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.

What do you classify as deep? I feel comfortable with JS and have a vague understanding of the internals of front end frameworks, but I wouldn't consider myself to have deep knowledge of either.

It's relative to your other skills. If you were a novice at everything and intermediate at JS then that's the trunk of your T.