Nope. My frontend knowledge has disappeared in the last year as I've done almost all backend. My knowledge of JS is enough to get the job done but deep knowledge? How could it be - I'm constantly building products, not toying with the minute of performance optimization or creating some impressively large framework. The stuff I do is extremely lean and relies very little on language nuances. The stuff I do could be done easily in many languages - it just happened to be in JS a lot of the time.