Javascript has a compiler called Babel, which plays a huge role in modern web development. It is in fact a transcompiler, meaning it doesn't turn your javascript into bytecode, it is just transpiling stuff without changing the level of abstraction.

React Compiler is just a babel plugin for automatic performance improvement, memoization specifically, for never perfectly memoized React code.

Can library have compiler? Well why can't it? For example stdlib has a compiler, because C does.