Ask HN: Libraries for cross-platform client-side machine learning?

I've been building out a side-project product of mine that is initially going to be a web app, but probably will include native/hybrid iOS and Android apps in the future. The product involves a component with machine learning (specifically NLP classification). The obvious solution is to build my server in Python and run the processing with NLTK, but ideally the product would work even without internet, so I'm wondering if any solutions exist to offload the processing to all 3 major client-side platforms.

Right now the two solutions I can think of are: use a JS librasry (the ecosystem seems fairly immature), or use a C++ library for iOS and Android and compile into JS with emscripten (but then I have to deal with C++). Any thoughts?