[err4nt]

> None of the modifications done through the dataset api would reflect in the DOM and be readable by CSS unless you were to convert the list to a space separated string and explicitly set the attribute.

I'm really not sure what you mean by this. If you set the data attribute any of these ways, it can be targeted in CSS with [data-demo="example"]:

    el.dataset.demo = 'example'
    el.dataset['demo'] = 'example'
    el.setAttribute('demo', 'example')

CSS doesn't require a space separated anything. When you use an attribute selector in CSS it treats the entire value as a string, spaces included. But it's not classes versus attribute selectors, as class is an attribute, and therefore also something you can select with attribute selectors.

Also, think about the asymmetry between CSS and HTML when considering saving characters, one CSS selector targets ∞ tags, so I'd rather write slightly longer selector one time, than need to use a much longer 'namespaced' value on each element where I want the style to apply. That's leveraging what CSS does best!

[criswell]

I'm just saying if you want to target something on an element it needs to be set in an attribute and classList takes care of this.

I use classes strictly for styling. I change these styles by adding and removing class names and classList handles it very well without me needing to read the data attribute, make it an array, manipulate it, join it and update the attribute.

[err4nt]

I feel like you're still thinking small in terms of attributes, and big in terms of values. Many many values all crammed into one attribute (class), but the reality is you can invent infinite (∞) data attributes. There's literally no need for you to format the values as a list of space-separated values…unless you want to. But if you don't want to, there's no need. Consider this, instead of targeting something with classes like this .active.demo, and setting it like this

    el.classList.add('active')
    el.classList.add('demo')

You would NOT need to do something like this to use data attributes, [data-example~=active][data-example~=demo] and to set it like this:

    if (!el.dataset.example.split(' ').includes('demo')) {
      el.dataset.example += ' demo'
    }

You could instead easily set two attributes and test for their presence, even if they don't have values (or you're not using them)

    el.dataset.active = el.dataset.demo = true

And then you can target that in CSS with [data-active][data-demo]. To remove them later is just as simple:

    el.dataset.active = false

And it's gone! Try to think BIG in terms of attributes, and small in terms of values. It's a lot nicer than trying to cram all of your values into just one attribute when you literally have infinite attributes available to work with!

Not only do you have infinite attributes to work with, but you can

Using classes as your only way to target styles, and ignoring the other aspects of how CSS selectors can target elements is like picking up a guitar and trying to play a song, but only plucking one string. You might be making it harder on yourself to get the job done, and the result isn't any better for the effort.

EDIT: Just for kicks, have you ever considered the flexibility of what data types you can set as an attribute value other than a space separated list of strings? Try this:

    // set JSON to attribute value
    document.documentElement.dataset.example = JSON.stringify({one: 1, two: 2})

    // get JSON from attribute value
    JSON.parse(document.documentElement.dataset.example)

You can even stick a bit of JSON there as the attribute value, which can be parse/stringified by JS, is _easy_ to add or remove properties from and work with on the JS side (not requiring helper methods like classList), and is _still_ targetable by CSS once set on an element :D The possibilities are endless, the apparent limitations a lot of people butt up against are self-imposed.

[criswell]

I'm sorry I'm just not seeing the value in it. I'm just seeing more complexity JS and CSS wise without solving any problems.