basicscroll

basicScroll

Standalone parallax scrolling for mobile and desktop with CSS variables.

basicScroll allows you to change CSS variables depending on the scroll position. Use the variables directly in your CSS to animate whatever you want. Highly inspired by skrollr and Reactive Animations with CSS Variables.

Contents

• Demos
• Features
• Requirements
• Setup
• API
• Instance API
• Data
• Tips

Demos

Name	Description	Link
Default	Includes most features.	Try it on CodePen
Parallax scene	A composition of multiple, moving layers.	Try it on CodePen

Features

• Zero dependencies
• CommonJS and AMD support
• Simple JS API
• Insane performance
• Support for mobile and desktop

Requirements

basicScroll depends on the following browser features and APIs:

• CSS Custom Properties
• requestAnimationFrame

Some of these APIs are capable of being polyfilled in older browsers. Check the linked resources above to determine if you must polyfill to achieve your desired level of browser support.

Setup

We recommend to install basicScroll using Bower or npm.

bower install basicScroll

npm install basicscroll

Include the JS file at the end of your body tag…

<script src="dist/basicScroll.min.js"></script>

…or skip the JS file and use basicScroll as a module:

const basicScroll = require('basicScroll')

Usage

This demo shows how to to change the opacity of an element when the user scrolls. The element starts to fade as soon as the top of the element reaches the bottom of the viewport. A opacity of .99 is reached when the middle of the element is in the middle of the viewport.

Tip: Animating from .01 to .99 avoids the repaints that normally occur when the element changes from fully transparent to translucent and from translucent to fully visible.

const instance = basicScroll.create({
	elem  : document.querySelector('.element'),
	from  : 'top-bottom',
	to    : 'middle-middle',
	props : {
		'--opacity': {
			from : '.01',
			to   : '.99'
		}
	}
})

instance.start()

.element {
	/*
	 * Use the same CSS variable as specified in out instance.
	 */
	opacity: var(--opacity);
	/*
	 * The will-change CSS property provides a way for authors to hint browsers about the kind of changes
	 * to be expected on an element, so that the browser can setup appropriate optimizations ahead of time
	 * before the element is actually changed.
	 */
	will-change: opacity;
}

API

.create(html, opts)

Creates a new basicScroll instance.

Be sure to assign your instance to a variable. Using your instance, you can…

• …start and stop the animation.
• …check if the instance is active.
• …get the current props.

Examples:

const instance = basicScroll.create({
	from  : '0',
	to    : '100px',
	props : {
		'--opacity': {
			from : '0',
			to   : '1'
		}
	}
})

const instance = basicScroll.create({
	elem  : document.querySelector('.element'),
	from  : 'top-bottom',
	to    : 'bottom-top',
	props : {
		'--translateY': {
			from   : '0',
			to     : '100%',
			timing : 'elasticOut'
		}
	}
})

const instance = basicScroll.create({
	elem    : document.querySelector('.element'),
	from    : 'top-middle',
	to      : 'bottom-middle',
	inside  : (instance, percentage) => {
		console.log('viewport is inside from and to')
	},
	outside : (instance, percentage) => {
		console.log('viewport is outside from and to')
	}
})

Parameters:

• data {Object} An object of data.

Returns:

• {Object} The created instance.

Instance API

Each basicScroll instance has a handful of handy functions. Below are all of them along with a short description.

.start()

Starts to animate the instance. basicScroll will track the scroll position and adjust the props of the instance accordingly. An update will be performed only when the scroll position has changed.

Example:

instance.start()

.stop()

Stops to animate the instance. All props of the instance will keep their last value.

Example:

instance.stop()

.update()

Triggers an update of an instance, even when the instance is currently stopped.

Example:

instance.update()

Returns:

• {Array} New props. An array of objects, each with a key and value.

.calculate()

Converts the start and stop position of the instance to absolute values. basicScroll relies on those values to start and stop the animation at the right position. It runs the calculation once during the instance creation. .calculate() should be called when elements have altered their position or when the size of the site/viewport has changed.

Example:

instance.calculate()

.isActive()

Returns true when the instance is started and false when the instance is stopped.

Example:

instance.isActive()

Returns:

• {Boolean}

.getData()

Returns calculated data. More or less a parsed version of the data used for the instance creation. The data might change when calling the calculate function.

Example:

instance.getData()

Returns:

• {Object} Parsed data.

