Scrollerful

By Rémino Rem

JavaScript library using CSS variables to animate elements while user scrolls.

⚠️ 2025-05-28: If you only want scroll animations in CSS and you don't need
to add JavaScript knowing the position of the scroll, I recommend you also look
into the
Scroll-driven Animations module in CSS
now supported by Chrome. There is also a
polyfill for browsers that don't
yet support it, like Firefox and Safari, but doesn't work for all cases.

Demo |
Code

- About
- What is it?
- How does it work?
- Built With
- Getting Started
- Via CDN
- Via npm
- Download
- Usage
- Tips
- Control when the animation starts and ends
- Applying multiple animations with different timings
- Animating only when the container covers the viewport
- Limited support for the new animation-timeline
- Horizontal scrolling
- Snapping
- Make the whole page the container
- Make sprites animate but without the floater
- Animating the itself.
- Contributing
- License
- Contact

About

https://github.com/remino/scrollerful/assets/29999/9dba06bb-6cc7-434c-8ad0-a56101809890

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Scrollerful is a tiny JavaScript library of around 1 KB brotlied that works
with some stylesheet it inserts in the HTML to control CSS animations while
scrolling.

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1. You set a _floater_ in a _container_ with _sprites_ (or elements) to animate.
2. When you scroll, the library checks to see how much of the container has been
scrolled in and out the viewport, while the floater with its sprites remains
entirely visible.
3. The library sets some CSS variables to indicate how much as been scrolled and
what point of the animation should be displayed, effectively animating
sprites will scrolling.

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- JavaScript
- Sass
- rollup.js
- Docs:
- Middleman
- mansite

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Getting Started

There are some ways to get Scrollerful:

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Link its auto-start script via unpkg.org:

``html
defer
src="https://unpkg.com/scrollerful@1.0.0/dist/scrollerful-auto.min.js">
`

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Get it via npm:

`sh
npm add scrollerful
`

The package comes with ES and CommonJS modules, which you can import in your
code:

`js
// Using ES6 import
import scrollerful from 'scrollerful'

// Using CommonJS require
const scrollerful = require('scrollerful')

// Start it
scrollerful()
`

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You can simply
get the package on GitHub or clone the
repo from there. The script is bundled as modules both in CommonJS and ES
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Usage

Step 1. Define your HTML:

`html


`css
@keyframes bg {
from {
background-color: #000;
}

to {
background-color: #fff;
}
}

@keyframes toy {
from {
border-radius: 100%;
color: #fff;
transform: rotate(0) scale(1);
}

to {
border-radius: 0;
color: #000;
transform: rotate(1turn) scale(1.4);
}
}

.sclf--enabled .bg {
animation-name: bg;
inset: 0;
position: absolute;
z-index: -1;
}

.sclf--enabled .toy {
animation-name: toy;
height: 6rem;
width: 6rem;
}
`

Step 3. Define your JavaScript to respond to events and start
Scrollerful:

`js
import scrollerful from 'scrollerful'

const SYMBOLS = '🛑✋😳🔶⌛🏃🤔💭😃👍✅'
const symbol = percentage => SYMBOLS[Math
.round(percentage / SYMBOLS.length)]
const clamp = (val, min, max) = Math
.max(min, Math.min(max, val))

// Show emoji based on how much has been scrolled:
const showContainProgress = ({
detail: { progress: { contain: progress } }
}) => {
document.querySelector('.toy').textContent =
symbol(clamp(Math.round(progress * 100), 0, 100))
}

const main = () => {
document.querySelector('.sclf')
.addEventListener('sclf:scroll', showContainProgress)

scrollerful()
}

main()
`

Step 4. Try it!

See the above in action

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Tips

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You can set some CSS variables to begin an animation far after scrolling into
the container, or finish it before reaching the end.

`css
.sclf--enabled .toy {
/ Start animation when scrolling at a quarter: /
--sclf-delay: 25;

/ End animation when scrolling at three quarters: /
--sclf-duration: 75;
}
`

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It’s doable, but tricky and reserved for the pros. The variables used to control
single animations cannot work with multiple ones. You will also have to manage
the animation-range for the animation-timeline yourself.

`css
.sclf--enabled .toy {
animation-delay:
calc(var(--sclf-progress-contain, 0) * -100s + 25s),
calc(var(--sclf-progress-contain, 0) * -100s + 50s),
calc(var(--sclf-progress-contain, 0) * -100s + 0s);

animation-duration: 50s, 50s, 25s;

animation-range:
contain 25% contain 75%,
contain 50% contain 100%,
contain 0% contain 25%;
}
`

Let’s take the values for the first animation above for example:

1. Every second here is a percent of scrolling of the sprite’s container.
2. Its delay is set to 25 seconds, so starts when scrolling at 25%.
3. Its duration is set to 50 seconds, so plus the delay, ends when reaching 75%.
4. As a contain sprite is animated only when the container fills the viewport,
its matching animation-range should be when the sprite’s container is
contained within the viewport, from 25% to 75%. Thus
contain 25% contain 75%. (For cover sprites, it would be cover instead
of contain.)

Note: if you only set one animation, or all your animations have the same delay
and duration, this library takes care of that for you.

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There are two kinds of sprites: cover and contain. For cover, the default,
animate the moment we see any glimpse of its container. As for contain, the
animation only begins when the container covers the whole viewport, i.e. when
its top reaches the top of the browser’s window.

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CSS scroll animations are coming with animation-timeline and a handful of
other properties.

To improve animation performance, this library automatically works with then if
the browser supports it.

However, keep in mind that the specs for
CSS scroll animations may change. At
the moment, only Chrome support them by default, and Firefox as well when its
layout.css.scroll-driven-animations.enabled flag is enabled.

That said, animation-timeline cannot emit events like Scrollerful
does—that’s exclusive to JavaScript.

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You can achieve horizontal scrolling (scrolling along the X axis) by wrapping
containers in an element with the sclf--x CSS, or simply adding that class in
the :

`html



You can enable snapping to the edges of containers by adding the sclf--snap
class to :

`html

`

However, while it works fine in Firefox and Safari, that looks broken in Chrome.
(Yeah, I know that’s not good.)

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You can! Just set the sclf class on :

`html

`

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The floater is optional. If you want to put sprites all over the page and just
have them animate in place, just omit it. For example:

`html


You can animate the itself by adding the sclf__sprite class thus
turning it into a sprite:

`html

`

`css
.sclf--enabled body {
animation-name: bg;
}

/ Ensure the has a proper flexible height. /
html {
min-height: 100%;
}
`

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Contributing

Contributions are what make the open source community such an amazing place to
learn, inspire, and create. Any contributions you make are **greatly
appreciated**.

If you have a suggestion that would make this better, please fork the repo and
create a pull request. You can also simply open an issue with the tag
"enhancement". Don't forget to give the project a star! Thanks again!

1. Fork the Project
2. Create your Feature Branch (git checkout -b feature/AmazingFeature)
3. Commit your Changes (git commit -m 'Add some AmazingFeature')
4. Push to the Branch (git push origin feature/AmazingFeature)
5. Open a Pull Request

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License

Distributed under the ISC License. See LICENSE.txt` for more information.

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Contact

Rémino Rem https://remino.net/

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