JavaScript can be a good language for machine learning in the sense that it allows to concretely use machine learning everywhere and this fact will become increasingly important. It is not the language with the bigger support from the community in terms of machine learning but it is the language with the highest chance to be used in ubiquitous machine learning development as soon as AI becomes mainstream all around the world. Not because of quality considerations but just because of the fact that systems have to be distributed to customers, especially through the web, and JavaScript is a choice that makes always more sense.
If you can spend some minutes give a look to DN2A - Digital Neural Networks Architecture. You can find it here: https://github.com/dn2a/dn2a-javascript