Another javascript book, where the author has shown they're not up to the job, I do not own the book, having only perused it, but I've seen lots of people who have read the book and come away deeply confused about how to author scripts due to the authors insistence on "Browser Detection" based on the User or Distributor definable UserAgent strings. This is completely unsafe and should never be used. Please choose another javascript book to learn client-side javascript programming.