This is the second talk that follows-up on the 14 best practices from YSlow and “High Performance Web Sites”. The first talk presented three new best practices: Split the Initial Payload, Load Scripts Without Blocking, and Don’t Scatter Inline Scripts.
The most important of these is loading external scripts without blocking other downloads and preventing page rendering. One complication is this may introduce undefined symbol errors if inlined code uses symbols from the external scripts. Luckily, there are several techniques to workaround this problem. That and other topics will be covered in this presentation of three more best practices:
* Coupling Asynchronous Scripts
* Use Iframes Sparingly
* Flush the Document Early
Much of this talk discusses material from Steve’s book, High Performance Websites: Essential Knowledge for Front-End Engineers. The talk is full of great advice, I found the discussion around loading scripts both synchronously and asynchronously and the performance gains that can be achieved. However this has to be combing with understanding that you also have to couple scripts together in order to preserver the order they are loaded in, as well as understanding that by default loading external scripts blocks download of other elements on the page. Steve discusses a number of techniques that can address these issues as well as the pros and cons associated with each. His discussion around John Resigs idea of using degrading script tags is extremely useful.