Reply to Message

As far as I'm concerned, somebody who calls himself a javascript developer should understand the concept of inheritance and thus the concept of prototyping. It's really not that hard to get, it's just not the same as in other (mainstream) languages. But once you get it, it's very useful and you'll be wondering how you ever managed without.
I'm not trying to brag here, it's really not that difficult, just pick up a book about JavaScript or read the link in the article twice and you're good to go (which is the least you can do to prepare for an interview).