Essential performance best practices for jQuery

It depends on the selector and the browser. Something like $(".myclass") is worth caching on IE7 because it requires a pass through the entire document; there's no `querySelectorAll` or `getElementsByClassName`.

I wouldn't start by caching selectors all over the place unless you profile and see that it's slow. Doing a lot of selecting in a `scroll` or `mousemove` handler would be a bad idea though: http://ejohn.org/blog/learning-from-twitter/

I think the point there was that if you have a lot of setup to do, try to defer as much as possible past `.ready()` so that the user will have something to look at.

However, if you wait until the `load` event happens, the page is visible and the user can start interacting with it. If you're still messing with the HTML at that point it can be pretty confusing for the user. That's really common with pages that decide for example to AJAX back for saved settings; they can yank the defaults out from under you while you're typing! The southwest.com site does that and it drives me crazy.

None of the recommendations should be seen as absolutes, and some conflict with each other. For example, if you're using event delegation you've got to be careful in caching selectors to content that may go away.

Just don't forget that you can use .delegate() now, instead of the solution offered in the article (which is more than two years old).

Yeah, the article is from April 2009. I realized that when he mentioned jQuery 1.3.