On Wed, 01 Apr 2015 06:57:43 +0200, Kyle Simpson <get...@gmail.com> wrote:
There are features being added to the DOM/web platform, or at least
under consideration, that do not have reasonable feature tests
obvious/practical in their design. I consider this a problem, because
all features which authors (especially those of libraries, like me) rely
on should be able to be tested if present, and fallback if not present.
Paul Irish did a round-up awhile back of so called "undetectables" here:
https://github.com/Modernizr/Modernizr/wiki/Undetectables
I don't want to get off topic in the weeds and/or invite bikeshedding
about individual "hard to test" features.
I think we should not design a new API to test for features that should
already be testable but aren't because of browser bugs. Many in that list
are due to browser bugs. All points under "HTML5" are browser bugs AFAICT.
Audio/video lists some inconsistencies (bugs) where it makes more sense to
fix the inconsistency than to spend the time implementing an API that
allows you to test for the inconsistency.
So I just want to keep this discussion to a narrow request:
Can we add something like a "feature test API" (whatever it's called)
where certain "hard" cases can be exposed as tests in some way?
Apart from <link rel=preload>, which features in particular?
The main motivation for starting this thread is the new `link
rel=preload` feature as described here: https://github.com/w3c/preload
Specifically, in this issue thread:
https://github.com/w3c/preload/issues/7 I bring up the need for that
feature to be testable, and observe that as currently designed, no such
test is feasable. I believe that must be addressed, and it was suggested
that perhaps a more general solution could be devised if we bring this
to a wider discussion audience.
I'm not convinced that a general API solves more problems than it causes.
The feature test API is bound to have bugs, too.
A good way to avoid bugs is with test suites. We have web-platform-tests
for cross-browser tests.
For <link rel>, we could solve the feature-testing problem by normalizing
the case for supported keywords but not unsupported keywords, so you can
check with .rel or .relList:
function preloadSupported() {
var link = document.createElement('link');
link.rel = 'PRELOAD';
return link.rel == 'preload';
}
--
Simon Pieters
Opera Software
