WebKitCSSMatrix and ehow.com and web compatibility stuff

24 Feb 2015

Wow, early January late February 2015, time to blog about more exciting web compatibility bugs.

Lately we’ve been receiving a number of reports, both in Bugzilla and on webcompat.com, that ehow.com isn’t working in Firefox mobile browsers. With compelling articles like How to blog for cash and How to do your own SEO for your blog or website, this is not a great situation for my fellow Firefox Mobile-using-“how-to-get-rich-by-web-logging” friends.

And now for a brief message from our sponsor, http://vart.institute/: go learn about Art and programming and Mary Cassatt. // TODO(mike): ask jenn for money or how to do SEO.

The biggest obstacle to getting the site to behave is: ReferenceError: WebKitCSSMatrix is not defined. There are few minor CSS issues, but nothing that sprinkling a few unprefixed properties won’t solve.

If you’re not familiar with WebKitCSSMatrix, Apple has some docs. It’s pretty cool (and much nicer than using regular expressions to dice up serialized transform matrices and then doing math and string wrangling yourself). Microsoft even has an equivalent called MSCSSMatrix (which WebKitCSSMatrix is mapped to for compat reasons).

Once upon a time, this thing was specced as CSSMatrix in the CSS3 2D Transforms spec, but eventually was removed (because I forget and am too lazy to search through www-style archives). It returned as a superset of CSSMatrix and SVGMatrix and got the sweet new name of DOMMatrix—which now allows it to be mutuble or immutable, depending on your needs, i.e., do I want a billion new object instances or can I just modify this thing in place.

There’s a handful of polyshims available on GitHub if you need them, but the simplest is to just map WebKitCSSMatrix to DOMMatrix, which is supported in Firefox since Gecko 33.

Impress your friends like so:

if (!'WebKitCSSMatrix' in window && window.DOMMatrix) {
  window.WebKitCSSMatrix = window.DOMMatrix;

In theory that’s cool and useful, but if you do a little bit more digging you’ll find that it only gets you so far on the web. Back to ehow.com, here’s the code that powers the PageSlider class here:

function r() {
  var e = document.defaultView.getComputedStyle(E[0], null),
  t = new WebKitCSSMatrix(e.webkitTransform);
  return t.m41

// some method does W.At = r()
// then some other method calls d(W.At + o, 'none')

function d(e, t) {
  var n = 'none' != t ? 'all ' + t + 's ease-out' : 'none';
  E[0].style.webkitTransition = n,
  E[0].style.webkitTransform = 'translate3d(' + e + 'px,0,0)'

Unfortunately, WebKitCSSMatrix and webkitTransform aren’t really possible to tease apart, if you’re trying to be compatibile with the deployed web. So a straightforward WebKitCSSMatrix to DOMMatrix mapping won’t get you very far.