So this is a crossroad right? A lot could be said about this but the truth is the following. On the one hand front end is a beast whose evolution is lightning fast. It is really hard to master all these techniques, concepts, frameworks, new JS syntax and standards, web components and it goes on and on.
On the other hand it is extremely important if you can understand fast and accurately what the rest of the team needs from you. I mean do you know what a RESTful API is or what are the most important HTTP response status codes apart from 404 or 500? What it is CORS or maybe how you can update your views using sockets and asynchronous events? All these demand the cooperation of the 2 worlds, backend and front end. That kind of knowledge doesn't make you a full stack developer but it does make you a better / stronger team member and more efficient front end developer of course. Great projects depend on great teams, that's certain.
I 've met some great developers and i could barely cooperate with them because of their arrogance and their stupidity. You know sth like i have some years experience with RoR or Django so you should find a way to work with whatever i am sending with the API endpoints i create. No this attitude is awful. We are engineers, smarter by far to end up like this right?
To be honest i am extremely confident in doing front end job because of my experience with backend etc. I have created so many APIs so now i know exactly what my views need or how we could make sth better / faster etc. This knowledge is so important for my team's decisions and cooperation. It really helps a lot.
What i recommend then? Study hard JS since you want to make a living out of it but you should definitely get your hands dirty with backend coding to understand even better how some things work. Create a small Blog or a Portfolio and force yourself to write down a small API. There are so many great tools out there for every language like RoR, Django and Laravel. Just go for it!!