🚩 trekk

About

Trekk is a library for making scroll based animations easy-peasy. Trekk does NOT give you anything else than values between 0 and 1 to use in your animation states. The animations you create yourself, or use a library like anime.js.

Install

<script src="https://unpkg.com/[email protected]/build/trekk.js"></script>

$ npm install trekk

Usage

commonJS

var trekk = require('trekk');

// Define your trails...

trekk() // Start

ES6

import trekk, { trail } from 'trekk';

// Define your trails...

trekk() // Start

API

trekk(options)

Start trekk. You need to run this only once in your scripts.

Options

Option	Type	Default	Description
debug	boolean	false	Enter debug mode.
iterate	function(next)	requestAnimationFrame	Update function.

trail(...)

Use trail to create timelines in your document. All parameters are optional.

Parameters

Param	Type	Default	Description
element	node	undefined	Pass a DOM element to use as start and end position of the trail.
startPixels	integer	undefined	Start position of the trail in pixels. If this is a nested trail this will be appended to the parent trail start position.
endPixels	integer	undefined	End position of the trail in pixels. If this is a nested trail this will be appended to the parent trail end position.
startPercentage	string	undefined	Start position of the trail in percentage. If this is a nested trail it will be a percentage of the parent trail length.
endPercentage	string	undefined	End position of the trail in percentage. If this is a nested trail it will be a percentage of the parent trail length.
progress	function(progress)	undefined	Called on update with the current progress.
options	object	{}	Object with options. See below

Options

Param	Type	Default	Description
label	string	undefined	Used as a label when debugging.
offset	function(progress)	undefined	Called on update with the current progress.
lerp	number	1	Smooth the progress over time with some linear interpolation. Takes a value from 0 to 1.
ease	string	"linear"	Easing function to run before progress is broadcasted. See Easings for supported strings.
waiting	function	undefined	Called once when the y scroll position is above the trail start position.
walking	function	undefined	Called once when the y scroll position is within the trail start and end position.
finished	function	undefined	Called once when the y scroll position is below the trail end position.

Examples

Basic

const header = document.querySelector('header')

const fadeInHeader = progress => {
	header.style.opacity = progress
}

const headerTrail = trail(header, fadeInHeader)

Nested

const header = document.querySelector('header')
const title = document.querySelector('.title')
const icon = document.querySelector('.icon')

const fadeInHeader = progress => {
	header.style.opacity = progress
}

const slideInTitle = progress => {
	title.style.transform = `translateX(${100 * progress})`
}

const rotateIcon = progress => {
	icon.style.transform = `rotate(${360 * progress}deg)`
}

const headerTrail = trail(header, fadeInHeader)
headerTrail(100, 200, slideInTitle)
headerTrail('40%', '40%', rotateIcon)

addTimeline(options)

Param	Type	Default	Description
options	object	{}	See Options

Options

Param	Type	Default	Description
label	string	"Undefined"	Used as a label when debugging.
source	function	() => window.pageYOffset	Function that returns source value.
start	function	() => 0	Function that returns start position of timeline.
end	function	0	Function that returns end position of timeline.
modifier	function	(p, s, e) => (p - s) / (e - s)	Function given a source value, calculates the progress in between the start and end value.
lerp	number	1	Smooth the progress over time with some linear interpolation. Takes a value from 0 to 1.
ease	string, function(progress)	"linear"	Easing function to run before progress is broadcasted. See Easings for supported strings, or pass your own easing function.
waiting	Called once when the y scroll position is above the trail start position.
walking	Called once when the y scroll position is within the trail start and end position.
finished	Called once when the y scroll position is below the trail end position.
progress	Called every progress update with the current progress.

Easings

// linear
// easeInQuad
// easeOutQuad
// easeInOutQuad
// easeInCubic
// easeOutCubic
// easeInOutCubic
// easeInQuart
// easeOutQuart
// easeInOutQuart
// easeInQuint
// easeOutQuint
// easeInOutQuint

Taken from https://gist.github.com/gre/1650294