Steve Souders: 10% of the problem is server performance, 90% of problem is browser activity after the main html is downloaded. He wrote the book and developed YSlow, so he should know.
JavaScripts are downloaded serially and block other activity. Most JavaScript functions aren’t used at OnLoad. We could split the JS and only load essential functions up front, and load all the rest later. How much might that help? He says 25% to 50%. This quickly gets complex, but he’s got a simple plan that considers three questions:
- Is the script URL on the same host as the main HTML?
- Should the browser indicate it’s busy, or not?
- Does script execution order mater?
And at that point things started to get too interesting to take publishable notes. I clearly need to pay more attention to this guy.
Stats he mentioned without being specific about the source:
- Google: 200ms longer download time cut revenue by 20%
- Yahoo: 100ms of latency costs … big.