In the past few years, performance research has become more prevalent thanks to research by the Yahoo! Exceptional Performance Team and Google’s Steve Souders. Most of that research studies not the individual HTML page, but the resources the page requires to display or behave correctly.
Although both CSS and JavaScript may be included within an HTML page, best practices encourage storing CSS and JavaScript in external files that can be downloaded and cached separately. Performance research asks: How can these external resources be downloaded and applied most efficiently? The first approach is to limit the number of external requests since the overhead of each HTTP request is high. The second approach? Make your code as small as possible.
