[META] Use data attributes rather than classes wherever possible

Quick and dirty solution. We can't use $().data() because this needs to be exposed to CSS and other JS on the page and we can get away with native selectors so everything works out well. There is a slight perf impact, about 4/5ms on chrome compared to using classes but not a big deal compared to what's going on inside the functions that are called with .once() and considering we're not messing with the styling is a big plus.

Ideally I'd like to enforce the use of an id (so you can't call $().once(function () {});) and remove the function parameter so that once is only used for filtering a set of jQuery objects (so you can't do $().once('my-one-and-only', function () {}))

The only valid way to use once would then be:

$(selector).once('one-and-only').each(something)

// or

var $elements = $(selector).once('one-and-only');

That's how it's done in core now anyway.

If you ask me, the once thing ought to be a no-jQuery script.

Ah sorry removed the auto increment thing in that patch, didn't mean to. Anyway it's NW really.

Ok before we get into API changes of jQuery.once() here is an API-compatible version that uses the data-drupal-once attribute to do it's magic.

With the patch.

> We can't use $().data() because this needs to be exposed to CSS and other JS on the page

jQuery Once's job is simply to act on an element once. If CSS needs to react in a certain way, then it should add a specific class accordingly:
``` javascript
$('.myelement').once().addClass('specialcase');
```

Thanks for the pull request. Let's talk over there:
https://github.com/RobLoach/jquery-once/pull/5

Let's keep changes upstream, put out a release, and then update it here afterwards.

Postponed on upstream.

recalculation of style??

I think it will:

for( var i = 0; i < 200; i++) {
 jQuery('a').addClass('active');
}

It won't

for( var i = 0; i < 200; i++) {
 jQuery('a').addClass('active' + i);
}

no active + i class in your stylesheets.

Re rolled.

The library has been changed upstream. We need to update our copy in core to the latest available code now.

Unless there is a tagged release already, it's fine if we're going to temporarily update to the latest master. — Since the change to upstream has not been battle-tested against real code/implementations, it's possible that we might even find bugs.

#2348321: Upgrade to jQuery Once 2.x

Moving this to be a META issue for all the cases we find where .data() could/should be used.

dup of several other issues. Now jquery once uses data attributes too.