Add detect/tests for prefetch

[HeroProtagonist]

Closes #2536

• Made a detect for prefetch based on how to feature detect? w3c/preload#7
• Added general test and caniuse test

[robin-drexler]

Hey, just stumbled upon this. This check may exclude IE11 which appears to support prefetch, but not relList :(

This isn’t an issue for preload because IE supports neither.

[HeroProtagonist]

Do any of the detects do browser detection for a case like this?
I see a User Agent parser here, but not in source code

Modernizr/test/browser/integration/caniuse.js

Line 4 in 94592f2

var ua = new UAParser(navigator.userAgent).getResult();

[rejas]

creating a "rel" directory for this test only seems overkill. isnt there a better place for this?

[HeroProtagonist]

I can move it, just was thinking a follow up pr would be for rel=preload

[rejas]

Then I propose putting it in a "link" subdirectory, since it is a test on the link element ...

[HeroProtagonist]

done!

[rejas]

yeah, that UAparser is onyl used during testing of Modernizr to check against the caniuse database. It is generally not advised to use it in normal feature tests.

[HeroProtagonist]

yeah, that UAparser is onyl used during testing of Modernizr to check against the caniuse database. It is generally not advised to use it in normal feature tests.

Looks like navigator.userAgent is used in some detections. Maybe that is a better option

https://github.com/Modernizr/Modernizr/search?q=navigator.userAgent

[rejas]

Yes, that sounds reasonable :-)

[HeroProtagonist]

@rejas Added ie11 check using document.documentMode which is used in other parts of the code for similar IE specific detection

[rejas]

Thanks for the PR and your persistence :-) Merged!