jQuery 4.0.0 Is Here: What It Means for Your Codebase in 2026

On January 17, 2026, the jQuery project released jQuery 4.0.0, its first major version update in almost a decade. This release represents a clear shift away from legacy browser behavior and toward modern web standards, security expectations, and streamlined APIs.

For teams maintaining long-lived applications, jQuery 4.0 is both an opportunity and a checkpoint: it modernizes the library, but it also requires deliberate planning to upgrade safely.

‍

What’s New in jQuery 4.0.0

Legacy Browser Support Has Been Reduced

jQuery 4.0 officially drops support for several older platforms, including Internet Explorer 10 and earlier, Edge Legacy, and outdated mobile browsers. Internet Explorer 11 remains supported for now, but the direction is clear: jQuery is aligning with modern browser baselines.

This change simplifies the codebase and reduces the need for legacy workarounds that no longer reflect how the web is used today.

‍

Stronger Security Defaults

jQuery 4.0 introduces support for Trusted Types, improving compatibility with strict Content Security Policy configurations. This helps reduce the risk of cross-site scripting issues in environments that enforce modern browser security controls.

For security-conscious organizations, this is one of the most important improvements in the release.

‍

Codebase Modernization

A significant amount of deprecated and legacy code has been removed in jQuery 4.0. This includes older utility methods and long-deprecated APIs that were retained primarily for backward compatibility.

Internally, the project has moved further toward modern JavaScript patterns, including ES module usage, making jQuery easier to integrate with current build pipelines.

‍

A Smaller, More Focused Slim Build

The jQuery slim build has been further reduced by removing deferred objects and callbacks in favor of native JavaScript Promises. This reflects the reality that modern browsers provide robust native async support.

‍

Breaking Changes to Be Aware Of

Because this is a major version release, jQuery 4.0 removes behavior that existed in jQuery 3.x:

• Deprecated APIs that were previously retained are no longer available
• Certain internal behaviors and undocumented edge cases have been cleaned up
• Event handling now follows web standards more strictly, rather than jQuery’s historical custom behavior
  
  

While many applications will upgrade with minimal changes, teams should expect some refactoring if their code relies on older patterns.

‍

How to Approach a jQuery 4.0 Upgrade

The safest way to upgrade is incremental:

1. Audit your existing jQuery usage
   
   
2. Use migration tooling to identify deprecated APIs
   
   
3. Update affected code paths in development
   
   
4. Test thoroughly before deploying to production
   
   

This approach minimizes risk and avoids surprise regressions caused by removed functionality.

‍

Why jQuery 4.0 Matters in 2026

Despite the rise of modern frameworks, jQuery remains deeply embedded across the web — especially in long-running enterprise systems, CMS platforms, and internal tools.

jQuery 4.0 brings those environments closer to modern standards by:

• Reducing legacy technical debt
  
  
• Improving security posture
  
  
• Aligning with current browser capabilities
  
  

For many teams, upgrading to jQuery 4.0 is a practical modernization step even if a full framework migration is not on the roadmap.

‍

FAQ: jQuery 4.0.0

Q: Is jQuery 4.0 a drop-in replacement for jQuery 3.x?
A: Not entirely. While many APIs remain unchanged, deprecated features and legacy behaviors have been removed. Testing and some refactoring may be required.

Q: Which browsers does jQuery 4.0 support?
A: jQuery 4.0 targets modern browsers and removes support for older legacy platforms. Internet Explorer 11 remains supported for now.

Q: What security improvements are included in jQuery 4.0?
A: jQuery 4.0 adds support for Trusted Types and improves compatibility with strict Content Security Policy configurations, reducing XSS risk.

Q: How should teams prepare for upgrading?
A: Teams should audit their codebase, identify deprecated usage, update affected areas, and test thoroughly before rolling out jQuery 4.0 in production.

Q: Should new projects still use jQuery?
A: jQuery 4.0 is well-suited for maintaining and modernizing existing applications. For new projects, teams should evaluate frameworks that best match their long-term architecture.

Q: What if we can’t upgrade to jQuery 4.0 yet — can we stay on jQuery 3.x?
A. Yes. Some organizations remain on jQuery 3.x because of application complexity, third-party dependencies, or long upgrade timelines. In those cases, teams may use third-party extended security support, such as HeroDevs Never-Ending Support (NES), to continue receiving security fixes for newly disclosed vulnerabilities while planning a future upgrade.

‍