However, JavaScript compilers can optimize your JavaScript code and generate improved code. The compiled JavaScript files are smaller than your original JavaScript files, reducing download times ...

Sparkplug is a new JavaScript compiler that fills the gap between needing to start executing quickly and optimizing the code for maximum performance.

Emscripten C/C++-to-JavaScript project uses a back-end derived from LLVM for greater speed and a more dedicated compiler.

Apple integrates LLVM compiler to boost WebKit JavaScript performance Since compilers already make fast code, why not take advantage?