This poor site is now experiencing the HN hug of death...
If it's C++, then emscripten might be a possible choice.
If it's a mixture, then that's a much harder problem...
https://github.com/cryos/avogadro/
Mostly C++, then the clojure wrappers in java? There do exist pure javascript molecule drawers, though.
Does making a chemical drawing usually take that much time?