JQuery 1.4 appeared almost a year after it’s predecessor -  jQuery 1.3.2. Reason enough to assume some new features have been extensively developed in this version. Let’s have  a look at a few of the newly introduced functionalities that struck me as particularly useful:

The focus has been both on the reduction of internal complexity in the jQuery codebase and improving the development processes behind it with regards to code consistency, testing and optimization.

The cleanup of jQuery internals has made it possible to apply certain new and excisting functionalities more consistently throughout the jQuery 1.4 codebase, and bring major improvements in performance.
The full release notes for the 1.4 version can be read here:
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