I'd note that I've seen cases where the V8 JIT was sufficiently good that thunking to C++ and back meant that the performance difference was minimal. But that

I'd note that I've seen cases where the V8 JIT was sufficiently good that thunking to C++ and back meant that the performance difference was minimal. But that was for 'js library backed by C++' shaped cases whereas for performance critical app-specific code you probably want 'C++ library that presents a JS interface at the top level.'