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:focus selector filter?

in Developing jQuery Core • 10 years ago

Since querySelectorAll has native support for :focus to find the
focused element, does it make sense to add support for the older
browsers? I can tell you that this is a common request on #jquery.
$.expr[':'].focus = function(a){ return (a ==
document.activeElement); }
This works in ie6+, ff3+, chrome2+, saf4+, opera9+, both with and
without qSA.
So the question is: is adding this worth the non-compatibility with
FF2, Chrome1, and Safari 3? Something that can be resolved through
proper documentation, perhaps.
Also, AFAICT, only the elements that support tabindex work with this
filter:
A, AREA, BUTTON, INPUT, OBJECT, SELECT, and TEXTAREA.

Replies(3)

alanhogan

Re: :focus selector filter?

9 years ago

Hey, Paul. Great post.

Just want to weigh in here, that unless there is a good reason not to, I think this is a good idea. I used ':focus' in a jQuery selector without giving it a second thought — it worked in the browsers I tested and I didn’t even think to check if jQuery officially supported :focus or not, because hey, it’s a legal CSS selector.

But one of our users, still on Firefox 3.0, complained that the site stopped working. Lo and behold, he gets an exception whenever we use :focus as a part of a selector in jQuery.

So backporting this to old browsers would absolutely be one fewer thing to worry about, as a developer.

I’m not terribly familiar with the core but clearly this would need optimized to use browser support whenever available if it’s faster than the document.activeElement test above.