Hm... I think the biggest issues I experience have more to do with frontend design rather than composing JS itself.
I love using it as a "one-off" scripting language which usually involves interaction with some sort of an existing codebase.
I'm also fairly confident in doing any sort of backend-centric work, in which existing components most likely exist as well (or at the very least something POC-esque to iterate on or scaffold from).
With that said I believe most of these difficulties stem from most of my experience being backend-centric roles, so when it comes time to implement a frontend from scratch, I become unsure of where to start. The sheer amount of technologies available and vast amount of flexibility is also very intimidating.
However I've been slowly but surely immersing myself in the stack(s), and have found that much like my experience with CSS the best way to learn is to simply do it-- making mistakes and learning from them in my exploratory learning.
I do appreciate what you said about build pipelines and feel much better about my current projects :-)
quick edit: I think my lack of experience in functional programming is another factor here, however Typescript's object orientated style is very attractive.