I'm a web components guy myself, but that's not the equivalent JavaScript functionality at all, as XSLT doesn't event have components.

XSLT is a functional transform language. The equivalent JavaScript would be something like registry of pure functions of Node -> Node and associated selectors and a TreeWalker that walks the XML document, invokes matching functions, and emits the result into a new document.

Or you could consume the XML as data into a set of React functions.