Ask HN: How do I reach the next level as a developer?

I've been writing Ruby/Rails code for the last 4.5 years and I've noticed that I'm very weak on the front-end (JS/jQuery/etc). It's a pain point for me as I have a hard time wrapping my head around JS syntax.

Are there any good resources you guys (and gals) might recommend for me to level up my front-end skills so that I'm more of a well-rounded full-stack developer?