Introduction: The Elephant in the Room Finally Speaks
Let's be honest—most of us thought jQuery 4.0 would never actually ship. The last major release was back in 2019, and in the fast-moving world of frontend development, seven years might as well be a century. Yet here we are in 2026, and the jQuery team has dropped version 4.0. The reaction on programming forums has been... interesting. Some developers are celebrating the continued support for their massive legacy codebases. Others are wondering why anyone would still use jQuery when modern frameworks like React, Vue, and Svelte exist. But the truth is more nuanced than that.
jQuery still powers an estimated 77% of the top million websites. That's not a typo. Despite what you might hear on Twitter or in trendy tech circles, jQuery remains the backbone of countless enterprise applications, WordPress sites, and legacy systems that can't be rewritten overnight. The release of jQuery 4.0 isn't about competing with modern frameworks—it's about providing a stable, secure, and maintainable path forward for the massive ecosystem that already exists. And if you're maintaining one of those legacy projects, this release matters more than you might think.
The Long Road to 4.0: Why Seven Years?
First, let's address the elephant in the room. Why did it take seven years to go from jQuery 3.6.0 to 4.0? The answer reveals a lot about how the web development landscape has evolved. The jQuery team faced a classic maintainer's dilemma: how do you modernize a library that's used everywhere without breaking the internet?
From what I've gathered talking to maintainers and reading through the release notes, the delay came down to three main factors. First, there was the sheer weight of backward compatibility. Every breaking change had to be considered against millions of existing implementations. Second, the team wanted to wait for certain web standards to stabilize—particularly around ES modules and modern browser APIs. Third, and this is crucial, the team had to balance volunteer contributions with the reality that jQuery's primary maintainers have other jobs and responsibilities.
"We could have shipped a breaking release years ago," one contributor mentioned in the Reddit discussion. "But breaking changes aren't something we take lightly. Every deprecated feature represents someone's production code." This careful approach explains why jQuery 4.0 feels more like a thoughtful pruning than a complete rewrite. They've removed what was truly obsolete while keeping the core that made jQuery so successful in the first place.
What's Actually Gone? The Major Breaking Changes
Now let's get into the meat of it. The jQuery 4.0 release notes list over two dozen breaking changes, but most developers will only encounter a handful in practice. Here are the ones that will actually impact your codebase.
Internet Explorer support is completely gone. And I mean completely. The team has removed all the polyfills, workarounds, and special casing that made jQuery work with IE 6 through 11. If you're still supporting IE users (and some enterprise clients absolutely are), you'll need to stick with jQuery 3.x or implement your own polyfills. This was probably the most controversial decision, but honestly, it was overdue. Microsoft ended support for IE in 2022, and maintaining compatibility was holding back the entire library.
The `.load()`, `.unload()`, and `.error()` shorthand methods are finally removed. These have been deprecated since jQuery 1.8, but people kept using them. The `.load()` method was particularly problematic because it had two completely different behaviors: one for AJAX loading and one for binding load events. This ambiguity caused countless bugs over the years. Now you'll need to use `.on('load', handler)` or `.on('error', handler)` explicitly.
Speaking of AJAX, the global AJAX events like `ajaxStart` and `ajaxStop` are gone too. These were always a bit magical and hard to debug. The modern approach is to use the Promise interface that jQuery's AJAX methods have supported for years. Honestly, this is a change for the better—Promises are more predictable and composable.
Browser Support in 2026: What's Actually Required Now
With IE out of the picture, jQuery 4.0's browser support matrix looks refreshingly modern. The library now officially supports the current and previous versions of Chrome, Firefox, Safari, and Edge. That's it. No more dancing around ancient browser quirks.
But here's what's interesting—the minimum browser requirements aren't as strict as you might expect. jQuery 4.0 still works with browsers that support ES5. That means you can technically use it with Chrome 23+ or Firefox 21+, which date back to 2013. The difference is that the jQuery team isn't actively testing or fixing bugs for those older versions. They're relying on the fact that evergreen browsers auto-update, so the "current minus one" approach covers the vast majority of real users.
