jQuery 4.0: Modernization After a Decade Signals Evolution Over Obsolescence

Nearly a decade after jQuery 3.0's release, the foundational JavaScript library has launched jQuery 4.0, coinciding with its 20th anniversary. This release strategically modernizes the library while preserving the developer experience that made it ubiquitous. The update reflects a deliberate evolution rather than reinvention, focusing on removing historical baggage while acknowledging contemporary web standards.

Core Modernizations

Key architectural shifts drive this release:

• Browser Support Culling: Internet Explorer 10 and older, Edge Legacy, and obsolete mobile browsers are officially deprecated. IE11 remains temporarily supported but is earmarked for removal in jQuery 5.0.
• ES Module Adoption: The codebase migrated from AMD to native ES modules (GitHub source), enabling import syntax and seamless integration with modern bundlers like Rollup.
• API Pruning: Deprecated methods including jQuery.isArray, jQuery.parseJSON, and jQuery.trim were removed where native browser APIs now suffice (e.g., Array.isArray()). This reduced the gzipped core by over 3KB.
• Security Alignment: Added Trusted Types support prevents CSP violations when manipulating HTML, shifting script loading to <script> tags instead of inline scripts.
• Slim Build Optimization: Removal of Callbacks/Deferreds (superseded by native Promises) shrinks the slim build to ~19.5KB gzipped.

Community Reception and Relevance

Despite debates about jQuery's role in modern web development, the update sparked notable discussion. A Reddit thread with 130+ comments revealed nuanced perspectives:

"Why use this on any greenfield app?"

"Maintaining large legacy codebases, cross-browser normalization, and enabling lightweight interactivity without framework overhead. It's boring, and boring can be good."

Hacker News users acknowledged that jQuery's syntax remains "shorter and cleaner than vanilla JS" for DOM manipulation. The library's stability contrasts sharply with churn in modern frameworks—a virtue for applications prioritizing longevity over trend adoption.

Strategic Trade-offs

jQuery 4.0 exemplifies intentional technical debt reduction. By shedding legacy APIs and browsers, the team achieved:

• Performance Gains: Smaller payloads and optimized internals
• Security Hardening: Alignment with modern CSP requirements
• Toolchain Compatibility: ES modules work with contemporary build systems

The trade-off is explicit: projects requiring IE10 support or using removed APIs must either delay upgrading or use the jQuery Migrate plugin. This positions jQuery as a pragmatic choice for:

1. Legacy application maintenance
2. Progressive enhancement of server-rendered sites
3. Cross-browser normalization in constrained environments
4. Rapid prototyping without framework toolchains

The Path Forward

Available via npm and the jQuery CDN, version 4.0 demonstrates how foundational tools evolve. Unlike frameworks that compete for mindshare, jQuery's strategy focuses on incremental adaptation—proving that even "completed" projects benefit from calculated modernization. As one Reddit user noted, its millions of daily downloads signal enduring value beyond nostalgia.

Daniel Curtis is UI Development Manager at Griffiths Waite, specializing in TypeScript and modern web architecture.