This book compares badly with the O'Reilly "JavaScript, The Definitive Guide". There is a very limited amount of discursive material and that material is fairly poorly organised and lacking in xcross-reference information. This book does not give one an understanding of how the language works. Other reviewers might retort that this is not a tutorial book, but other works prove that it is quite possible to write a reference work which also describes the language usefully for an experienced programmer. I took the book back and replaced it with O'Reilly.