Microsoft has recently announced dropping IE<11 support completely in January 2020, including on Windows Server & Embedded versions. IE 11 will be made available to those supported systems that only had access to Internet Explorer 10 until now.

It seems jQuery 4.0 might be where we'd like to drop IE<11 support. When evaluating that, remember we're not releasing 4.0 right now but most likely closer to 2020 so the situation will make it more & more realistic. And with our strategy to reduce browser support only in major releases, if we don't drop those versions we'll be stuck with them for a long time.

Dropping IE<11 support could help a lot with the big planned refactors, like a rewrite of the event system that gets us closer to native and dropping Sizzle in favor of a smaller querySelectorAll wrapper with selector rewriting to work around issues.

Market share of IE<11 seems very low even right now. StatCounter data shows global IE 10 usage at 0.15% and IE 9 at 0.36%. Even in countries with historically high IE usage like China IE 10 & IE 9 already have small market share. In South Korea IE 11 has high usage at 20.1% but IE 10 - only 0.40% and IE 9 - only 0.18%.

Event netmarketshare.com, which historically shown way higher IE usage than StatCounter, shows all IE<11 versions combined had market of 1.13% in January, 2019.

Let's look at some other popular tools. Most of the ones I checked either already support only IE 11 or no IE at all or plan to drop IE<11 support in their next versions.

• UI libraries
  • jQuery UI stopped testing on IE<11 more than 2 years ago.
  • Semantic UI supports IE 11 only.
  • Materialize supports IE 11 only.
  • Material UI supports IE 11 only.
  • Bootstrap 4, released a year ago supports IE 10+. Currently it seems to plan to drop all IE versions in v5, together with no longer depending on jQuery.
  • Foundation supports IE 9+ but plans to only support IE 11 in the next version.
  • Pure.css supports IE 8+. As far as I understand, it's a CSS-only library.
  • UIKit supports IE 11 only.
  • Skeleton officially supports IE 11 only but declares it may work in older versions.
• Frameworks
  • React supports IE 9+ but requires polyfills for Map & Set .for IE<11 and requestAnimationFrame for IE 9. It also seems likely from various discussions that the next major version of React may drop IE<11.
  • Angular supports IE 9+. It's the only framework in the list where I couldn't find information about plans to drop IE<11. IE 9 support, in particular, requires the app to load many polyfills.
  • AngularJS supports IE 9+ but currently it's on life support, only receiving security fixes for the next ~2.5 years.
  • Vue.js supports IE 9+. The next version will only support IE 11 and in a limited way.
  • Ember dropped support for IE<11 a year ago
• Utility libraries
  • Lodash supports IE 9+, but version 5 will only support IE 11
  • Three.js support is not clear; only IE 11 works with the WebGL renderer which is faster & has more features than the other ones. Older browsers should work with other renderers; it's not specified how far the support goes, though.
  • D3.js v5 doesn't support IE at all
  • Axios, a popular HTTP library, supports IE 11 only
  • Moment.js supports IE 9+
• Tools to prepare test cases:
  • JSFiddle doesn't support editing in IE, but seems to work in view mode in IE 11. It breaks in IE 9-10
  • CodePen doesn't support editing in IE. Its preview works even in IE 9, but unofficially.
  • JS Bin works in IE 9+
  • Plunker works in IE 11

What do you think?