Happy 20th Birthday, jQuery! What's New in Version 4.0.0?

Happy 20th Birthday to jQuery!

Since John Resig released jQuery in 2006, this library has accompanied web development for two decades. Now, nearly ten years after its last major version release, the jQuery team has officially launched jQuery 4.0.0.

Many people might think jQuery is ready to retire from the stage of history. However, seeing the news of the official release of jQuery 4.0.0, one has to admit: a Ferrari is still a Ferrari, even as it ages.

This update isn't just a simple patch job. The team has cleaned up years of technical debt and removed outdated APIs, finally allowing this classic library to keep pace with the rhythm of modern web development.

Here are the most noteworthy changes in this update:

Saying Goodbye to Ancient Browsers

This is probably the most welcome change. jQuery 4.0.0 officially stops supporting IE 10 and below.

Currently, support for IE 11 is retained, but this is temporary; the team plans to completely remove IE support in the future jQuery 5.0. Additionally, support for Edge Legacy, iOS versions older than 11, Firefox versions older than 65, and old Android browsers has also been removed.

Unless you are working on "antique" projects, this means the package size will be smaller, and the execution speed will be faster.

Removing Outdated APIs

As native JavaScript (ES6+) capabilities have matured, many of jQuery's early helper functions have lost their meaning. Version 4.0 removes a large number of these APIs.

You should now use native equivalents:

• jQuery.trim is gone ➡️ Use String.prototype.trim()
• jQuery.isArray is gone ➡️ Use Array.isArray()
• jQuery.parseJSON is gone ➡️ Use JSON.parse()

Additionally, some array methods that were intended for internal use only (like push, sort, and splice) have been removed from the jQuery prototype. Developers should now use native JavaScript methods directly to replace these legacy features.

Source Code Migrated to ES Modules

The jQuery source code has finally migrated from the old AMD module system to ES Modules.

This allows jQuery to integrate much more smoothly into modern build toolchains like Vite, Rollup, or Webpack. Furthermore, you can now load and run jQuery directly in the browser via native modules, aligning with modern development workflows.

Focus Event Order Returns to W3C Standards

For a long time, different browsers disagreed on the trigger order of focus events (focus, blur, focusin, focusout). jQuery previously enforced its own order to unify behavior.

Now that all major browsers have reached a consensus, jQuery 4.0.0 has decided to stop intervening manually. It now directly follows the W3C standard order:

blur -> focusout -> focus -> focusin

Note: This is a breaking change! If your existing project relies heavily on a specific event trigger order, pay extra attention when upgrading.

A Lighter "Slim" Version

The new Slim version has removed the Deferreds and Callbacks modules, shrinking the size even further (reduced by about 8KB after gzip).

Since modern browsers (excluding IE11) natively support Promise, most asynchronous operations no longer need jQuery's Deferreds. If your project targets modern browsers, the Slim version will be the better choice.

Quick Start Experience

Even if it's not for a new project, many developers want to try out version 4.0 just for nostalgia's sake. The fastest way is to run a demo by installing jquery@4.0.0 via npm, which requires a stable and well-configured environment.

If you don't want to mess up your local setup with complex configurations just to try something new, or if you simply find setting up environments tedious, you can try ServBay. It allows you to deploy a Node.js environment with one click, automatically handling path configuration and version management.

Once the environment is set up, you can simply run npm commands in your directory to pull the latest jQuery and start playing around—saving both time and effort.

Conclusion

The release of jQuery 4.0.0 proves that it isn't "lying flat" (giving up). Instead, it is striving to adapt to modern web standards. It's like a martial arts master who went into seclusion for 10 years and emerged stronger than ever.

Whether for maintaining existing assets or for rapid development in specific scenarios, this new version delivers a solid performance.