On element.dataset And data-* Attribute

Why on earth? I mean why we should put a data-whatever attribute into our layout? Where is the good old MVC? How can you consider data-* more semantic? more semantic than what? Why we would like to kill truly semantic pages and graceful enhancements? Why we need JavaScript redundant info inside nodes attributes but we cannot understand a script tag in the middle of the page? Why in the performances matter era we would like to let users download stuff that they will probably never use?

What Am I Talking About

We can find the "magic" data attribute description in the W3C Semantics, structure, and APIs for HTML documents page. These days there is a page that is going around even too much ... finally somebody realized that this data-thingy is nothing different than what we could have always used since ages: XML.

Why We Are Doing Wrong

If we are enthusiast about a custom attribute able to bring whatever information, we should ask ourself why on earth we are not using simply XML plus XLS to transform nodes with custom attributes. Each node can be easily and quickly transformed, in the client side as well and in a cross browser way, via one or more cached XSLT able to create runtime whatever we need.
We need to sort the music file list via data-length attribute? No problems at all, we can reorder via DOM every node we need and put the XML fragment transformed via XSLT into a single HTML node in that page. Moreover, we can use modular XSL to transform branches or specific cases ... but that is too clean and professional, isn't it?

Data Used Via Selectors

Let's say we have 3 songs with the same length, taking the example from W3 page, OK?

<ol>
  <li data-length="2m11s">Beyond The Sea</li>
  <li data-length="2m11s">Beside The Sea</li>
  <li data-length="2m11s">Be The Sea</li>
</ol>

First of all that example is quite hilarious, to make a sort as fast as possible that kind of representation is not ideal, is it?
It does not matter, the point is that as soon as this stuff will be implemented, all jQuery users will start to think so semantic that everything will become a:

$("@data-whatever=whatevervalue").each(...)

Seriously ... if we want to make the web the worst semantic place ever, just put in medium skilled developers this kind of weapon, and we'll scream in few months HTML5 Failed!
Who will care anymore about the appropriate element when everything can be easily validated in the W3 for totally dirty and useless, for non JS users, layouts?

The Namespace War Has Started Already

I can imagine lots of new devs starting to use the data as if it is their own attribute, ignoring conflicts problem we've always had with the global namespace. Move this problem into the DOM, and the Cactus Jam is ready to eat.
On the other hand how best practice will be a DOM loads of nodes with multiple data attributes?

<div
   data-jquery-pluginname-good-stuff="$(this).whatever()"
   data-dojo-loadsync="thisNodeFile"
   data-prototype-valueof="Object.prototype.valueOf=this"
/>

... I mean ... seriously, is this the HTML5 we are talking about? An empty element there just to make the anti semantic magic happen?

Dozens Of Different Ways

First of all querySelectorAll.
The document method we all were waiting for is finally 90% here and rather than use semantic and logic selectors to retrieve what we need and when we need, we prefer to make the DOM that dirty? Are we truly so monkeys that we cannot spot a list of songs and order them by their length that will be 99.9% of the time part of that song info and accordingly present in the DOM as context?
Where are classes? Where are external resources totally ignored by those users which aim is simply the one to surf quickly, or to crawl info? data-whatever?

Why We Don't Need data-*

First of all, classes. If we have a list of songs the class songlist in the single outer UL or OL node is everything we need to retrieve that list and order by title, duration, everything else present in that list, since in whatever grid we have ever used, we order by columns where we know the column content.
How can a user even decide to order by length if this length is not displayed?
How can he order by something not even showed?
It's like me in a shop asking to order by palm trees a list of sounds systems ... I think they'll look at me like a mad person and they would be right, don't you agree?
So, the semantic part of this attribute does not exist. The same example showed in the W3 draft is ridiculous for the reason I have already said. If the song length info is already in the DOM and properly showed we don't need redundant info for every user, we just need a good sort function for that list of songs and nothing else.

$.fn.sort = function(){
    // proof of concept, not even tested
    // written directly here in the blogger textarea
    // don't try at home but please try to understand the logic
    var li = Array.prototype.slice.call(this);
    li.sort(function(a, b){
        return
            $(a).find(".length").text() < 
            $(b).find(".length").text() ?
        1 : -1
    });
    return $(li).each(function(i, li){
        li.parentNode.appendChild(li);
    });
};
$(".songs li").sort();

Is above proof of concept that different from a $(".songs @data-length").sort() ? It's even shorter!

Map The DOM If Necessary

If we are struggling that much with this "so much missed data-*" we can still use the class to map common info ... how?

<ol class="songs">
  <li class="map-0">Beyond The Sea</li>
  <li class="map-0">Beside The Sea</li>
  <li class="map-1">Be The Sea</li>
</ol>

If we need to attach properties into a DOM node we can still use the class attribute.
Semantic, classifying the node as a mapped one, not redundant, letting us provide more than once same kind of info for different nodes, and lightweight, avoiding data description provided by the mapped object.
In few words, and always via JavaScript, we can attach a file with this content:

var map=[{
    length:"3m21s",
    artist:"Nature"
},{
    length:"2m59s",
    artist:"You"
}];

For each node, when necessary, we could simply retrieve the associated map in this way:

function nodeInfo(node){
    return map[
        (
            /(?:^|\s)map-(\d+)(?:\s|$)/.exec(node.className) ||
            [0,-1]
        )[1]
    ];
};

And that's it. Each mapped node will return an object or undefined when nodeInfo function is called. Again, all this stuff is a proof of concept, but can we agree that data-* is just the wrong response to solve a JavaScript problem that should be solved everywhere except into the HTML?