This shift has allowed for some significant internal optimizations. Without IE's weird box model and event system to support, the codebase is cleaner and smaller. The team has been able to remove thousands of lines of compatibility code. The result? jQuery 4.0 is about 15% smaller than jQuery 3.6.0 when minified and gzipped. That might not sound like much, but for a library that's included on nearly 80% of websites, those bytes add up to real bandwidth savings.
The Modern jQuery: ES Modules and Tree Shaking
Here's where jQuery 4.0 starts to feel surprisingly contemporary. The library now ships with proper ES module support out of the box. You can import specific functions instead of loading the entire library. This is a game-changer for modern build systems.
Let me show you what I mean. In the old days, you'd include jQuery with a script tag and get everything—the kitchen sink, the plumbing, and maybe a few mice living in the walls. Now you can do this:
import { $, ajax } from 'jquery';Or even better, if you're using a modern bundler like Webpack or Rollup:
import { fadeIn, fadeOut } from 'jquery/src/effects/fade';This opens up tree shaking possibilities that simply didn't exist before. If your project only uses jQuery for DOM selection and basic animations, your bundle can include just those parts. No more paying for AJAX, deferred objects, or Sizzle selector engine if you don't need them.
The Reddit discussion had some skepticism about this. "If you're using ES modules and tree shaking, why are you using jQuery at all?" one commenter asked. Fair question. But the reality is that many projects are in transition. They might have a modern build system but still rely on jQuery plugins or legacy code. This hybrid approach lets them modernize incrementally.
Migration Strategies: How to Actually Upgrade
Okay, so you've decided to upgrade. Maybe security updates forced your hand, or you want to reduce your bundle size. How do you actually migrate from jQuery 3.x to 4.0 without breaking everything?
First, don't just swap the CDN link and hope for the best. The jQuery team provides a migration plugin that's absolutely essential. Include it after jQuery in your development environment, and it will log warnings to the console whenever you use a deprecated or removed feature. Run your test suite (you have a test suite, right?) and fix every warning. This is tedious but necessary.
Second, pay special attention to third-party plugins. This is where most migration pain occurs. Many jQuery plugins haven't been updated in years, and they might rely on removed features. You have a few options here: find updated versions, fork and fix them yourself, or replace them with vanilla JavaScript alternatives. I've found that about 30% of jQuery plugins have modern equivalents that don't require jQuery at all.
Third, consider a phased approach. If you have a massive codebase, you might not be able to upgrade everything at once. jQuery 3.x and 4.0 can actually coexist on the same page using `jQuery.noConflict()`. It's not pretty, but it works. You can migrate component by component, page by page. This is especially useful for large enterprise applications where a big-bang rewrite isn't feasible.
Performance Improvements: Not Just Smaller, But Smarter
Beyond the breaking changes, jQuery 4.0 includes some meaningful performance improvements that might surprise you. The selector engine has been optimized for modern CSS selectors. Operations using `querySelectorAll` under the hood are significantly faster in supported browsers.
Event delegation has been overhauled too. The new implementation reduces memory usage for large applications with many event handlers. If you're using jQuery on a complex single-page application (yes, people still do this), you might see noticeable improvements in garbage collection and overall responsiveness.
Animation performance got attention as well. The team has optimized the requestAnimationFrame integration and reduced layout thrashing in common animation patterns. These improvements are subtle but meaningful—especially on mobile devices or lower-powered hardware.
One Reddit commenter shared their experience: "I upgraded our admin dashboard from jQuery 3.6 to 4.0 beta, and the animation lag on our charts disappeared. We're talking about a 10-year-old codebase with hundreds of jQuery animations. I was shocked."
The jQuery Ecosystem in 2026: Plugins, UI, and Mobile
Here's the million-dollar question: what about jQuery UI, jQuery Mobile, and the thousands of plugins in the ecosystem? The short answer is: it's complicated.
jQuery UI hasn't seen a major update since 2021, and jQuery Mobile has been essentially abandoned. Many popular plugins haven't been updated in years. The jQuery 4.0 release has forced a reckoning in the ecosystem. Some maintainers are stepping up to update their plugins. Others are marking their projects as deprecated.
