The main difference between #4 and all other cases is that the first time when you use a closure as a constructor is always quite expensive. It is always handled in V8 runtime (not in generated code) and transition between compiled JS code and C++ runtime is quite expensive. Subsequent allocations usually are handled in … Read more
There are various approaches to JavaScript execution, even when doing JIT. V8 and Nitro (formerly known as SquirrelFish Extreme) choose to do a whole-method JIT, meaning that they compile all JavaScript code down to native instructions when they encounter script, and then simply execute that as if it was compiled C code. SpiderMonkey uses a … Read more
These are the details that I’ve been able to dig up. It’s worth noting first that although JavaScript is usually considered to be interpreted and run on a VM, this isn’t really the case with the modern interpreters, which tend to compile the source directly into machine code (with the exception of IE). Chrome : … Read more