Most Lisp libraries won't automatically work with Parenscript -- think of Parenscript as just being more Lisp-like syntax for JS, rather than a compile from Lisp to JS. It's quite useful if you want to dynamically generate JS, or wish JS had macros, but it won't give you trivia for free.

Hopefully some day there'll be a production-quality Lisp implementation that runs in WebAssembly... Though, I wonder if you could hack together ECL and emscripten?