Julien Lecomte, author of the YUI Compressor gave a talk on High Performance Ajax Applications. He refers to some of the tricks we learnt from Steve Souders' research on the 14 rules for faster-loading web sites but also gives us more insight specifically on fine tuning JavaScript to perform up a gear. I hope you learn a few neat tricks from this video, I know I did.

[source: YUIBlog]

Steve Souders, chief of Yahoo's Exceptional Performance Team, devised 14 rules for faster pages to squeeze more zest from page performance, the rules in short are:

1. Make Fewer HTTP Requests
2. Use a Content Delivery Network (CDN)
3. Add an Expires Header
4. Gzip Components
5. Put Stylesheets at the Top
6. Put Scripts at the Bottom
7. Avoid CSS Expressions
8. Make JavaScript and CSS External
9. Reduce DNS Lookups
10. Minify JavaScript
11. Avoid Redirects
12. Remove Duplicate Scripts
13. Configure ETags
14. Make Ajax Cacheable

After sourcing through numerous high traffic sites they discovered that on average only 12% of a page request is used up by back-end processes whereas the remaining 88% is used up by front-end processes, such as JavaScript, CSS, Ajax and parsing the DOM. This is an interesting analysis but not at all surprising.

Yahoo have also released a handy Firefox plug-in called YSlow which parses a web page and gives you performance analysis based on these 14 rules.