The book also includes dubious language-agnostic techniques like Duff's device and backward counting loops. Without guides to profiling, performance tuning principles, and an understanding of JS implementations, all of which the book lacks, this kind of advice will cause more harm than good in the hands of novice JS programmers, and its inclusion into an introductory book on JS performance tuning is questionable. The same can be said for the IE6-specific performance hacks mentioned throughout the book.
While the book has good coverage of contemporary JS profiling tools, it does not attempt to teach approaches to profiling and identifying bottlenecks. Also missing are tips on isolating sources of DOM access and reflow penalties.