You can have multiple classes on an HTML element:

Nothing incorrect or invalid there at all. It has two classes. In CSS, both of these will apply:

.module { }
.p-2 { }
const div = document.querySelector("div");
console.log(div.classList.contains("module")); // true
console.log(div.classList.contains("p-3")); // false

But what about grouping them? All we have here is a space-separated string. Maybe that’s fine. But maybe we can make things more clear!

Years ago, Harry Roberts talked about grouping them. He wrapped groups of classes in square brackets:

<div class="[ foo foo--bar ] [ baz baz--foo ]">

The example class names above are totally abstract just to demonstrate the grouping. Imagine they are like primary names and variations as one group, then utility classes as another group:

<header class="[ site-header site-header-large ] [ mb-10 p-15 ]">

Those square brackets? Meaningless. Those are there to visually represent the groups to us developers. Technically, they are also classes, so if some sadist wrote .[ {}, it would do stuff in your CSS. But that’s so unlikely that, hopefully, the clarity from the groups outweighs it and is more helpful.

That example above groups the primary name and a variation in one group and some example utility classes in another group.

I’m not necessarily recommending that approach. They are simply groups of classes that you might have.

Here’s the same style of grouping, with different groups:

<button class="[ link-button ] [ font-base text-xs color-primary ] [ js-trigger ]" type="button" hidden>

That example has a single primary name, utility classes with different naming styles, and a third group for JavaScript specific selectors.

Harry wound up shunning this approach a few years ago, saying that the look of it was just too weird for the variety of people and teams he worked with. It caused enough confusion that the benefits of grouped classes weren’t worth it. He suggested line breaks instead:

<div class="media media--large testimonial testimonial--main"> 

That seems similarly clear to me. The line breaks in HTML are totally fine. Plus, the browser will have no trouble with that and JSX is generally written with lots of line breaks in HTML anyway because of how much extra stuff is plopped onto elements in there, like event handlers and props.

Perhaps we combine the ideas of line breaks as separators and identified groups… with emojis!

See the Pen
Grouping Classes
by Chris Coyier (@chriscoyier)
on CodePen.

Weird, but fun. Emojis are totally valid there. Like the square brackets, they could also do things if someone wrote a class name for them, but that’s generally unlikely and something for a team to talk about.

Another thing I’ve seen used is data-* attributes for groups instead of classes, like…

<div class="primary-name" data-js="js-hook-1 js-hook-2" data-utilities="padding-large"
>

You can still select and style based on attributes in both CSS and JavaScript, so it’s functional, though slightly less convenient because of the awkward selectors like [data-js="js-hook-1"] and lack of convenient APIs like classList.

How about you? Do you have any other clever ideas for class name groups?

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