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Scrollerful

By Rémino Rem https://remino.net

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

⚠️ 2024-08-05: 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 use the Scroll-driven Animations module in CSS now supported by Chrome, instead of Scrollerful, along with the polyfill for browsers that don't yet support it, like Firefox and Safari.

Demo | Code

About

demo.mp4

What is it?

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.

How does it work?

  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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Built With

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Getting Started

There are some ways to get Scrollerful:

Via CDN

Link its auto-start script via unpkg.org:

<script defer src="https://unpkg.com/[email protected]/dist/scrollerful-auto.min.js"></script>

Via npm

Get it via npm:

npm add scrollerful

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

// Using ES6 import
import scrollerful from 'scrollerful'

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

// Start it
scrollerful()

Download

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 formats. Back to top

Usage

Step 1. Define your HTML:

<div class="sclf">
    <div class="sclf__float">
        <div class="bg sclf__sprite"></div>
        <div class="toy sclf__sprite--contain"></div>
    </div>
</div>

Step 2. Define your CSS with animation keyframes:

@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:

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

Control when the animation starts and ends

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

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

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

Applying multiple animations with different timings

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.

.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.

Animating only when the container covers the viewport

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.

Limited support for the new animation-timeline

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.

Horizontal scrolling

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 <body>:

<body class="sclf--x">
    <div class="sclf">
        <div class="sclf__float">
            <div class="bg sclf__sprite"></div>
            <div class="toy sclf__sprite--contain"></div>
        </div>
    </div>
</body>

Snapping

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

<html class="sclf--snap">

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

Make the whole page the container

You can! Just set the sclf class on <body>:

<body class="sclf">

Make sprites animate but without the floater

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:

<div class="sclf">
    <div class="bg sclf__sprite"></div>
    <div class="toy sclf__sprite--contain"></div>
</div>

Animating the <body> itself.

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

<body class="sclf__sprite">
.sclf--enabled body {
	animation-name: bg;
}

/* Ensure the <html> 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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