and replacing them with C++ classes.

[nine_k]

Exactly. Detecting patterns that are typical for human coders and replacing them with stuff that uses the machine efficiently is what most compilers do, even for low-level languages like C. You write a typical `for` loop, the compiler recognizes it and unrolls it, and / or replaces it with a SIMD-based version with many iterations run per clock.