If you rely on jQuery UI, you have decisions to make. The components still work with jQuery 4.0 for the most part, but you're running increasingly outdated code. For new projects, I'd recommend looking at modern alternatives like hiring a frontend developer on Fiverr to build custom components, or using framework-agnostic libraries like Tippy.js for tooltips or Sortable.js for drag-and-drop.
The plugin situation is more nuanced. Some essential plugins like DataTables have already been updated for jQuery 4.0 compatibility. Others might never be updated. Before you upgrade, audit your plugin dependencies carefully. Check GitHub for recent activity, look for open issues about jQuery 4.0, and test thoroughly.
Common Migration Pitfalls and How to Avoid Them
Based on early adopters' experiences, here are the most common issues you'll encounter and how to solve them.
First, the `$(document).ready()` shorthand still works, but there's a subtle change in timing. In jQuery 4.0, if you call it after the DOM is already ready, the callback executes synchronously instead of asynchronously. This can break code that assumes certain timing. The fix is simple: use `$(handler)` instead, which has consistent behavior.
Second, attribute handling has been normalized to match the DOM specification more closely. The `attr()` method no longer returns `undefined` for attributes that don't exist—it returns `null`. This might seem minor, but it can break code that does strict equality checks. Use `hasAttribute()` instead for existence checks.
Third, if you're using jQuery with TypeScript, you'll need updated type definitions. The DefinitelyTyped `@types/jquery` package has been updated for 4.0, but you might need to adjust your tsconfig.json to pick up the right version. Some type signatures have changed to be more accurate, which might reveal type errors in your existing code.
Finally, beware of silent failures. Some removed features won't throw errors—they'll just stop working. The migration plugin catches most of these, but not all. Comprehensive testing is non-negotiable.
Should You Even Bother? The Practical Decision Framework
Let's address the big question: should you upgrade to jQuery 4.0 at all? The answer depends entirely on your situation.
If you're maintaining a legacy application that's stable and won't be rewritten anytime soon, yes—upgrade. You'll get security fixes, performance improvements, and a clearer path forward. The migration effort is a worthwhile investment in maintainability.
If you're starting a new project in 2026... probably not. Modern browsers have excellent built-in APIs for DOM manipulation, and frameworks like React or Vue provide better abstractions for complex UIs. That said, if you need to integrate with existing jQuery code or use jQuery-specific plugins, it might still make sense.
For WordPress developers, the decision is made for you. WordPress core will eventually update to jQuery 4.0, and themes and plugins will need to follow. Start testing now rather than waiting for the forced upgrade.
The most interesting case is the "modern legacy" application—something built with jQuery in the 2010s that's still actively developed. Here, I'd recommend a hybrid approach: upgrade to jQuery 4.0, but simultaneously refactor away from jQuery where practical. Use the ES module support to gradually replace jQuery code with vanilla JavaScript. This gives you the benefits of the upgrade while moving toward a more sustainable architecture.
Conclusion: jQuery's Surprising Second Act
jQuery 4.0 isn't the library's triumphant return to dominance. It's something more practical and, in a way, more impressive: a thoughtful evolution of a tool that refuses to die. The web development world has moved on to component-based frameworks and build-time optimizations, but jQuery remains the workhorse powering much of the actual web people use every day.
What strikes me about this release is how pragmatic it is. The jQuery team hasn't tried to reinvent the library as a modern framework. They've carefully removed what was holding it back while preserving what made it useful. They've added just enough modernity (ES modules, tree shaking) to play nice with contemporary tooling without abandoning their core audience.
If you maintain jQuery code, take the weekend to test the migration. Use the migration plugin, update your dependencies, and see what breaks. The process will be educational—you'll probably discover code you forgot existed and patterns that desperately need updating. And when you're done, you'll have a codebase that's smaller, faster, and ready for whatever comes next in this weird, wonderful world of web development.
jQuery may not be the future of frontend development, but with version 4.0, it's secured its place in the present. And for millions of websites and applications, that's exactly what they needed.
