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Re: [DOM4] Short and Efficent DOM Traversal

From: Jonas Sicking <jonas@sicking.cc>
Date: Sat, 27 Jul 2013 20:38:28 -0700
Message-ID: <CA+c2ei-YW3ngHFGUXRrZQHpKQprx23AbSRtH+P0eaLXRYkD8Zg@mail.gmail.com>
To: François REMY <francois.remy.dev@outlook.com>
Cc: "public-webapps@w3.org" <public-webapps@w3.org>, DOM WG <www-dom@w3.org>
On Jul 27, 2013 6:55 PM, "François REMY" <francois.remy.dev@outlook.com>
> TL/DR: CSS Selectors represent the most commonly used way to perform
search in the DOM. But, until now, you’ve to choose between using CSS
(querySelectorAll) or doing incremental search (createTreeWalker). I think
we should try to fix that.
> The proposal here would be to accept CSS selectors in replacement to the
existing whatToShow flags {which are difficult to use and not entirely
satisfying}, i.e. overloading the createTreeWalker/createNodeIterator
functions to take a CSS Selector in the form of a string as a second
>> var tw = document.createTreeWalker(document.body, “ul.menu > li”);
>> while(tw.nextNode()) {
>>    if(...) break;
>>    ...
>> }
> Advantages:
> It’s much faster than to use a javascript function as a filter that
would call again the browser stack to find out whether a CSS selector match
or not a specific element
> We do not loose the ability to provide a more complex piece of javascript
if we really need it, but we reduced the cases where we need one.
> It’s less code to write (CSS is more efficient than any piece of JS)
> It allows getting rid of the long named constants nobody likes to use
> In addition, it would open huge optimization opportunities for the
browser (like skipping siblings that look similar, not entering into
descendants if it’s known a certain css class is not present among them,
reusing cached lists of elements matching a selector, or whatever).
> Thougths?

Unfortunately the treewalker and nodeiterator both carry weird baggage.

They are both very java-esq in design.

The TreeWalker can walk in a treelike manner or iterate as a list, and
follows nodes if they are moved out of the Document. The NodeIterator can
just iterate as a list but has an anchoring feature that keeps it in the
main Document tree at all times.

Why are those two features linked?

Also, modifying the existing TreeWalker/NodeIterator will make feature
detection harder.

I like the idea of being able to get lazy iterators and treewalkers. And
that are driven by selectors. But I think creating a new feature rather
than trying to retrofit existing ones will be more successful.

/ Jonas
Received on Sunday, 28 July 2013 03:38:56 UTC

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