jQuery 1.x vs jQuery 2.x: Browser Support Explained

When jQuery 2.0 was released in 2013, the primary distinction between the jQuery 1.x and 2.x branches was browser support. While jQuery 1.x maintained backward compatibility with legacy desktop browsers, jQuery 2.x completely removed support for Microsoft Internet Explorer 6, 7, and 8. This divergence allowed the jQuery team to create a lighter, faster version of the library tailored for modern web standards and emerging mobile platforms without breaking functionality for projects that still relied on older versions of Windows.

The Removal of Internet Explorer 6, 7, and 8

The definitive technical difference between the two branches was the treatment of legacy Internet Explorer:

  • jQuery 1.x: Maintained comprehensive polyfills, fixes, and workarounds for the quirks, non-standard event models, and missing DOM methods inherent to IE6, IE7, and IE8.
  • jQuery 2.x: Dropped all code paths, event normalization, and bug fixes specific to IE6–8. It treated Internet Explorer 9 and higher as the minimum baseline for the IE family.

Because IE6–8 did not support standard web technologies like addEventListener, standard CSS selectors, or native JSON handling, supporting them required massive amounts of boilerplate code. Eliminating this requirement was the sole objective of creating the 2.x branch.

Performance and File Size Reductions

Dropping legacy IE support yielded immediate technical advantages for jQuery 2.x:

  • Smaller File Size: Removing IE-specific hacks and patches reduced the library's uncompressed and minified file size by approximately 10–12%. This resulted in faster download, parsing, and execution times.
  • Cleaner Codebase: Developers working on the jQuery core could eliminate complex branching logic that checked for broken implementations of native browser APIs, improving overall runtime performance.
  • Mobile Optimization: jQuery 2.x was particularly targeted at mobile web browsers (such as iOS Safari and Android Browser), which never suffered from the quirks of desktop IE6–8 and benefited greatly from a lighter footprint.

API Consistency Across Branches

Despite the change in browser support, the jQuery core team maintained strict API parity between the two lines. jQuery 2.0 matched the API of jQuery 1.9, and subsequent releases (such as 1.10 and 2.1) mirrored features and public methods.

This design choice ensured that code written for jQuery 2.x was completely interchangeable with jQuery 1.x. Developers did not need to learn new functions or rewrite existing application logic to switch between the two branches.

Parallel Maintenance and Conditional Loading

Because millions of enterprise users and legacy environments still depended on IE8, the jQuery team maintained both branches concurrently for several years. Developers who needed to support both modern and legacy environments often implemented conditional comments in HTML to serve jQuery 2.x to modern browsers and fall back to jQuery 1.x for older clients:

<!--[if lt IE 9]>
    <script src="jquery-1.11.3.min.js"></script>
<![endif]-->
<!--[if gte IE 9]><!-->
    <script src="jquery-2.1.4.min.js"></script>
<!--<![endif]-->

This dual-branch strategy remained the standard until jQuery 3.0 was released in 2016, which unified the library into a single branch that permanently left IE6–8 support behind.