Tag: attributes

Did You Know the Ordered List Element Has Start and Reversed Attributes?

I sure didn’t! Tomek Sułkowsi shows how we can reverse the numbering of ordered lists with a simple HTML attribute:

<ol reversed>   <li>Apple</li>   <li>Banana</li>   <li>Pear</li> </ol>

And the start attribute can be added to begin the list at a number other than one, like this:

<ol start="2">   <li>Apple</li>   <li>Banana</li>   <li>Pear</li> </ol>

I’m not sure how I never knew about these properties! I guess I can see how they might come in handy in the future. There are plenty of times when we need to break up ordered lists here on CSS-Tricks with things like code blocks and having a way to pick a list back up where it left off is a nice convenience.

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A Complete Guide to Data Attributes

Introduction

HTML elements can have attributes on them that are used for anything from accessibility information to stylistic control.

<!-- We can use the `class` for styling in CSS, and we've also make this into a landmark region --> <div class="names" role="region" aria-label="Names"></div>

What is discouraged is making up your own attributes, or repurposing existing attributes for unrelated functionality.

<!-- `highlight` is not an HTML attribute --> <div highlight="true"></div>  <!-- `large` is not a valid value of `width` --> <div width="large">

There are a variety of reasons this is bad. Your HTML becomes invalid, which may not have any actual negative consequences, but robs you of that warm fuzzy valid HTML feeling. The most compelling reason is that HTML is a living language and just because attributes and values that don’t do anything today doesn’t mean they never will.

Good news though: you can make up your own attributes. You just need to prefix them with data-* and then you’re free to do what you please!

Syntax

It can be awfully handy to be able to make up your own HTML attributes and put your own information inside them. Fortunately, you can! That’s exactly what data attributes are. They are like this:

<!-- They don't need a value --> <div data-foo></div>  <!-- ...but they can have a value --> <div data-size="large"></div>  <!-- You're in HTML here, so careful to escape code if you need to do something like put more HTML inside --> <li data-prefix="Careful with HTML in here."><li>  <!-- You can keep dashing if you like --> <aside data-some-long-attribute-name><aside>

Data attributes are often referred to as data-* attributes, as they are always formatted like that. The word data, then a dash -, then other text you can make up.

Can you use the data attribute alone?

<div data=""></div>

It’s probably not going to hurt anything, but you won’t get the JavaScript API we’ll cover later in this guide. You’re essentially making up an attribute for yourself, which as I mentioned in the intro, is discouraged.

What not to do with data attributes

Store content that should be accessible. If the content should be seen or read on a page, don’t only put them in data attributes, but make sure that content is in the HTML content somewhere.

<!-- This isn't accessible content --> <div data-name="Chris Coyier"></div>  <!-- If you need programmatic access to it but shouldn't be seen, there are other ways... --> <div>   <span class="visually-hidden">Chris Coyier</span> </div>

Here’s more about hiding things.

Styling with data attributes

CSS can select HTML elements based on attributes and their values.

/* Select any element with this data attribute and value */ [data-size="large"] {   padding: 2rem;   font-size: 125%; }  /* You can scope it to an element or class or anything else */ button[data-type="download"] { } .card[data-pad="extra"] { }

This can be compelling. The predominant styling hooks in HTML/CSS are classes, and while classes are great (they have medium specificity and nice JavaScript methods via classList) an element either has it or it doesn’t (essentially on or off). With data-* attributes, you get that on/off ability plus the ability to select based on the value it has at the same specificity level.

/* Selects if the attribute is present at all */ [data-size] { }  /* Selects if the attribute has a particular value */ [data-state="open"], [aria-expanded="true"] { }  /* "Starts with" selector, meaning this would match "3" or anything starting with 3, like "3.14" */ [data-version^="3"] { }  /* "Contains" meaning if the value has the string anywhere inside it */ [data-company*="google"] { }

The specificity of attribute selectors

It’s the exact same as a class. We often think of specificity as a four-part value:

inline style, IDs, classes/attributes, tags

So a single attribute selector alone is 0, 0, 1, 0. A selector like this:

div.card[data-foo="bar"] { }

…would be 0, 0, 2, 1. The 2 is because there is one class (.card) and one attribute ([data-foo="bar"]), and the 1 is because there is one tag (div).

Attribute selectors have less specificity than an ID, more than an element/tag, and the same as a class.

Case-insensitive attribute values

In case you’re needing to correct for possible capitalization inconsistencies in your data attributes, the attribute selector has a case-insensitive variant for that.

