data attributes – CSS-Tricks https://css-tricks.com Tips, Tricks, and Techniques on using Cascading Style Sheets. Thu, 13 Jun 2024 17:18:50 +0000 en-US hourly 1 https://wordpress.org/?v=6.5.5 https://i0.wp.com/css-tricks.com/wp-content/uploads/2021/07/star.png?fit=32%2C32&ssl=1 data attributes – CSS-Tricks https://css-tricks.com 32 32 45537868 Don’t Fight the Cascade, Control It! https://css-tricks.com/dont-fight-the-cascade-control-it/ https://css-tricks.com/dont-fight-the-cascade-control-it/#comments Mon, 10 Jan 2022 15:22:08 +0000 https://css-tricks.com/?p=359886 If you’re disciplined and make use of the inheritance that the CSS cascade provides, you’ll end up writing less CSS. But because our styles often comes from all kinds of sources — and can be a pain to structure and …


Don’t Fight the Cascade, Control It! originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

]]>
If you’re disciplined and make use of the inheritance that the CSS cascade provides, you’ll end up writing less CSS. But because our styles often comes from all kinds of sources — and can be a pain to structure and maintain—the cascade can be a source of frustration, and the reason we end up with more CSS than necessary.

Some years ago, Harry Roberts came up with ITCSS and it’s a clever way of structuring CSS.

Mixed with BEM, ITCSS has become a popular way that people write and organize CSS.

However, even with ITCSS and BEM, there are still times where we still struggle with the cascade. For example, I’m sure you’ve had to @import external CSS components at a specific location to prevent breaking things, or reach for the dreaded !important at some point in time.

Recently, some new tools were added to our CSS toolbox, and they allow us to finally control the cascade. Let’s look at them.

O cascade, :where art thou?

Using the :where pseudo-selector allows us to remove specificity to “just after the user-agent default styles,” no matter where or when the CSS is loaded into the document. That means the specificity of the whole thing is literally zero — totally wiped out. This is handy for generic components, which we’ll look into in a moment.

First, imagine some generic <table> styles, using :where:

:where(table) {
  background-color: tan;
}

Now, if you add some other table styles before the :where selector, like this:

table {
  background-color: hotpink;
}

:where(table) {
  background-color: tan;
}

…the table background becomes hotpink, even though the table selector is specified before the :where selector in the cascade. That’s the beauty of :where, and why it’s already being used for CSS resets.

:where has a sibling, which has almost the exact opposite effect: the :is selector.

The specificity of the :is() pseudo-class is replaced by the specificity of its most specific argument. Thus, a selector written with :is() does not necessarily have equivalent specificity to the equivalent selector written without :is(). Selectors Level 4 specification

Expanding on our previous example:

:is(table) {
  --tbl-bgc: orange;
}
table {
  --tbl-bgc: tan;
}
:where(table) {
  --tbl-bgc: hotpink;
  background-color: var(--tbl-bgc);
}

The <table class="c-tbl"> background color will be tan because the specificity of :is is the same as table, but table is placed after.

However, if we were to change it to this:

:is(table, .c-tbl) {
  --tbl-bgc: orange;
}

…the background color will be orange, since :is has the weight of it’s heaviest selector, which is .c-tbl.

Example: A configurable table component

Now, let’s see how we can use :where in our components. We’ll be building a table component, starting with the HTML:

Let’s wrap .c-tbl in a :where-selector and, just for fun, add rounded corners to the table. That means we need border-collapse: separate, as we can’t use border-radius on table cells when the table is using border-collapse: collapse:

:where(.c-tbl) {
  border-collapse: separate;
  border-spacing: 0;
  table-layout: auto;
  width: 99.9%;
}

The cells use different styling for the <thead> and <tbody>-cells:

:where(.c-tbl thead th) {
  background-color: hsl(200, 60%, 40%);
  border-style: solid;
  border-block-start-width: 0;
  border-inline-end-width: 1px;
  border-block-end-width: 0;
  border-inline-start-width: 0;
  color: hsl(200, 60%, 99%);
  padding-block: 1.25ch;
  padding-inline: 2ch;
  text-transform: uppercase;
}
:where(.c-tbl tbody td) {
  background-color: #FFF;
  border-color: hsl(200, 60%, 80%);
  border-style: solid;
  border-block-start-width: 0;
  border-inline-end-width: 1px;
  border-block-end-width: 1px;
  border-inline-start-width: 0;
  padding-block: 1.25ch;
  padding-inline: 2ch;
}

