jQuery 4.0.0 BETA! | Official jQuery Blog

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Posted on by Timmy Willison

jQuery 4.0.0 has been in the works for a long time, but it is now ready for a beta release! There’s a lot to cover, and the team is excited to see it released. We’ve got bug fixes, performance improvements, and some breaking changes. We removed support for IE<11 after all! Still, we expect disruption to be minimal.

Many of the breaking changes are ones the team has wanted to make for years, but couldn’t in a patch or minor release. We’ve trimmed legacy code, removed some previously-deprecated APIs, removed some internal-only parameters to public functions that were never documented, and dropped support for some “magic” behaviors that were overly complicated.

We will publish a comprehensive upgrade guide before final release, to outline the removed code and how to migrate. The jQuery Migrate plugin will also be ready to assist. For now, please try out the beta release and let us know if you encounter any issues.

As usual, the release is available on our CDN and the npm package manager. Third party CDNs will not be hosting this beta release, but will host the 4.0.0 final release later. Here are some highlights for jQuery 4.0.0 beta.

Table of Contents

Goodbye IE<11

jQuery 4.0 drops support for IE 10 and older. Some may be asking why we didn’t remove support for IE 11. We plan to remove support in stages, and the next step will be released in jQuery 5.0. For now, we’ll start by removing code specifically supporting IE versions older than 11, giving us a size reduction of 867 gzipped bytes in one PR!

We also dropped support for other very old browsers, including Edge Legacy, iOS <11, Firefox <65, and Android Browser. No changes should be required on your end. If you need to support any of these browsers, simply stick with jQuery 3.x.

Deprecated APIs removed

These functions have been deprecated for several versions. It’s time to remove them now that we’ve reached a major release. These functions were either always meant to be internal or ones that now have native equivalents in all supported browsers. The removed functions are:

push, sort, and splice removed

The jQuery prototype has long had Array methods that did not behave like any other jQuery methods and were always meant for internal-use only. These methods are push, sort, and splice. We switched our uses of these methods to Array functions instead of the jQuery prototype. For example, $elems.push( elem ) became [].push.call( $elems, elem ). We’re mentioning it here in case there are any plugins out there that may have relied on these methods.

focusin and focosout event order

For a long time, browsers did not agree on the order of focus and blur events, which includes focusin, focusout, focus, and blur. Finally, the latest versions of all browsers that jQuery 4.0 supports have converged on a common event order. Unfortunately, it differs from the consistent order that jQuery had chosen years ago, which makes this a breaking change. At least everyone is the on the same page now!

jQuery’s order for all four events in previous versions was:

1. focusout
2. blur
3. focusin
4. focus

Starting with jQuery 4.0, we no longer override native behavior. This means that all browsers except IE will follow the current W3C specification, which is:

1. blur
2. focusout
3. focus
4. focusin

For those that are curious, the W3C specification previously defined a different order:

1. focusout
2. focusin
3. blur
4. focus

But, few thought that intuitive and the spec was changed in 2023 to match what browsers have already implemented. Ironically, the only browser to ever follow the old spec was Internet Explorer.

FormData support

jQuery.ajax has added support for binary data, including FormData. Previously, binary data was not a known data type and was converted to a string. That behavior could be disabled by disabling data conversion and handling the data manually, but we decided to make this work automatically. This is technically a breaking change, but should be closer to expected behavior.

Automatic JSONP promotion removed

Previously, jQuery.ajax with dataType: "json" with a provided callback would be converted to a JSONP request. Today, the preferred way to interact with a cross-domain backend is with CORS, which works in all browsers that jQuery 4.0 supports. This should help avoid unexpected behavior in case a developer is unaware that code can be executed from a remote domain with JSONP.

jQuery source migrated to ES modules

It was a special day when the jQuery source on the main branch was migrated from AMD to ES modules. The jQuery source has always been published with jQuery releases on npm and GitHub, but could not be imported directly as modules without RequireJS, which was jQuery’s build tool of choice. We have since switched to Rollup for packaging jQuery and we do run all tests on the ES modules separately.

Trusted Types and CSP

jQuery 4.0 adds support for Trusted Types, ensuring that HTML wrapped in TrustedHTML can be used as input to jQuery manipulation methods in a way that doesn’t violate the require-trusted-types-for Content Security Policy directive.

Along with this, while some AJAX requests were already using to avoid any CSP errors caused by using inline scripts. There are still a few cases where XHR is used for asynchronous script requests, such as when the "headers" option is passed (use scriptAttrs instead!), but we now use a


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