How 2.0 Changed
Here are some highlights of the changes that jQuery 2.0 brings:
No more support for IE 6/7/8: Remember that this can also affect IE9 and even IE10 if they are used in their “Compatibility View” modes that emulate older versions. To prevent these newer IE versions from slipping back into prehistoric modes, we suggest you always use an X-UA-Compatible tag or HTTP header. If you can use the HTTP header it is slightly better for performance because it avoids a potential browser parser restart.
Reduced size: The final 2.0.0 file is 12 percent smaller than the 1.9.1 file, thanks to the elimination of patches that were only needed for IE 6, 7, and 8. We had hoped to remove even more code and increase performance, but older Android/WebKit 2.x browsers are now the weakest link. We’re carefully watching Android 2.x market share to determine when we can cross it off the support list, and don’t expect it to take very long.
Custom builds for even smaller files: This feature has been greatly refined and extended since its debut in jQuery 1.8. You can now exclude combinations of 12 different modules to create a custom version that is even smaller. A new minimal selector engine, basically a thin wrapper around the browser’s
querySelectorAll API, lets you shrink the build to less than 10KB when minified and gzipped. See the README for instructions on how to create a custom build, and remember that any plugins you use will also need to stick to the subset you select.
jQuery 1.9 API equivalence: jQuery 2.0 is API-compatible with 1.9, which means that all of the changes documented in thejQuery 1.9 Upgrade Guide have been applied to jQuery 2.0 as well. If you haven’t yet upgraded to jQuery 1.9, you may want to try that first. Be sure to use the jQuery Migrate plugin.
The full record of changes can be found in the changelog below, and in the list of commits on GitHub.