And, because of our rounded corners and the missing border-collapse: collapse, we need to add some extra styles, specifically for the table borders and a hover state on the cells:

:where(.c-tbl tr td:first-of-type) {
  border-inline-start-width: 1px;
}
:where(.c-tbl tr th:last-of-type) {
  border-inline-color: hsl(200, 60%, 40%);
}
:where(.c-tbl tr th:first-of-type) {
  border-inline-start-color: hsl(200, 60%, 40%);
}
:where(.c-tbl thead th:first-of-type) {
  border-start-start-radius: 0.5rem;
}
:where(.c-tbl thead th:last-of-type) {
  border-start-end-radius: 0.5rem;
}
:where(.c-tbl tbody tr:last-of-type td:first-of-type) {
  border-end-start-radius: 0.5rem;
}
:where(.c-tbl tr:last-of-type td:last-of-type) {
  border-end-end-radius: 0.5rem;
}
/* hover */
@media (hover: hover) {
  :where(.c-tbl) tr:hover td {
    background-color: hsl(200, 60%, 95%);
  }
}

Now we can create variations of our table component by injecting other styles before or after our generic styles (courtesy of the specificity-stripping powers of :where), either by overwriting the .c-tbl element or by adding a BEM-style modifier-class (e.g. c-tbl--purple):

<table class="c-tbl c-tbl--purple">
.c-tbl--purple th {
  background-color: hsl(330, 50%, 40%)
}
.c-tbl--purple td {
  border-color: hsl(330, 40%, 80%);
}
.c-tbl--purple tr th:last-of-type {
  border-inline-color: hsl(330, 50%, 40%);
}
.c-tbl--purple tr th:first-of-type {
  border-inline-start-color: hsl(330, 50%, 40%);
}

Cool! But notice how we keep repeating colors? And what if we want to change the border-radius or the border-width? That would end up with a lot of repeated CSS.

Let’s move all of these to CSS custom properties and, while we’re at it, we can move all configurable properties to the top of the component’s “scope“ — which is the table element itself — so we can easily play around with them later.

CSS Custom Properties

I’m going to switch things up in the HTML and use a data-component attribute on the table element that can be targeted for styling.

<table data-component="table" id="table">

That data-component will hold the generic styles that we can use on any instance of the component, i.e. the styles the table needs no matter what color variation we apply. The styles for a specific table component instance will be contained in a regular class, using custom properties from the generic component.

[data-component="table"] {
  /* Styles needed for all table variations */
}
.c-tbl--purple {
  /* Styles for the purple variation */
}

If we place all the generic styles in a data-attribute, we can use whatever naming convention we want. This way, we don’t have to worry if your boss insists on naming the table’s classes something like .BIGCORP__TABLE, .table-component or something else.

In the generic component, each CSS property points to a custom property. Properties, that have to work on child-elements, like border-color, are specified at the root of the generic component:

:where([data-component="table"]) {
  /* These will will be used multiple times, and in other selectors */
  --tbl-hue: 200;
  --tbl-sat: 50%;
  --tbl-bdc: hsl(var(--tbl-hue), var(--tbl-sat), 80%);
}

/* Here, it's used on a child-node: */
:where([data-component="table"] td) {
  border-color: var(--tbl-bdc);
}

For other properties, decide whether it should have a static value, or be configurable with its own custom property. If you’re using custom properties, remember to define a default value that the table can fall back to in the event that a variation class is missing.

:where([data-component="table"]) {
  /* These are optional, with fallbacks */
  background-color: var(--tbl-bgc, transparent);
  border-collapse: var(--tbl-bdcl, separate);
}

If you’re wondering how I’m naming the custom properties, I’m using a component-prefix (e.g. --tbl) followed by an Emmett-abbreviation (e.g. -bgc). In this case, --tbl is the component-prefix, -bgc is the background color, and -bdcl is the border collapse. So, for example, --tbl-bgc is the table component’s background color. I only use this naming convention when working with component properties, as opposed to global properties which I tend to keep more general.

Now, if we open up DevTools, we can play around with the custom properties. For example, We can change --tbl-hue to a different hue value in the HSL color, set --tbl-bdrs: 0 to remove border-radius, and so on.

A :where CSS rule set showing the custom properties of the table showing how the cascade’s specificity scan be used in context.

