The final versions of jQuery 1.9 and jQuery Migrate 1.0 and the beta of jQuery 2.0 have been released. So has the jQuery Plugin Registry, a new website to serve as a central repository.

The key feature of jQuery 1.9 and 2.0 is that they are removing a lot of old code to produce a streamlined API that will result in a cleaner code base for future development work. The biggest impact will be on older versions of Internet Explorer.

While jQuery 1.9 will support IE 6, 7 and 8, jQuery 2.0 will only support IE 9 or later.  Although the two versions share the same API, the jQuery 2.0 beta is ten per cent smaller than the 1.9 release and the development team believes it can shrink it further, stating in the blog post:

There is more refactoring possible now that we can consistently depend on modern JavaScript, CSS, HTML, and DOM features being there.

To cope with problems that might arise from removed functions, jQuery Migrate is a plug-in designed to help with the migration of code to jQuery 1.9 and later. It not only provides warnings when deprecated functionality is in use, but can also restore APIs to allow production code to continue running.

Apart from the streamlined API the main new features in jQuery 1.9 are:

New .css() multi-property getter: Now you can pass .css() an array of CSS property names and it will return an object with the current values of all those CSS properties:
var dims = $("#box").css([ "width",
                 "height", "backgroundColor"]);
// { width: "10px", height: "20px",
              backgroundColor: "#D00DAD" }

Enhanced cross-browser CSS3 support: jQuery 1.9 now supports the following CSS3 selectors across all browsers, all the way back to IE6: nth-last-child, :nth-of-type, :nth-last-of-type, :first-of-type, :last-of-type, :only-of-type, :target, :root, and :lang.

New .finish() method:  to immediately complete all the animations queued on an element. 

Source map support: You can now run the minified version of jQuery but use source maps for debugging. This can be extremely valuable for tracking down problems on a production web site.

To further help developers working with jQuery the new jQuery Plugin Registry is intended to reduce the fragmentation and distribution problems that can be obstacles for plugin developers and consumers. The new website is quickly being populated with plugins and the details of how to upload plugins is also explained in the jQuery blog.