That kind of question can actually be useful as a proxy for experience with the language, and whether you're the type of person who digs into understanding your tools. If you say "I'm a rockstar Javascript dev", it's very hard to prove it; but if you've never been bitten by some of Javascript's type conversions, and/or have never really looked into some of its intricacies on your own, you probably aren't. It's just one data point, it won't be enough on its own to sway the interview either way, but it's interesting.

To give you an idea, I once interviewed a Javascript dev who said you should null out your variables with 'undefined' when you were finished with them. Oh, why is that? 'Because sometimes they leak out into the global scope and that can cause problems elsewhere in the code.' This person had noted that you could declare a global anywhere in Javascript, but had not noticed, nor asked anyone, nor looked up, nor anything, to find out that there's a difference between "x = 5" and "var x = 5". We didn't hire him.

Had he simply been unaware you -could- declare globals (and had instead said that "x = 5" won't work, you have to use the 'var' key word, or something), we wouldn't have counted it against him; he's following a best practice and never encountered it, fair enough. If he had never been bitten by the scoping rules, fair enough, a minor ding but we'd continue the interview. But the fact he had seen it, possibly been bitten by it, and just handwaved it away as non-deterministic weirdness that required a mystical incantation to avoid? No.