When working with your own components, this is the point in time you’ll discover which parameters (i.e. the custom property values) the component needs to make things look just right.

We can also use custom properties to control column alignment and width:

:where[data-component="table"] tr > *:nth-of-type(1)) {
  text-align: var(--ca1, initial);
  width: var(--cw1, initial);
  /* repeat for column 2 and 3, or use a SCSS-loop ... */
}

In DevTools, select the table and add these to the element.styles selector:

element.style {
  --ca2: center; /* Align second column center */
  --ca3: right; /* Align third column right */
}

Now, let’s create our specific component styles, using a regular class, .c-tbl (which stands for “component-table” in BEM parlance). Let’s toss that class in the table markup.

<table class="c-tbl" data-component="table" id="table">

Now, let’s change the --tbl-hue value in the CSS just to see how this works before we start messing around with all of the property values:

.c-tbl {
  --tbl-hue: 330;
}

Notice, that we only need to update properties rather than writing entirely new CSS! Changing one little property updates the table’s color — no new classes or overriding properties lower in the cascade.

Notice how the border colors change as well. That’s because all the colors in the table inherit from the --tbl-hue variable

We can write a more complex selector, but still update a single property, to get something like zebra-striping:

.c-tbl tr:nth-child(even) td {
  --tbl-td-bgc: hsl(var(--tbl-hue), var(--tbl-sat), 95%);
}

And remember: It doesn’t matter where you load the class. Because our generic styles are using :where, the specificity is wiped out, and any custom styles for a specific variation will be applied no matter where they are used. That’s the beauty of using :where to take control of the cascade!

And best of all, we can create all kinds of table components from the generic styles with a few lines of CSS.

Purple table with zebra-striped columns
Light table with a “noinlineborder” parameter… which we’ll cover next

Adding parameters with another data-attribute

So far, so good! The generic table component is very simple. But what if it requires something more akin to real parameters? Perhaps for things like:

  • zebra-striped rows and columns
  • a sticky header and sticky column
  • hover-state options, such as hover row, hover cell, hover column

We could simply add BEM-style modifier classes, but we can actually accomplish it more efficiently by adding another data-attribute to the mix. Perhaps a data-param that holds the parameters like this:

<table data-component="table" data-param="zebrarow stickyrow">

Then, in our CSS, we can use an attribute-selector to match a whole word in a list of parameters. For example, zebra-striped rows:

[data-component="table"][data-param~="zebrarow"] tr:nth-child(even) td {
  --tbl-td-bgc: var(--tbl-zebra-bgc);
}

Or zebra-striping columns:

[data-component="table"][data-param~="zebracol"] td:nth-of-type(odd) {
  --tbl-td-bgc: var(--tbl-zebra-bgc);
}

Let’s go nuts and make both the table header and the first column sticky:


[data-component="table"][data-param~="stickycol"] thead tr th:first-child,[data-component="table"][data-param~="stickycol"] tbody tr td:first-child {
  --tbl-td-bgc: var(--tbl-zebra-bgc);
  inset-inline-start: 0;
  position: sticky;
}
[data-component="table"][data-param~="stickyrow"] thead th {
  inset-block-start: -1px;
  position: sticky;
}

Here’s a demo that allows you to change one parameter at a time:

The default light theme in the demo is this:

.c-tbl--light {
  --tbl-bdrs: 0;
  --tbl-sat: 15%;
  --tbl-th-bgc: #eee;
  --tbl-th-bdc: #eee;
  --tbl-th-c: #555;
  --tbl-th-tt: normal;
}

…where data-param is set to noinlineborder which corresponds to these styles:

[data-param~="noinlineborder"] thead tr > th {
  border-block-start-width: 0;
  border-inline-end-width: 0;
  border-block-end-width: var(--tbl-bdw);
  border-inline-start-width: 0;
}

I know my data-attribute way of styling and configuring generic components is very opinionated. That’s just how I roll, so please feel free to stick with whatever method you’re most comfortable working with, whether it’s a BEM modifier class or something else.

The bottom line is this: embrace :where and :is and the cascade-controlling powers they provide. And, if possible, construct the CSS in such a way that you wind up writing as little new CSS as possible when creating new component variations!

Cascade Layers

The last cascade-busting tool I want to look at is “Cascade Layers.” At the time of this writing, it’s an experimental feature defined in the CSS Cascading and Inheritance Level 5 specification that you can access in Safari or Chrome by enabling the #enable-cascade-layers flag.

