Does the feature detector detector trigger on undefined accesses to *all* JavaScript objects, or just host objects?
On Tue, Aug 9, 2016 at 4:42 AM Manish Goregaokar <manishsm...@gmail.com> wrote: > Feature detection is often a pain point when figuring out why a site > doesn't work in Servo -- regular JS errors are logged and detectable, but > feature detection is silent. JavaScript's awesome coercion rules cause > similar issues when a property evaluates to false when it's really > undefined. > > To help find cases where feature detection is going on, I wrote a "feature > detector detector". Basically, it logs each time a property is accessed, > where that access evaluates to `undefined`. > > Some results can be found here > <https://gist.github.com/Manishearth/d3534fb65c65e4ef86f2152cf3bd2c0f>, > both with and without spoofing the UA to be firefox. > > To run, clone the "FDD" branch on my mozjs fork > <https://github.com/servo/mozjs/compare/master...Manishearth:FDD?expand=1 > >, > and set it as a path override (paths = ["/path/to/mozjs"] in > components/servo/.cargo/config). Building and running this on any site will > spew out tons of JSON output about each possible-feature-detection property > access. Run this output through parse.py > < > https://gist.github.com/Manishearth/06583087c4001f45ed3a9e74c7848211#file-parse-py > > > to filter it down to property accesses for properties that actually exist > in Firefox. The list of properties in parse.py is not 100% complete (see > the comment on gen.js. Also, Location is weird), but it's close enough. > > Should be useful to help find and prioritize features to work on. > > Firefox may also have interest in this, so I'm seeing if a cleaned-up > version of this might be something we can merge into the main codebase. > > Let me know if there are sites you'd like to see this run against! > > Thanks, > -Manish Goregaokar > _______________________________________________ > dev-servo mailing list > dev-servo@lists.mozilla.org > https://lists.mozilla.org/listinfo/dev-servo > _______________________________________________ dev-servo mailing list dev-servo@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-servo
