Ajax Performance

Google Code performance improvements: the Souders factor

Steve Souders is now at Google, and the Google Code team has taken some of the advice from High Performance Web Sites and applied it to reduce user-perceived latency. There is no magic in their performance improvements — the techniques (JS/CSS concatenation, CSS sprites, and lazy loading) have been discussed here and elsewhere in the past — but the user-centricity of the approach is what I find most cheering.

The explosion of web performance optimization tools and techniques would be meaningless if we were not focused on improving user experience, and the Google Code team clearly understands this message. The last approach they discuss, lazy loading, is a nice illustration. Rather than initializing the Google loader module in the traditional blocking manner (<script src="blah.js"><script>), the team used the non-blocking DOM scripting approach (document.createElement('script'), set src, append to head). A callback on complete of this operation loads the required APIs.

This approach prioritizes the load time of critical user-visible page elements. To understand the effectiveness of this optimization, you need to measure the time at which the user would perceive the page to be loaded as total page download time may overstate the actual latency. Using experience-centric measurements, the Google Code team saw improvements between 30% and 70% depending on page.