JavaScript is faster than Python and it's under much more active development, thanks to significant investment from Google, Facebook, Microsoft, and thousands of other major companies who pay their employees to improve open source JavaScript tools like Node.js.
Python is a great language to learn if you want to do scientific computing. Some companies, like Quora and Instagram, use Python on the back end. But far more of them use Node.js or are in the process of transitioning to it.