I'm a software engineer, not a meteorologist, but I echo the above comment -- try to learn Python instead if possible. Super useful language in the real world. Matlab is a rare breed rarely encountered outside of academia to say the least, at least in software development. Can't speak whether or not meteorologists write Matlab code in the wild, but I kind of doubt it.
But, to answer your question about pre-reqs, I struggled mightily with my Matlab oriented classes in college because I lacked CS fundamentals. Highly recommend you take a semester or two of Intro to CS (some schools crunch this into 1 semester, others take 2). It will probably be lower level and more straight forward than your JS class. You'll learn the basics of loops, conditionals, variables, functions, etc., and this will help with Matlab considerably. You'll also do some object oriented stuff and learn some basic data structures and algorithms, which is great practical knowledge for the real world, aside from Matlab.
Also, looping back to what I mentioned about my prior struggles with Matlab, Matlab oriented courses are often tough not only because of the programming involved, but the applied math as well. Programming courses offered by non CS departments are usually poorly taught and just suck in general, IMO. I say that as a math major-turned-software engineer who cut his programming teeth writing numerical programming software for applied math courses. If I could do it all over again, I would have focused more on taking courses in data structures, algorithms, and Java/Python as far as languages go. Those courses are generally easier and are more valued by employers at the same time, so they're a win/win. That said, I'm a software engineer and not a meteorologist, so take this advice with that in mind....
That said, if you have to take this Matlab course to get your degree, then I guess you just have to suck it up.