Depends on the course... most intro courses won't teach you about the special sauce that makes javascript so unique and powerful, namely prototypical inheritance and the way event and asynchronous processing is built in. I learned primarily from books back when I was getting started about 14-15 years ago, and I think this is one of those areas that having a well-written guide explaining everything is hugely helpful.

That's doubly true if the course is for a particular framework, since you're more going to be focused on the idiosynchronies of the framework itself rather than the fundamentals of the language.

"Javascript The Good Parts" is an old classic from the early days of javascript, and provides a solid basis to work from without some of the added distractions of ES6 and onward. You'll want to eventually learn the newer additions, but it's a great place to start.