Considering support for IE11

[zbran...@mozilla.com]

Hi all,

I've been working on assessing the work required to get l20n.js to work in IE11.

Unfortunately, IE11 is pretty far away from the JavaScript and DOM we use in l20n.js, so the amount of incompatibilities is pretty significant.

Here's the list:

1) Lack of support for 'for .. of'
2) Lack of support for template tag
3) Lack of support for Array.from
4) Lack of support for Promise
5) Set can't take an Array in constructor
6) Lack of support for WeakSet
7) Lack of support for Map.prototype.keys
8) Lack of support for navigator.languages
9) Lack of support for String.prototype.endsWith
1) Lack of support for FSI/PDI unicode escape points (display artifacts)

And that's just to get an example running. There seem to be more problems with Set/Map according to people trying to get polyfills to work.

Some of those things, like Promise, can be polyfilled. Some, like template tag, for .. of, WeakSet etc. cannot.

According to caiuse.com, IE11 has currently 6% of world marketshare. That market share did not change significantly since Q2 of 2014.

On top of that, IE11 is the very last of the old generation of web browsers that receive no update and that not have a user base that migrate to the new version in reasonable intervals.

That means that if we decide to support IE11, and try to set a tipping point at, say, 3% of market share for when we drop the support, I believe we will have to support IE11 for at least another two years. This is scary.

Because of terrible standards support and high number of unpatched vulnerabilities I believe that IE11 will have to be a subject to a world wide campaign similar to one that IE6 had.
I expect that with the Web moving forward at the current pace, the call to get rid of IE11 will happen soon.

Getting support for IE11 seems to me like a massive cost to our codebase and ability to move forward, significant time/effort cost, increase maintenance cost and, ultimately, path with no reward since IE11 is a dead product already and will become just more obsolete with every day passing.

For that reason, I'd like to suggest that we *do not* include support for IE11 and instead focus on supporting modern browsers, that will still require us to make compromises, like Edge and Safari 9, iOS 9 and Android 6.0.

zb.