This is true in some situations, but I think is mostly a just-so story told about JITed languages. Here's the problems: 1) Often, you have lots of code that o

This is true in some situations, but I think is mostly a just-so story told about JITed languages. Here's the problems: 1) Often, you have lots of code that only runs once (e.g. UI initialization), or runs rarely (click handlers). By the time the JIT has had an opportunity to observe this code and optimize it, it may be too late. 2) The dynamic nature of JS means that making your code JIT-friendly requires deep knowledge of what language features to avoid. 3) Performance isn't only driven by having the tightest possible machine code. Memory layout is often more important on modern processors. Indirection causes cache misses, and JS objects contain far more indirection than equivalent structs defined in C/C++/Rust. Further, in Javascript you can't really create cache-friendly collections of objects like vectors, BTreeMaps, etc.