This book assumes a decent knowledge of HTML, which is nice, since some other books feel they need to walk you through HTML as well as JavaScript. However, don't expect too much from this book though it is a good introduction.
One amusing aspect is that Mr. Shelley often finds himself confusing himself in his eforts to explain the way JavaScript works.
In summary, if you want to start learning JavaScript, this is a good start, but it may not answer all your questions, and certainly will not make you a JavaScript master.