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Re: QSA, the problem with ":scope", and naming

From: Ojan Vafai <ojan@chromium.org>
Date: Wed, 19 Oct 2011 19:22:23 -0700
Message-ID: <CANMdWTu3TerRJqmz3i-hpkta6YsLFggN3mBM0tEq730XPXt1cg@mail.gmail.com>
To: Jonas Sicking <jonas@sicking.cc>
Cc: Alex Russell <slightlyoff@google.com>, Webapps WG <public-webapps@w3.org>, Yehuda Katz <wycats@gmail.com>, John Resig <jeresig@gmail.com>, Paul Irish <paulirish@google.com>, Lachlan Hunt <lachlan.hunt@lachy.id.au>
On Wed, Oct 19, 2011 at 7:07 PM, Jonas Sicking <jonas@sicking.cc> wrote:

> On Tue, Oct 18, 2011 at 9:42 AM, Alex Russell <slightlyoff@google.com>
> wrote:
> > Lachlan and I have been having an...um...*spirited* twitter discussion
> > regarding querySelectorAll, the (deceased?) queryScopedSelectorAll,
> > and ":scope". He asked me to continue here, so I'll try to keep it
> > short:
> >
> > The rooted forms of "querySelector" and "querySelectorAll" are
> mis-designed.
> >
> > Discussions about a Scoped variant or ":scope" pseudo tacitly
> > acknowledge this, and the JS libraries are proof in their own right:
> > no major JS library exposes the QSA semantic, instead choosing to
> > implement a rooted search.
> >
> > Related and equally important, that querySelector and querySelectorAll
> > are often referred to by the abbreviation "QSA" suggests that its name
> > is bloated and improved versions should have shorter names. APIs gain
> > use both through naming and through use. On today's internet -- the
> > one where 50% of all websites include jQuery -- you could even go with
> > element.$("selector") and everyone would know what you mean: it's
> > clearly a search rooted at the element on the left-hand side of the
> > dot.
> >
> > Ceteris peribus, shorter is better. When there's a tie that needs to
> > be broken, the more frequently used the API, the shorter the name it
> > deserves -- i.e., the larger the component of its meaning it will gain
> > through use and repetition and not naming and documentation.
> >
> > I know some on this list might disagree, but all of the above is
> > incredibly non-controversial today. Even if there may have been
> > debates about scoping or naming when QSA was originally designed,
> > history has settled them. And QSA lost on both counts.
> >
> > I therefore believe that this group's current design for scoped
> > selection could be improved significantly. If I understand the latest
> > draft (http://www.w3.org/TR/selectors-api2/#the-scope-pseudo-class)
> > correctly, a scoped search for multiple elements would be written as:
> >
> >   element.querySelectorAll(":scope > div > .thinger");
> >
> > Both then name and the need to specify ":scope" are punitive to
> > readers and writers of this code. The selector is *obviously*
> > happening in relationship to "element" somehow. The only sane
> > relationship (from a modern JS hacker's perspective) is that it's
> > where our selector starts from. I'd like to instead propose that we
> > shorten all of this up and kill both stones by introducing a new API
> > pair, "find" and "findAll", that are rooted as JS devs expect. The
> > above becomes:
> >
> >   element.findAll("> div > .thinger");
> >
> > Out come the knives! You can't start a selector with a combinator!
> >
> > Ah, but we don't need to care what CSS thinks of our DOM-only API. We
> > can live and let live by building on ":scope" and specifying find* as
> > syntactic sugar, defined as:
> >
> >  HTMLDocument.prototype.find =
> >  HTMLElement.prototype.find = function(rootedSelector) {
> >     return this.querySelector(":scope " + rootedSelector);
> >   }
> >
> >   HTMLDocument.prototype.findAll =
> >   HTMLElement.prototype.findAll = function(rootedSelector) {
> >     return this.querySelectorAll(":scope " + rootedSelector);
> >   }
> >
> > Of course, ":scope" in this case is just a special case of the ID
> > rooting hack, but if we're going to have it, we can kill both birds
> > with it.
> >
> > Obvious follow up questions:
> >
> > Q.) Why do we need this at all? Don't the toolkits already just do
> > this internally?
> > A.) Are you saying everyone, everywhere, all the time should need to
> > use a toolkit to get sane behavior from the DOM? If so, what are we
> > doing here, exactly?
> >
> > Q.) Shorter names? Those are for weaklings!
> > A.) And humans. Who still constitute most of our developers. Won't
> > someone please think of the humans?
> >
> > Q.) You're just duplicating things!
> > A.) If you ignore all of the things that are different, then that's
> > true. If not, well, then no. This is a change. And a good one for the
> > reasons listed above.
> >
> > Thoughts?
>
> I like the general idea here. And since we're changing behavior, I
> think it's a good opportunity to come up with shorter names. Naming is
> really hard. The shorter names we use, the more likely it is that
> we're going to break webpages which are messing around with the
> prototype chain and it increases the risk that we'll regret it later
> when we come up with even better functions which should use those
> names. Say that we come up with an even better query language than
> selectors, at that point .find will simply not be available to us.
>
> However, it does seem like selectors are here to stay. And as much as
> they have shortcomings, people seem to really like them for querying.
>
> So with that out of the way, I agree that the CSS working group
> shouldn't be what is holding us back. However we do need a precise
> definition of what the new function does. Is prepending ":scope " and
> then parsing as a normal selector always going to give the behavior we
> want? This is actually what I think we got stuck on when the original
> querySelector was designed.
>
> So let's get into specifics about how things should work. According to
> your proposal of simply prepending a conceptual ":scope" to each
> selector group, for the following DOM:
>
> <body id="3">
>  <div id="context" foo=bar>
>    <div id=1></div>
>    <div class="class" id=2></div>
>    <div class="withChildren" id=3><div class=child id=4></div></div>
>  </div>
> </body>
>
> you'd get the following behavior:
>
> .findAll("div")  // returns ids 1,2,3,4
> .findAll("")      // returns the context node itself. This was
> indicated undesirable
> .findAll("body > :scope > div")  // returns nothing
>

Wouldn't this return ids 1,2,3 if we're not prepending :scope as you say
below?


> .findAll("#3")  // returns id 3, but not the body node
> .findAll("> div") // returns ids 1,2,3
> .findAll("[foo=bar]") // returns nothing
> .findAll("[id=1]") // returns id 1
> .findAll(":first-child") // returns id 1
>
> Is this desired behavior in all cases except the empty string? If so
> this seems very doable to me. We can easily make an exception for the
> case when the passed in string contains no selectors and make that an
> error or some such.
>
> I do however like the idea that if :scope appears in the selector,
> then this removes the prepending of ":scope " to that selector group.
> Is there a reason not to do that?
>
> Additionally it seems to me that we could allow the same syntax for
> <style scoped>. But maybe others disagree?
>

Sounds good to me. A sticky case you left out is parent, sibling and
reference combinators.

.findAll("+ div")

Assuming the context node has siblings, should that return them? If so,
should it match siblings when using <style scoped>.

IMO, it shouldn't match anything in either case. We should assert that only
descendants of the scope element will ever be returned. This would also make
it naturally match <style scoped> where only descendants of the scope
element are ever affected.

I think appropriate optimizations as well as extensible functions
> should be out-of-scope for this thread. They are both big subjects on
> their own and we're approaching 50 emails in this thread.
>
> / Jonas
>
>
Received on Thursday, 20 October 2011 02:23:08 GMT

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