Prop For That

Announcing Prop For That, a JS library that backfills what CSS doesn't provide us yet (and maybe never will).

I'm done waiting for CSS to catch up to all the valuable information JS knows and done watching folks write the same little JS to just write a custom property to a component.

demo · docs · npm

Here's a basic example taking the value from a range slider to draw a nice gradient that fills up the slider:

import 'prop-for-that/auto'
// or import 'https://esm.sh/prop-for-that/auto'

<input type="range" data-props-for="range" min="0" max="100" value="40" />

input[type="range"] {
 background: linear-gradient(
 to right in oklab,
 var(--theme) calc(var(--live-value-pct) * 100%),
 var(--track) 0
 );
}

codepen · docs example · codepen collection

Why? #

It's super common to need a few lines of JS for a simple thing like:

• the value of the color input

• the mouse pointer position

• the size of the scrollbar

• the colors present in an image or video

• the battery level

• an element's visibility

• etc

With Prop For That, you just declaratively specify on any element the props you want, and live props show up.

There's an imperitive API too, but the data attribute path is the slickest

Everything is a plugin that loads only if you need it too, ultimately putting you right where you wanted to be: creating something sick in CSS using dynamic information without wiring up some dorky JS.

What kind of props? #

My talk at CSS Day was an enumeration of all the ways CSS can adapt to users, contexts, pages, etc… which made me hyper aware of all the ways CSS couldn't adapt without JS.

Here's a flat list of all the live props currently supported by the library:

1. Pointer x/y in the window

2. Pointer x/y inside/local to an element

3. Viewport pixel height/width values

4. Visual viewport information

5. Element size information

6. Element visibility

7. Scrollbar and thin scrollbar sizes

8. Input element values

9. Input element dirty, touched, pristine, etc

10. Select element value, index, count, etc

11. Colors from an image or gradient (average, accent, light, dark, etc)

12. Colors occuring in a video

13. Video progress

14. Image loaded or broken + natural h/w

15. Clock time

16. FPS

17. Online/offline status

18. Page focused/visible

19. Scroll velocity

20. Accelerometer and device tilt/orientation

21. Geolocation

22. DPR, CPU cores, memory

23. Page navigation type (reload, back, etc)

And a few Chromium only props:

1. Network status like type, speed, save data, etc

2. Battery status

3. CPU pressure

Style Queries #

Style Queries being in all major browsers marks an important milestone for CSS, and made this library much more viable.

Container style queries

Baseline2026newly available

Using Prop For That with Style Queries looks like this:

import 'https://esm.sh/prop-for-that/auto'

<form data-props-for="form-state">
 <input name="name" required>
 <input name="email" type="email" required>
 <button type="submit">Save</button>
</form>

@container style(--live-all-valid: 1) {
 …
}

Bye noise #

Import, add attribute(s), have CSS fun.