What’s New in jQuery 4.0? Major Changes, Size Cut, and Trusted Types Support

jQuery’s core team recently launched version 4.0, described by lead developer Timmy Willison as the first major release in ten years.

Key Compatibility Changes

The new version ends support for legacy browsers such as Internet Explorer 10, older Edge (pre‑Chromium), older Firefox, and outdated Android and iOS browsers. It also adopts native ECMAScript (ES) modules, aligning the library with modern JavaScript standards.

API Reductions and Size Improvements

Several APIs have been removed not because they are deprecated, but because modern browsers now provide native equivalents. This streamlining reduces the gzipped size of jQuery by more than 3 KB. A “slim” build that omits Ajax and animation modules is even smaller, weighing in at roughly 8 KB.

Event‑Handling Adjustments

Historically, browsers differed in the order of focus‑related events (focus, focusin, focusout, blur). jQuery previously normalized these discrepancies. With the W3C specification now widely implemented, browsers follow a consistent event order, and jQuery now defers to native behavior, which may affect code that relied on its overrides.

Trusted Types Integration

jQuery 4.0 adds support for Trusted Types, a browser security feature that mitigates cross‑site scripting (XSS) by preventing unsafe assignments to properties like .innerHTML. Earlier jQuery versions could violate Content‑Security‑Policy (CSP) rules, but the new release resolves this issue.

Historical Context and Adoption

Created by John Resig two decades ago, jQuery solved pervasive browser‑compatibility headaches, allowing developers to use concise selectors such as $("#myspan") instead of document.getElementById("myspan"). According to w3techs, about 88 % of sites using JavaScript libraries (≈70.9 % of all websites) still include jQuery.

Community Opinions

Some developers argue that native JavaScript now offers comparable performance and that the library’s relevance is waning, especially since 19 % of sites still run a ten‑year‑old version. Others contend that jQuery remains the most reasonable JavaScript library for many projects, citing its concise syntax and ease of use.

Conclusion

jQuery 4.0 modernizes the library, reduces its footprint, and improves security, but the decision to adopt it depends on project requirements, browser support targets, and whether developers prefer native APIs over a familiar abstraction.