What’s New in jQuery 4.0.0 Beta? Major API Removals and Browser Support Changes

jQuery is a fast, concise JavaScript framework created by John Resig in 2006 with the motto write Less, Do More, providing a simple design pattern for DOM manipulation, event handling, animation, and Ajax.

4.0.0 Beta!

After a long development cycle, jQuery 4.0.0 beta is now available. The release includes bug fixes, performance improvements, and several breaking changes, most notably the removal of support for Internet Explorer <11.

Goodbye IE <11

Support for IE 10 and earlier has been dropped, and IE 11 support will be phased out in jQuery 5.0, shaving roughly 867 gzip bytes from the library. Legacy browsers such as Edge Legacy, iOS <11, Firefox <65, and the Android browser are also no longer supported; developers needing those browsers should stay on jQuery 3.x.

Removed Deprecated APIs

The following functions, long‑standing deprecations, have been removed because native equivalents now exist in all supported browsers:

jQuery.cssNumber

jQuery.cssProps

jQuery.isArray

jQuery.parseJSON

jQuery.nodeName

jQuery.isFunction

jQuery.isWindow

jQuery.camelCase

jQuery.type

jQuery.now

jQuery.isNumeric

jQuery.trim

jQuery.fx.interval

Removed push , sort and splice from the jQuery prototype

Historically jQuery’s prototype exposed Array methods that behaved differently from native methods and were intended for internal use only. These have been replaced with native Array calls. For example, $elems.push(elem) is now implemented as [].push.call($elems, elem). Plugins that relied on the old prototype methods may need adjustments.

Unified focusin and focusout event order

All browsers supported by jQuery 4.0 now follow a consistent event ordering for focusin, focusout, focus, and blur. This differs from the order jQuery chose years ago, but it aligns everyone on the same page.

FormData support

jQuery.ajax

now automatically handles binary data, including FormData. Previously binary data were treated as unknown and stringified; developers could disable conversion manually. The new behavior matches expected native handling.

Automatic JSONP upgrade removed

Earlier versions automatically converted jQuery.ajax calls with a callback and dataType:"json" into JSONP requests. jQuery 4.0 relies on CORS for cross‑origin requests, eliminating the hidden JSONP conversion and reducing unexpected behavior.

jQuery source migrated to ES modules

The main branch’s source code has moved from AMD to native ES modules, enabling direct imports without a build tool. The project now uses Rollup for bundling, and all tests run against the ES‑module build.

A comprehensive upgrade guide and the jQuery Migrate plugin will be provided before the final release to help developers transition.