jQuery 4.0.0 Support: What’s New and How Kendo UI Has You Covered

Hello, world, from jQuery 4! Take a look at the noteworthy changes and see how to get up to date with the framework and with Kendo UI for jQuery.

After almost a decade, jQuery 4.0.0 has arrived. With this release, jQuery removes legacy browser support, drops deprecated APIs, aligns event behavior with modern standards and modernizes the codebase. If you’re maintaining applications that still use jQuery or libraries built on top of it, this release is worth understanding.

And the best part? Progress Kendo UI for jQuery is fully compatible and ready for jQuery 4.

What’s New in jQuery 4?

Below is a breakdown of what actually changed, why it matters and what you need to update in your own code.

Modernized Core

• ES modules + Rollup packaging for compatibility with modern bundlers and <script type="module"> workflows.
• Leaner build: Removal of legacy browser branches and deprecated APIs (~3 kB gzipped reduction; slimmer “slim” build without Deferred/Callbacks).
• Spec alignment: Focus/blur events follow W3C ordering across modern browsers.
• Internal cleanup: Prototype no longer exposes internal push/sort/splice; “magic” behaviors reduced; toggleClass(boolean) legacy signature removed.

Security and CSP

• Trusted Types support and broader use of <script> transport to avoid CSP violations; fewer inline‑script pitfalls for AJAX/script loading.

Browser Support

• Dropped: IE 10 and older, Edge Legacy and very old Firefox/iOS/Android Browser versions. If you must support these, stay on jQuery 3.x. (Be aware that IE 11 removal is planned for jQuery 5.)

Removed APIs (Upgrade Call‑outs)

The following helpers are gone, switching to native equivalents is recommended:

• jQuery.isArray → Array.isArray
• jQuery.parseJSON → JSON.parse
• jQuery.trim → String.prototype.trim
• jQuery.type
• jQuery.now → Date.now
• jQuery.isNumeric
• jQuery.isFunction
• jQuery.isWindow
• jQuery.camelCase
• jQuery.nodeName
• jQuery.cssNumber
• jQuery.cssProps
• jQuery.fx.interval

Additional behavior changes:

• Prototype internals removed: Push/sort/splice are no longer on jQuery objects. Use native array-call patterns: [].push.call($elements, item);.
• Event order change: Focus/blur now follows the W3C sequence blur → focusout → focus → focusin, so retest any flows that depended on the old order.
• Removed: Autopromotion of JSON→JSONP; toggleClass(boolean|undefined) legacy signature.

Kendo UI Readiness

Kendo UI for jQuery has already validated and fully supports jQuery 4.0.0. We’ve run the full suite of components and integration tests against jQuery 4.0.0 to confirm compatibility across all widgets and core modules.

We removed or updated all deprecated jQuery APIs used inside Kendo UI and aligned event/focus handling with the new spec. Any internal usage of jQuery helpers, removed in 4.0.0, such as $.trim, $.isNumeric or prototype array method shortcuts, has been replaced with native equivalents. We also updated our focus/blur logic to match jQuery’s W3C‑aligned event order to enable consistent behavior across modern browsers.

You can upgrade Kendo UI + jQuery together without code changes in Kendo UI dependencies. All required migration work has been handled in the library itself. If your application uses Kendo UI as intended (through its public APIs), no adjustments are needed.

Any upgrade tasks will only apply to your own direct jQuery usage (outside of the Kendo UI bundle) where removed helpers or legacy patterns might appear.

Practical Guidance for Your Apps

• Replace removed helpers ($.trim, $.isNumeric, $.parseJSON, etc.) with native equivalents.
• Retest focus/blur‑dependent logic (keyboard navigation, composite widgets, validation triggers).
• Review AJAX/JSONP paths if you depended on JSON→JSONP auto‑promotion or specific script transport edge cases.
• Stop using prototype internals (push/sort/splice) on jQuery objects; swap to native array‑call patterns.
• For strict CSP apps: leverage Trusted Types and avoid inline loaders; prefer script‑based transport.
• Consider the slim build if you don’t use Deferred/Callbacks and want the smallest footprint.

Quick Upgrade Checklist

1. Update to jQuery 4.0.0 and the latest version of Kendo UI for jQuery.
2. Scan your code for removed helpers and legacy signatures; replace with native equivalents.
3. Retest focus/blur-dependent flows and any custom AJAX/JSONP logic.
4. For strict CSP apps, verify Trusted Types and script loading paths.

If you’re new to Kendo UI, the library comes with a free 30-day trial.

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