Bramus Van Damme sums up the concept nicely:

The true power of Cascade Layers comes from its unique position in the Cascade: before Selector Specificity and Order Of Appearance. Because of that we don’t need to worry about the Selector Specificity of the CSS that is used in other Layers, nor about the order in which we load CSS into these Layers — something that will come in very handy for larger teams or when loading in third-party CSS.

Perhaps even nicer is his illustration showing where Cascade Layers fall in the cascade:

Credit: Bramus Van Damme

At the beginning of this article, I mentioned ITCSS — a way of taming the cascade by specifying the load-order of generic styles, components etc. Cascade Layers allow us to inject a stylesheet at a given location. So a simplified version of this structure in Cascade Layers looks like this:

@layer generic, components;

With this single line, we’ve decided the order of our layers. First come the generic styles, followed by the component-specific ones.

Let’s pretend that we’re loading our generic styles somewhere much later than our component styles:

@layer components {
  body {
    background-color: lightseagreen;
  }
}

/* MUCH, much later... */

@layer generic { 
  body {
    background-color: tomato;
  }
}

The background-color will be lightseagreen because our component styles layer is set after the generic styles layer. So, the styles in the components layer “win” even if they are written before the generic layer styles.

Again, just another tool for controlling how the CSS cascade applies styles, allowing us more flexibility to organize things logically rather than wrestling with specificity.

Now you’re in control!

The whole point here is that the CSS cascade is becoming a lot easier to wrangle, thanks to new features. We saw how the :where and :is pseudo-selectors allows us to control specificity, either by stripping out the specificity of an entire ruleset or taking on the specificity of the most specific argument, respectively. Then we used CSS Custom Properties to override styles without writing a new class to override another. From there, we took a slight detour down data-attribute lane to help us add more flexibility to create component variations merely by adding arguments to the HTML. And, finally, we poked at Cascade Layers which should prove handy for specifying the loading order or styles using @layer.

If you leave with only one takeaway from this article, I hope it’s that the CSS cascade is no longer the enemy it’s often made to be. We are gaining the tools to stop fighting it and start leaning into even more.


Header photo by Stephen Leonardi on Unsplash


Don’t Fight the Cascade, Control It! originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

]]>
https://css-tricks.com/dont-fight-the-cascade-control-it/feed/ 4 359886
A Complete Guide to Data Attributes https://css-tricks.com/a-complete-guide-to-data-attributes/ https://css-tricks.com/a-complete-guide-to-data-attributes/#comments Tue, 18 Feb 2020 00:07:24 +0000 https://css-tricks.com/?p=302917 Everything you ever wanted to know about data attributes in HTML, CSS, and JavaScript.


A Complete Guide to Data Attributes originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

]]>

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).

Illustration of a CSS selector including a data attribute.

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

ChromeFirefoxIEEdgeSafari
7611125.1

Mobile / Tablet

Android ChromeAndroid FirefoxAndroidiOS Safari
12612735.0-5.1

A Complete Guide to Data Attributes originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

]]>
https://css-tricks.com/a-complete-guide-to-data-attributes/feed/ 19 302917
Working with Attributes on DOM Elements https://css-tricks.com/working-with-attributes-on-dom-elements/ https://css-tricks.com/working-with-attributes-on-dom-elements/#comments Fri, 30 Aug 2019 14:30:43 +0000 https://css-tricks.com/?p=294650 The DOM is just a little weird about some things, and the way you deal with attributes is no exception. There are a number of ways to deal with the attributes on elements. By attributes, I mean things like the …


Working with Attributes on DOM Elements originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

]]>
The DOM is just a little weird about some things, and the way you deal with attributes is no exception. There are a number of ways to deal with the attributes on elements. By attributes, I mean things like the id in <div id="cool"></div>. Sometimes you need to set them. Sometimes you need to get them. Sometimes there are fancy helper APIs. Sometimes there isn’t.

For this article, I’ll assume el is a DOM element in your JavaScript. Let’s say you’ve done something like const el = document.querySelector("#cool"); and matched <div id="cool"> or whatever.

Some attributes are also attributes of the DOM object itself, so iff you need to set an id or title, you can do:

el.id; // "cool"
el.title = "my title";
el.title; // "my title";

Others that work like that are lang, align, and all the big events, like onclick.

