The release candidate of JQuery 3.0 has been released, with changes to clean up the API, and fixes for bugs that may prove to be breaking changes for some code.

The cleaning up process involves the removal of previously deprecated public APIs, changes to or removal of undocumented APIs, and changes to the documented or undocumented behavior of existing APIs for specific inputs.

The JQuery JavaScript library is installed on the majority of the sites on the web with high traffic. It was designed to make it easier to script client-side HTML, and is the most popular JavaScript library. When released, jQuery 3.0 will become the only version of jQuery. The 1.12 and 2.2 branches will still be supported with critical support patches, but there will be no new features or major revisions for them.

The majority of the work for this release has been to clean up the APIs, and there are correspondigly fewer feature improvements. The developers say that although the changes warrant the version number change, they anticipate that these releases shouldn’t be too much trouble when it comes to upgrading existing code, adding:

"Yes, there are a few “breaking changes” that justified the major version bump, but we’re hopeful the breakage doesn’t actually affect that many people."

There's also a jQuery Migrate 3.0-rc plugin to help identify compatibility issues in your code.

Among the new features, jQuery.Deferred objects have been updated for compatibility with Promises/A+ and ES2015 Promises. This involved making some major changes to the .then() method, so an exception thrown in a .then() callback becomes a rejection value, and callbacks are always invoked asynchronously. 

Another change means that error cases don’t silently fail. The developers explain that this is an attempt to avoid the situation where you accidentally make a crazy request, and don't know why nothing happened. jQuery 3.0 will instead throw errors so you can tell why your request failed.

Animations have been improved on platforms that support the requestAnimationFrame API, (essentially everything bar old Androids pre 4.4, and IE9) If your platform supports that API, jQuery will now use it, giving you smoother animations that use less CPU time. The developers attempted using this API some time ago but withdrew the facility because of compatibility issues with existing code. These problems have been overcome, and the support is back.

More Information

Upgrade Guide

jQuery Migrate 3.0-rc plugin

Release Candidate

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