/* Will match <div data-state="open"></div> <div data-state="Open"></div> <div data-state="OPEN"></div> <div data-state="oPeN"></div> */ [data-state="open" i] { }

It’s the little i within the bracketed selector.

Using data attributes visually

CSS allows you to yank out the data attribute value and display it if you need to.

/* <div data-emoji="✅"> */  [data-emoji]::before {   content: attr(data-emoji); /* Returns '✅' */   margin-right: 5px; }

Example styling use-case

You could use data attributes to specify how many columns you want a grid container to have.

<div data-columns="2"></div> <div data-columns="3"></div> <div data-columns="4"></div>

Accessing data attributes in JavaScript

Like any other attribute, you can access the value with the generic method getAttribute.

let value = el.getAttribute("data-state");  // You can set the value as well. // Returns data-state="collapsed" el.setAttribute("data-state", "collapsed");

But data attributes have their own special API as well. Say you have an element with multiple data attributes (which is totally fine):

<span    data-info="123"    data-index="2"    data-prefix="Dr. "   data-emoji-icon="🏌️‍♀️" ></span>

If you have a reference to that element, you can set and get the attributes like:

// Get span.dataset.info; // 123 span.dataset.index; // 2  // Set span.dataset.prefix = "Mr. "; span.dataset.emojiIcon = "🎪";

Note the camelCase usage on the last line there. It automatically converts kebab-style attributes in HTML, like data-this-little-piggy, to camelCase style in JavaScript, like dataThisLittlePiggy.

This API is arguably not quite as nice as classList with the clear add, remove, toggle, and replace methods, but it’s better than nothing.

You have access to inline datasets as well:

<img src="spaceship.png"   data-ship-id="324" data-shields="72%"   onclick="pewpew(this.dataset.shipId)"> </img>

JSON data inside data attributes

<ul>   <li data-person='     {       "name": "Chris Coyier",       "job": "Web Person"     }   '></li> </ul>

Hey, why not? It’s just a string and it’s possible to format it as valid JSON (mind the quotes and such). You can yank that data and parse it as needed.

const el = document.querySelector("li");  let json = el.dataset.person; let data = JSON.parse(json);  console.log(data.name); // Chris Coyier console.log(data.job); // Web Person

JavaScript use-cases

The concept is that you can use data attributes to put information in HTML that JavaScript may need access to do certain things.

A common one would have to do with database functionality. Say you have a “Like” button:

<button data-id="435432343">♡</button>

That button could have a click handler on it which performs an Ajax request to the server to increment the number of likes in a database on click. It knows which record to update because it gets it from the data attribute.

Specifications

Browser support

This browser support data is from Caniuse, which has more detail. A number indicates that browser supports the feature at that version and up.

Desktop

Chrome Firefox IE Edge Safari
7 6 11 12 5.1

Mobile / Tablet

Android Chrome Android Firefox Android iOS Safari
79 68 3 5.0-5.1

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What’s the Difference Between Width/Height in CSS and Width/Height HTML attributes?

Some HTML elements accept width and height as attributes. Some do not. For example:

<!-- valid, works, is a good idea --> <img width="500" height="400" src="..." alt="..."> <iframe width="600" height="400" src="..."></iframe> <svg width="20" height="20"></svg>  <!-- not valid, doesn't work, not a good idea --> <div width="40" height="40"></div> <span width="100" height="10"></span>

Those attributes are sometimes referred to as presentational attributes. The thing to know about them is that they are overridden by any other styling information whatsoever. That makes them ideal as a fallback.

So, if CSS loads and has a declaration like:

img {   width: 400px; }

…that is going to override the width="500" on the <img> tag above. Presentational attributes are the weakest kind of styling, so they are overridden by any CSS, even selectors with very low specificity.

What might be a smidge confusing is that presentational attributes seem like they would have high specificity. These inline styles, for instance, are very strong:

<img style="width: 500px; height: 400px;" src="..." alt="...">

Using an inline style (which works on any element, not a select few), we’ve moved from the weakest way to apply width and height to one of the strongest. Regular CSS will not override this, with a selector of any specificity strength. If we need to override them from CSS, we’ll need !important rules.

img {   width: 400px !important; }

To reiterate, presentational attributes on elements that accept them (e.g. <img>, <iframe>, <canvas>, <svg>, <video>) are a good idea. They are fallback sizing and sizing information as the page is loading. They are particularly useful on <svg>, which may size themselves enormously in an awkward way if they have a viewBox and lack width and height attributes. Browsers even do special magic with images, where the width and height are used to reserve the correct aspect-ratio derived space in a situation with fluid images, which is great for a smooth page loading experience.

But presentational attributes are also weak and are usually overridden in the CSS.

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