Ask HN: Resources for catching up on modern JavaScript for Python/C++ Programmer

When first learning to program (back in high school 10+ years ago) I played around a lot with JavaScript, building 'cool' websites that did all kinds of things in JavaScript. I haven't really touched it since. I moved on to Java and now program professionally in Python and C++ (desktop apps development) and do some webapps development as side projects. I've found myself doing lots of data visualisation and analysis (performance benchmarking etc) and for the most part I used Matlab and various python libraries to achieve this - but I've been lately using the great Charts.js library. I would love to get up to speed with how 'modern' JS works for frontend development. I'm not so concerned with learning particular frameworks in depth (but should I be?) - moreover what particular programming/design paradigms are considered the most effective? What resources have people in a similar situation to me found to be useful?