V8 (and other Javascript JIT compilers) are written in C++. Whenever you think you run Javascript code, what you are actually running is C++ code that will emulate and compile your Javascript into machine code, update the DOM with C++ code, access sockets using C/C++ code etc. all running on an OS written in C/C++. Your code is a very small percentage of the code that runs "your" application. C/C++ runs the world. Including Javascript, Python, Java etc.