Data

The data object can include the following properties:

{
	/*
	 * DOM Element/Node.
	 */
	elem: null,
	/*
	 * Start and stop position.
	 */
	from  : null,
 	to    : null,
	/*
	 * Callback functions.
	 */
	inside  : (instance, percentage) => {},
	outside : (instance, percentage) => {},
	/*
	 * Props.
	 */
	props: {
		/*
		 * Property name / CSS Custom Properties.
		 */
		'--name': {
			/*
			 * Start and end values.
			 */
			from : null,
			to   : null,
			/*
			 * Animation timing.
			 */
			timing: 'ease',
			/*
			 * Direct mode.
			 */
			direct: false
		}
	}
}

DOM Element/Node

Type: Node Default: null Optional: true

A DOM Element/Node.

The position and size of the element will be used to convert the start and stop position to absolute values. How else is basicScroll supposed to know when to start and stop an animation with relative values?

You can skip the property when using absolute values.

Example:

{
	elem: document.querySelector('.element')
	/* ... */
}

Start and stop position

Type: Integer|String Default: null Optional: false

basicScroll starts to animate the props when the scroll position is above from and below to. Absolute and relative values are allowed. Relative values require a DOM Element/Node.

Examples:

{
	/* ... */
	from : '0px',
	to   : '100px',
	/* ... */
}

{
	/* ... */
	from : 'top-middle',
	to   : 'bottom-middle',
	/* ... */
}

Callback functions

Type: Function Default: () => {} Optional: true

• The inside callback executes when the user scrolls and the viewport is within the given start and stop position.
• The outside callback executes when the user scrolls and the viewport is outside the given start and stop position.

Both callbacks receive the current instance and a percentage:

• < 0% percent = Scroll position is below from
• = 0% percent = Scroll position is from
• = 100% percent = Scroll position is to

• 100% percent = Scroll position is above from

Example:

{
	/* ... */
	inside  : (instance, percentage) => {},
	outside : (instance, percentage) => {},
	/* ... */
}

Props

Type: Object Default: {} Optional: true

Values to animate when the scroll position changes.

Each prop of the object represents a CSS property or CSS Custom Property (CSS variables). Custom CSS properties always start with two dashes. A prop with the name --name is accessible with var(--name) in CSS.

More about CSS custom properties.

Example:

{
	/* ... */
	props: {
		'--one-variable': { /* ... */ },
		'--another-variable': { /* ... */ }
	}
}

Start and end values

Type: Integer|String Default: null Optional: false

Works with all kinds of units. basicScroll uses the unit of to when from has no unit.

Examples:

'--name': {
	/* ... */
	from : '0',
	to   : '100px',
	/* ... */
}

'--name': {
	/* ... */
	from : '50%',
	to   : '100%',
	/* ... */
}

'--name': {
	/* ... */
	from : '0',
	to   : '1turn',
	/* ... */
}

Animation timing

Type: String|Function Default: linear Optional: true

A known timing or a custom function. Easing functions get just one argument, which is a value between 0 and 1 (the percentage of how much of the animation is done). The function should return a value between 0 and 1 as well, but for some timings a value less than 0 or greater than 1 is just fine.

Known timings: backInOut, backIn, backOut, bounceInOut, bounceIn, bounceOut, circInOut, circIn, circOut, cubicInOut, cubicIn, cubicOut, elasticInOut, elasticIn, elasticOut, expoInOut, expoIn, expoOut, linear, quadInOut, quadIn, quadOut, quartInOut, quartIn, quartOut, quintInOut, quintIn, quintOut, sineInOut, sineIn, sineOut

Examples:

'--name': {
	/* ... */
	timing: 'circInOut'
}

'--name': {
	/* ... */
	timing: (t) => t * t
}

Direct mode

Type: Boolean Default: false Optional: true

basicScroll applies all props globally by default. This way you can use variables everywhere in your CSS, even when the instance tracks just one element. Set direct to true to apply styles directly to the DOM Element/Node. Setting direct to true also allows you to animate CSS properties, not just CSS variables.

Examples:

<!-- direct: false -->
<html style="--name: 0;">
	<div class="element"></div>
</html>

<!-- direct: true -->
<html>
	<div class="element" style="--name: 0;"></div>
</html>

Tips

• Only animate transform and opacity and use will-change to hint browsers about the kind of changes. This way the browser can setup appropriate optimizations ahead of time before the element is actually changed.
• Keep the amount of instances low. More instances means more checks, calculations and style changes.
• Don't animate everything at once and don't animate too many properties. Browsers don't like this.
• Smooth animations by adding a short transition to the element: transform: translateY(var(--ty)); transition: transform .1s.
• basicScroll applies all props globally by default. Try to reuse variables across elements instead of creating more instances.