Then there are attributes that work similarly to that but are nested deeper. The style attribute is like that. If you log el.style you’ll see a ton of CSS style declarations. You can get and set them easily:

el.style.color = "red";
module.style.backgroundColor = "black";

You can get computed colors this way too. If you do module.style.color hoping to get the color of an element out of the gate, you probably won’t get it. For that, you’d have to do:

let style = window.getComputedStyle(el);
style.color; // whatever in CSS won out

But not all attributes are like first-class attributes like that.

el['aria-hidden'] = true; // nope

That “works” in that it sets that as a property, but it doesn’t set it in the DOM the proper way. Instead, you’ll have to use the generic setter and getter functions that work for all attributes, like:

el.setAttribute("aria-hidden", true);
el.getAttribute("aria-hidden");

Some attributes have fancy helpers. The most fancy is classList for class attributes. On an element like:

<div class="module big"></div>

You’d have:

el.classList.value; // "module big"
el.classList.length; // 2
el.classList.add("cool"); // adds the class "cool", so "module big cool"
el.classList.remove("big"); // removes "big", so "module cool"
el.classList.toggle("big"); // adds "big" back, because it was missing (goes back and forth)
el.classList.contains("module"); // true

There’s even more, and classList itself behaves like an array so you can forEach it and such. That’s a pretty strong reason to use classes, as the DOM API around them is so handy.

Another attribute type that has a somewhat fancy help is data-*. Say you’ve got:

<div data-active="true" data-placement="top right" data-extra-words="hi">test</div> 

You’ve got dataset:

el.dataset;
/*
{
  active: "true",
  "placement", "top right"
*/

el.dataset.active; // "true"
el.dataset.extraWords; // "hi", note the conversion to camelCase

el.dataset.active = "false"; // setters work like this

Working with Attributes on DOM Elements originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

]]>
https://css-tricks.com/working-with-attributes-on-dom-elements/feed/ 8 294650
Styling Based on Scroll Position https://css-tricks.com/styling-based-on-scroll-position/ https://css-tricks.com/styling-based-on-scroll-position/#comments Thu, 07 Mar 2019 15:26:59 +0000 http://css-tricks.com/?p=283200 Rik Schennink documents a system for being able to write CSS selectors that style a page when it has scrolled to a certain point. If you’re like me, you’re already on the lookout for document.addEventListener('scroll' ... and being terrified about …


Styling Based on Scroll Position originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

]]>
Rik Schennink documents a system for being able to write CSS selectors that style a page when it has scrolled to a certain point. If you’re like me, you’re already on the lookout for document.addEventListener('scroll' ... and being terrified about performance. Rik gets to that right away by both debouncing the function as well as marking the event as passive.

The end result is a data-scroll attribute on the <html> element that can be used in the CSS. Meaning if you’re scrolled to 640px down the page, you have <html data-scroll="640"> and could write a selector like:

html:not([data-scroll='0']) {
  padding-top: 3em;
}
html:not([data-scroll='0']) header {
  position: fixed;
}

See the Pen
Writing Dumb JS 🧟‍♂️ and Smart CSS 👩‍🔬
by Rik Schennink (@rikschennink)
on CodePen.

Unfortunately, we don’t have greater than (>) less than (<) selectors in CSS for things like numbered attributes, so the CSS styling potential is fairly limited here. You might ultimately need to update the JavaScript function such that it applies other classes or data attributes based on your math. But you’ll already be set up for good performance here.

“Apply styles when the user has scrolled away from the top” is a legit use case. It makes me think of a once function (like we have in jQuery) where any scroll event would only be triggered once and then not again. They scrolled! So, by definition, they aren’t at the top anymore! But that doesn’t deal with when they scroll back to the top.

I find it generally more useful to use IntersectionObserver for styling things based on scroll position. With it, you can do things like, “has this element been scrolled into view or beyond,” which is generically useful and can be used for scrolled-away-from-top stuff too.

Here’s an example that adds or removes a class if a user has scrolled past a hidden pixel positioned at 500px down the page.

See the Pen
Fixed Header with IntersectionObserver
by Chris Coyier (@chriscoyier)
on CodePen.

That’s performant as well, avoiding any scroll event handlers at all.

And speaking of IntersectionObserver, check out “Trust is Good, Observation is Better—Intersection Observer v2”.


Styling Based on Scroll Position originally published on CSS-Tricks, which is part of the DigitalOcean family. You should get the newsletter.

]]>
https://css-tricks.com/styling-based-on-scroll-position/feed/ 11 283200