I've recently found on one of the sites opening tag like this:
<script data-ip="93.1xx.3.2x" data-backuri="something.com">
And I couldn't find any information about it. What are those tags used for?
data-* attributes are custom HTML attributes.
Basically, there are standard HTML attributes like style, src, width, height, class... and these have a special meaning to browsers and are 'reserved'.
However, custom attributes have no special meaning generally and are only special to the owner's application. They can be used to simplify an application's logic.
Using data- before your attribute name ensures that future standard attributes will not use your current attribute. For example, imagine today you are using a sound attribute but then the HTML standard adds a sound attribute meaning something other than what you meant. Had you used data-sound, you would have been fine because there would be no conflict. The specification says no future standard browser attributes will start with data-.
See jquery get HTML 5 Data Attributes with hyphens and Case Sensitivity for some useful info on why we use data-* attributes.
Also, see MDN docs for some useful information.
Related
There are very clear rules for how custom elements should be named. The main difference to other HTML elements is that they must have a non-leading hyphen. While it's possible to load an HTML document that includes made-up tag names that don't stick to these rules, it's supposed to guarantee a certain level of future-proofing and platform support.
However, I'm looking for guidance on how to name attributes for my custom elements. For readability and convenience I would prefer to use short, descriptive attribute names, e.g. not using a data- prefix for everything, but I also want to be sure things won't break as new features are added to HTML5. My research so far has not given any clear answers, and suggests that in practice, it's a bit of a wild west.
For example, the W3 HTML5 validator seems to accept made-up attribute names that follow basic conventions like using only a-z and hyphens, but only when they're used on custom elements. It complains about things like using special characters or repeating the same attribute, so that suggests that it's not simply giving up validation completely on a custom element, but actually considers arbitrary attribute names to be valid in that context.
Google's developer resources as a page Custom Element Best Practices, but as far as I can tell it does not answer this question. However, their examples seem to stick to using existing attribute names like checked and disabled. Examples from Google's web component-focused javascript library Lit seem to make use of arbitrary attribute names, however.
My question boils down to:
What, if any, is the official word in the spec on how to name custom attributes for custom elements?
If there's no official word, what is considered to be best practices? How can anyone using custom elements be sure that their attributes will not trigger unexpected functionality in future browsers?
The specification defines the attributes accepted on a custom element as:
Global attributes, except the is attribute
form, for form-associated custom elements — Associates the element with a form element
disabled, for form-associated custom elements — Whether the form control is disabled
readonly, for form-associated custom elements — Affects willValidate, plus any behavior added by the custom element author
name, for form-associated custom elements — Name of the element to use for form submission and in the form.elements API
Any other attribute that has no namespace (see prose).
And then says
Any namespace-less attribute that is relevant to the element's
functioning, as determined by the element's author, may be specified
on an autonomous custom element, so long as the attribute name is
XML-compatible and contains no ASCII upper alphas. The exception is
the is attribute, which must not be specified on an autonomous custom
element (and which will have no effect if it is).
Customized built-in elements follow the normal requirements for
attributes, based on the elements they extend. To add custom
attribute-based behavior, use data-* attributes.
I've been seeing these attributes around on more modern websites like GitHub and such, and they always seemed to coincide with a customized popover like the title attribute.
Option 1
Option 2
Option 3
Option 4
I read some documents about data- attributes on HTML5 Doctor, and I'm not quite sure of the point.
Is there some SEO or accessibility benefit to using them? And what is the plugin(hopefully jQuery) commonly being used to create the popovers in this specific case?
Simply, the specification for custom data attributes states that any attribute that starts with “data-” will be treated as a storage area for private data (private in the sense that the end user can’t see it – it doesn’t affect layout or presentation).
This allows you to write valid HTML markup (passing an HTML 5 validator) while, simultaneously, embedding data within your page. A quick example:
<li class="user" data-name="John Resig" data-city="Boston"
data-lang="js" data-food="Bacon">
<b>John says:</b> <span>Hello, how are you?</span>
</li>
From : Ejohn.org 'Not sure about the external link policy, just putting it in here in case someone wants to know'
HTML5 data-* attribute is used for storing data in element
For manipulating with this attribute you can use jQuery.data() or .data() methods.
The main point is that data- attributes will not clash with attributes that may added to HTML later or with browser-specific attributes. The idea is to give an author a playground, a name space where he can use attributes for private purposes without fear of having them ever interpreted as standard or vendor-defined attributes in some different meaning.
According to this idea, search engines and assistive software ignore such attributes, as they have no interoperable meaning.
