Performance is a hugely important area of web development. If your site runs slowly, users are going to leave, and the problem only grows as your site gets more popular. Pro JavaScript Performance gives you the tools you need to keep your sites smooth and responsive no matter how many users you have. Best practices are changing or becoming redefined continually because of changes and optimizations at the interpreter level, and differences in system configuration, and network speeds.  This is exacerbated by the quickened release schedule that most browsers have adopted. Just as important as following best practices is the ability to measure your own performance, so that you can adjust as times change, and so that you can note the subtle nuances in your own code and define your own best practices by your own observations.
This book gives you the tools to observe and track the performance of your web applications over time from multiple perspectives, so that you are always aware of, and can fix, all aspects of your performance.