BTW, I don't know if that's true. I'm not aware of the sales figures of any other Ruby books, but O'Reilly's The Ruby Programming Language has consistently had a sales rank (on Amazon) higher than my book. So has Pragmatic Bookshelf's Programming Ruby.
You outsold Resig, which is probably the best-known JS book. I'm not saying you're the most successful book ever, but you're in a hot area and you're in the top quartile of titles.
I'd argue that David Flanagan's excellent The Definitive Guide To JavaScript is better known than Resig's book.
In addition, "beginner" books tend to sell better than advanced books aimed at professionals, which might explain the relatively low sales of Resig's book.
BTW, I don't know if that's true. I'm not aware of the sales figures of any other Ruby books, but O'Reilly's The Ruby Programming Language has consistently had a sales rank (on Amazon) higher than my book. So has Pragmatic Bookshelf's Programming Ruby.