The HTML5 spec define how to set custom attributes using data-* prefix,
like:
<div data-attr="somedata"></div>
But what would be the difference if we write just:
<div attr="somedata"></div>
And I actually prefer the second way since it's shorter.
I can access both attributes using the getAttribute() method.
So is that wrong not using data-* prefix? I tested it only on chrome and IE11, so maybe there are other browsers to worry about?
HTML5 defines the data-* attributes as valid, while other custom attributes are not. So what?
If you run your code through an HTML validator it will look for invalid attributes. Among other things, they could indicate a typo. An HTML5 validator will accept data-* attributes but it isn’t psychic. It has no way of judging which other new attributes are part of the plan.
If you create a new attribute, it may not play nicely with future changes in HTML which may coincidentally use the same attribute name for a different purpose. The data-* attributes are exempt from future implementation.
A corollary of the above is that including additional libraries which also make arbitrary changes may interfere with your own code.
JavaScript cooperates with the data-* attributes by automatically collecting them in a dataset property for each element. If you make up another attribute it won’t be included.
If none of the above points are important to you, then, by all means, use whatever attribute names you like. As regards the last point above, you can always access your own arbitrary attributes using JavaScript’s *Attribute functions which will work just well on any attribute, regardless of its validity.
Speaking of JavaScript, there is no concept of HTML validity for JavaScript, and you can use JavaScript to assign any attribute names you like without fear of the HTML validator police knocking at your door. However, you still run the risk of competing with additional libraries or future implementations.
According to many recent HTML specs, when we are using custom attributes (meaning any attributes not defined in the spec), we should prefix them with data-. However, I see no reason to have to do this (unless you require perfectly valid HTML, obviously). Pretty much all current browsers correctly ignore custom attributes, meaning no conflicts except with identically-named attributes from others' code, and we can ignore even this with custom prefixes or something similar (as suggested on the AngularJS directive page). What, if any, other benefits are there? This question has been asked before, at least twice, but both are pretty old.
I forget where I read it, but some guide said custom HTML tags need dashes, and single-word tags aren't valid. First of all, why? Second, should we do this, and why (besides being valid)? Would there be any problem with underscores or camelCase, etc.? Also, conflicts with existing elements shouldn't be a problem, if, like with data attributes, you prefix or suffix them, etc. See the Angular directive page again.
I'm sure all these questions have been asked before, but I'm combining them into one. Is that a good idea (quick, someone ask on Meta)?
The data-* attributes have two advantages:
It is a convention meaning other programmers will understand quickly that it is a custom attribute.
You get a DOM Javascript API for free: HTMLElement.dataset. If you use jQuery, it leverages this to populates the keys and values you find with .data().
The reason for the - in custom element names is for two basic reasons:
It is a quick way for the HTML parser to know it is a custom element instead of a standard element.
You don't run into the issue of a new standard element being added with the same name which would cause conflict if you register a custom Javascript prototype for the DOM element.
Should you use your own custom element name? Right now it is so new that don't expect it to be fully supported. Let's say it does work. You have to balance the issue of the extra complexity with the benefit. If you can get away with a classname, then use a classname. But if you need a whole new element with a custom Javascript DOM prototype for the element, then you may have a valid usage of it.
I am seeing some attribute I have never seen before in a div tag. I haven't touch html for a while but googling the attribute didn't return much useful info.
<div dataquery="#item_1306" comp="box.components.Flashplayer" id="box_Flashplayer_2" propertyquery="#box_Flashplaye_2" class="box_Flashplaye_style2"...
My question is, do you know what are these "dataquery" "comp" and "propertyquery" attributes?
Thanks alot folks.
HTML is often enhanced with custom attributes these days, and HTML5 explicitly allows for that. Normally these attributes should be prefixed with "data-", but obviously this is not the case here.
The meaning depends most probably on a script included in the page.
For example, in twitter bootstrap it is common to see attributes like <body data-spy='scroll'> which is than interpreted by a script and allows for monitoring the amount a user scrolls.
When including Facebook like buttons you may have attributes like data-style which controls whether a box, or a button, or hwatever is used.
You can add you own attributes to elements. I don't think theese atributes are standard attributes lika class and name but an attribute that the programmer has added self for some purpose.
Those are not W3C attributes, they have used to perform some task, may be to the lagulage it used and may performance some special tags, But its not best practice because it gives HTML validation errors, better thing is use data-xxxx tag for extra attributes.
More readings.
http://www.javascriptkit.com/dhtmltutors/customattributes.shtml
http://ejohn.org/blog/html-5-data-attributes/
http://html5doctor.com/html5-custom-data-attributes/