Well, depends how you define "master". To become a leading expert on it would mean taking time away from other skills, which probably wouldn't be wise. But if you're using JS quite a lot then learning it to an arbitrary level, let's say 80% of "master", well, that probably would be a good shout.
I suppose it depends on your skillset projection, do you see yourself spending a lot of the next five years with JS? If so, invest now in personal development. If not, maybe skim read it.
If you're going to make JS your primary language that you write on a daily basis, doesn't it make sense to invest more time into learning it than just whatever you might accidentally pick up through trial-and-error?
Most developers in most other languages do tend to take formal learning of the language, to a deep extent often, a more serious task, but with JS it seems many developers just kinda get whatever they get along the way.
I have found that approach to be good at getting and keeping yourself employed, but bad at giving you any confidence that you actually know what's going on. If you aren't really sure exactly why your code works, my theory is that you'll never know exactly why your code doesn't work either.
I'm just trying to provide resources for developers who want to take learning JS seriously, and challenge "all" of us to ask, "just how much DO I know JS?" The rest is up to you. :)