Today JavaScript is the second largest contributor to the page load size (after images, source: http://httparchive.org). But while images only affect first impressions, JavaScript can make your app slow for as long as the user interacts with it. It’s therefore critical to understand and tame JavaScript performance.

This session looks at both page delivery and user interaction to highlight patterns and areas of improvement starting with proper benchmarking and profiling. Understanding what to improve (e.g. DOM manipulation) is as valuable as understanding what not to bother with (e.g. unrolling loops) We’ll also look at some of the new and shiny in HTML5 and ECMAScript5 and how certain features affect performance, e.g. data-* attributes, localStorage and various "shims".