jQuery 4.0 and the Modern Web

Should you upgrade to jQuery 4.0, or has native JavaScript finally made the library obsolete? With jQuery’s first major release in nearly a decade landing in January 2026, frontend developers maintaining existing applications face a practical decision: upgrade, stay put, or migrate away entirely.

This article breaks down what actually changed in jQuery 4.0, the real upgrade risks, and when modern jQuery still makes sense versus native JavaScript.

What Changed in jQuery 4.0

jQuery 4.0 modernizes the library’s foundation while removing accumulated legacy code. Here’s what matters for upgrade planning.

Browser Support Baseline

jQuery 4.0 drops Internet Explorer 10, Edge Legacy (pre-Chromium), and older mobile browsers. IE11 is still supported in this version, giving teams additional time to modernize before a future major release removes it.

The slim build goes further, removing Ajax modules and animation support for a smaller footprint. It also removes Deferreds, Callbacks, and queue, assuming native Promises in modern environments.

Modern Packaging

jQuery 4.0 introduces modern build tooling and package exports that improve compatibility with contemporary bundlers like Vite, Rollup, and webpack. If your build pipeline expects CommonJS or AMD, you may need adjustments—though most toolchains handle this automatically.

See the official jQuery 4.0 upgrade guide for environment details.

Security Improvements

jQuery 4.0 adds Trusted Types support and improves Content Security Policy compatibility. Previous versions could violate strict CSP configurations in certain API paths. For teams enforcing modern security policies, this is a meaningful improvement.

The release announcement outlines these security changes in more detail: jQuery 4.0.0 Release.

Removed APIs and Changed Behavior

Long-deprecated utilities are gone. The slim build removes Deferreds and Callbacks entirely, assuming native Promises. JSONP auto-promotion is removed in favor of explicitly using CORS or JSONP where intended. FormData now works automatically with jQuery.ajax.

The most subtle breaking change: focus/blur event ordering now follows W3C specifications rather than jQuery’s historical cross-browser normalization. Code relying on the old order may behave unexpectedly.

jQuery vs Native JavaScript: The Real Trade-off

The question isn’t whether native JavaScript can replace jQuery—it clearly can. The question is whether it should for your specific codebase.

When Native JavaScript Wins

For new projects, native APIs like document.querySelector(), fetch(), and classList cover most of what jQuery historically provided. Modern browsers implement these consistently. Performance is marginally better without the library overhead, and you avoid an external dependency.

If you’re building a greenfield application with a modern framework, adding jQuery creates unnecessary weight.

When jQuery Still Makes Sense

jQuery remains practical for:

• Legacy applications with extensive jQuery usage where rewriting isn’t justified
• Incremental modernization where you’re updating piece by piece
• Enterprise stacks with stable, long-lived codebases and plugin dependencies
• CMS platforms like WordPress where jQuery is already present

The large percentage of websites still running jQuery aren’t all technical debt—many are stable systems where the library continues to work fine.

Upgrading to jQuery 4: Key Risks

Upgrading from jQuery 3.x isn’t a drop-in replacement. Plan for these friction points:

Removed utilities: Audit your codebase for deprecated methods. The jQuery Migrate plugin identifies problematic patterns.

CSS unit handling: Some edge cases around unitless values have changed.

Event ordering: Test any code depending on focus/blur/focusin/focusout sequences.

Ajax behavior: FormData handling and JSONP changes may affect API calls.

Most applications upgrade with minimal changes, but “minimal” isn’t “zero.” Budget time for testing.

Should You Upgrade?

Upgrade if: You need improved CSP/Trusted Types support, plan to stay on jQuery long-term, or want current security updates.

Stay on 3.x if: Your application is stable, upgrade testing isn’t feasible, or you’re planning a framework migration anyway. Extended support options exist for teams that can’t upgrade immediately.

Skip jQuery entirely if: You’re starting fresh with a modern framework or your native JavaScript coverage is already sufficient.

Conclusion

jQuery 4.0 is a sensible modernization for teams committed to the library. It’s more secure and aligned with current browser standards. But it’s not a reason to adopt jQuery if you weren’t already using it.

For existing applications, evaluate the upgrade based on your security requirements, plugin dependencies, and testing capacity—not on whether jQuery is “still relevant.” For millions of production applications, it clearly is.

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