jQuery 1.9 removes or modifies several APIs that behaved inconsistently or inefficiently in the past. The majority of these changes have been foreshadowed by their deprecation in previous versions of jQuery, particularly 1.7 and 1.8.
In making these changes, the team's goal was to fix behavior that makes jQuery inconsistent or hard to use, and in the process improve both file size and overall performance.
This list is deceptively foreboding. Most of these changes address special situations and edge cases, and a few are changes that have been widely requested where jQuery's historical behavior has been problematic. As a first step, the best way to see if your code works is to try it with both jQuery 1.9 and the Migrate Plugin as described below.
For now, this guide serves as an appendix to the standard jQuery API documentation, and those pages may not describe the behavior of version 1.9. Please be patient while we update the documentation for the individual pages at api.jquery.com to reflect the changes in 1.9.