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Bug 25428 - hasFeature removal was premature
Summary: hasFeature removal was premature
Alias: None
Product: WebAppsWG
Classification: Unclassified
Component: DOM (show other bugs)
Version: unspecified
Hardware: PC All
: P2 normal
Target Milestone: ---
Assignee: Anne
QA Contact: public-webapps-bugzilla
Depends on:
Reported: 2014-04-23 13:52 UTC by Philip Jägenstedt
Modified: 2015-08-03 13:02 UTC (History)
5 users (show)

See Also:


Description Philip Jägenstedt 2014-04-23 13:52:59 UTC
hasFeature was made to always return true on my request.

It looks like I underestimated just how much the use counter data can change when it reaches the stable channel:

Removing hasFeature entirely is hopeless, and making it always return true is also right above the highest threshold (0.06%) ever cited for Blink.

It would be very interesting to learn what the features that return false are, but there's no way of collecting strings with the use counter system...

Sadly, I think the path of least resistance is to just go back to special-casing SVG.
Comment 1 Philip Jägenstedt 2014-04-29 22:11:27 UTC
Huh, something strange has happened in

The counts dropped from above 0.06% to around 0.004% between April 24 and 26. I have no idea how that could happen, will consult blink-dev.
Comment 2 Philip Jägenstedt 2014-04-30 09:30:39 UTC
Here's the blink-dev thread:

Since it's not clear what's going on, I suggest waiting for a few weeks or months before drawing any conclusions from the data.

In the meanwhile, Anne, do you think Mozilla would be willing change hasFeature to always return true if the usage turns out to be really low?
Comment 3 Olli Pettay 2014-04-30 09:51:37 UTC
Would need to add some telemetry. Since the special cases are for svg, 
even low usage could mean breaking quite large portion of svg content.
So better to have telemetry for svg part only and compare
true and false return value counts.
Comment 4 Philip Jägenstedt 2014-07-29 22:52:40 UTC
Chrome's use counter has stayed around 0.004% until now. In Chrome, SVG is used on around 10% of page loads, so even relative to that it's look good:

Any luck with telemetry in Firefox?
Comment 5 Philip Jägenstedt 2015-08-03 13:02:13 UTC
hasFeature() always returns true now, was in Chromium M44, and Chrome 44 was recently released. I'll close this and revisit only if there are regressions reported.