For any non trivial deep network, any CPU based training is horrendously slow, even if multithreaded. So, Javascript is doomed at it. Python is not, as it can interact with native binaries which may talk with the GPU.<p>&gt; Something that I do not agree with myself, as a Node.js and back-end JS developer<p>NodeJS mostly works when CPU time is not the limiting factor, that is, powering the Web. Neural network is the polar opposite.