Probably the most complete and updated book that you may find about Javascript.The author made a great job writting about some of the most important topics on javascript development and highlighting the difference among browsers.Most of the topics are already covered in other javascript books I have read before, but not in the way Nicholas does, he usually goes deeper on every topic.If you have some knowledge on javascript and want to reach another level, this is the book for you. If you consider yourself a guru, you may enjoy it as well, but definitely, not for newbies.