Awesome Scroll Effects In JavaScript – lax.js

Awesome Scroll Effects In JavaScript – lax.js

Simple & lightweight (<4kb gzipped) vanilla JavaScript library to create smooth & beautiful animations when you scroll.


Simple & lightweight (<4kb gzipped) vanilla JavaScript library to create smooth & beautiful animations when you scroll.

Lax 2.0 Gif

What's new with Lax.js 2.0

Lax.js 2.0 has been completely re-written with a focus on modularity and flexibility giving you more tools to create awesome animations.

  • New javascript animation syntax, allowing for more advanced effect combos
  • Use any value to drive animations, for example mouse position, time of day .. and of course scroll!
  • Animations can be given inertia when scrolling
  • Create custom CSS bindings
  • Animation easings
  • And much more..


Getting started

NPM Setup


npm install lax.js
yarn add lax.js
import lax from 'lax.js'

HTML setup

<script src="path-to-lax.min.js"></script>
<!-- or via CDN -->
<script src="" ></script>


To implement lax you need to create at least one driver, to provide values for animations, as well as the element animation bindings. Below is a simple example:

<!-- JS -->
  window.onload = function() {

    // Add a driver that we use to control our animations
    lax.addDriver('scrollY', function() {
      return document.body.scrollTop

    // Add animation bindings to elements
    lax.addElements('.selector', {
      scrollY: {
        translateX: [
          ["elInY", "elCenterY", "elOutY"],
          [0, 'screenWidth/2', 'screenWidth'],

<!-- HTML -->
<div class="selector">Hello</div>

Using presets

The easiest way to get started is to use presets via html classes. For example:

<div class="lax lax_preset_fadeIn-50-100 lax_preset_spin"></div>

Multiple presets can be chained together and they can be customised to suit your needs. Use the preset explorer to explore effects and see a simple example here.

DOM behavior and usage with Frameworks

To increase performance, lax.js indexes the list of elements to animate when the page loads. If you're using a library like React, Vue or EmberJS, it is likely that you are adding elements after the initial window.onload. Because of this you will need to call lax.addElements when you add components to the DOM that you want to animate, and lax.removeElements when the component unmounts.

Please find a React example here. Other examples will be available soon for Vue.js and Angular.

Adding drivers

Drivers provide the values that drive your animations. To set up a driver just call lax.addDriver with a name and a function which returns a number. This method is called every frame to calculate the animations so keep the method as computationally light as possible. The example below will be the most common use case for lax which returns the scrollY position of the window.

  'scrollY',                          // Driver name
  function(laxFrame) {                     
    return document.body.scrollTop    // Value method
  { }                                 // Options

Driver options

inertiaEnabled: boolean = false

If enabled, the driver will calculate the speed at which its value is changing. Used to add inertia to elements using the inertia element option.

See this in action in the here.

frameStep: number = 1

By default each driver updates its value every animation frame, around ~60 times per second. You can use the frameStep to reduce frequency of the driver value updating. For example a value of 2 would only update ~30 times per second and a value of 60 would only update about once per second.

Adding elements

You can add lax animations to an element using the addElements method:

  '.selector',  // Element selector rule
  {             // Animation data
    scrollY: {  
      opacity: [
        [0, 100],
        [1, 0]
    style: {}   // Element options

Element options

style: StyleObject

Add static CSS to each element, for example:

  transform: '200ms scale ease-in-out';

Going deeper

Custom animations

Custom animations are defined using an object.

// Animation data
  scrollY: {                // Driver name
    translateX: [           // CSS property
      ['elInY', 'elOutY'],  // Driver value map
      [0, 'screenWidth'],   // Animation value map
        inertia: 10        // Options
    opacity: [
      // etc

Driver name

The name of the driver you want to use as a source of values to map to your animation, for example, the document's scrollY position. Read about adding drivers here.

CSS property

The name of the CSS property you want to animate, for example opacity or rotate. See a list of supported properties here.

Some css properties, for example box-shadow, require a custom function to build the style string. To do this use the cssFn element option.

Value maps

The value maps are used to interpolate the driver value and output a value for your CSS property. For example:

[0, 200, 800]  // Driver value map
[0, 10,  20]   // Animation value map

// Result

| In  | Out |
| --- | --- |
| 0   | 0   |
| 100 | 5   |
| 200 | 10  |
| 500 | 15  |
| 800 | 20  |

Within the maps you can use strings for simple formulas as well as use special values. e.g:

['elInY', 'elCenterY-200', 'elCenterY',

See a list of available values here.

You can also use mobile breakpoints within animation maps for more flexibility.

scrollY: {
  translateX: [
    ['elInY', 'elCenterY', 'elOutY'],
      500: [10, 20, 50], // Screen width < 500
      900: [30, 40, 60], // Screen width > 500 and < 900
      1400: [30, 40, 60], // Screen width > 900


modValue: number | undefined

Set this option to modulus the value from the driver, for example if you want to loop the animation value as the driver value continues to increase.

frameStep: number = 1

By default each animation updates its value every animation frame, around ~60 times per second. You can use the frameStep to reduce frequency of the animation updating. For example a value of 2 would only update ~30 times per second and a value of 60 would only update about once per second.

inertia: number

Use to add inertia to your animations. Use in combination with the inertiaEnabled driver option.

See inertia in action here.

inertiaMode: "normal" | "absolute"

Use in combination with inertia. If set to absolute the inertia value will always be a positive number via the Math.abs operator.

cssUnit: string = ""

Define the unit to be appended to the end of the value, for example For example px deg

onUpdate: (driverValues: Object, domElement: DomElement) => void

A method called every frame with the current driverValues and domElement. This could be used to toggle classes on an element or set innerHTML. See it in action here.

The driver values are formatted as follows:

  scrollY: [  // Drivr name
    100,      // Driver value
    0         // Driver inertia

cssFn: (value: number) => string

Some CSS properties require more complex strings as values. For example, box-shadow has multiple values that could be modified by a lax animation.

// Box-shadow example
(val) => {
  return `${val}px ${val}px ${val}px rgba(0,0,0,0.5)`;

Optimising performance

Lax.js has been designed to be performant but there are a few things to bare in mind when creating your websites.

  • Smaller elements perform better.
  • Postion fixed and absolute elements perform best as they do not trigger a layout change when updated.
  • Off-screen elements do not need to be updated so consider that when creating your animation value maps.
  • The css properties blur, hue-rotate and brightness are graphically intensive and do not run as smoothly as the other available properties.


CSS properties


Special values

key value
screenWidth current width of the screen
screenHeight current height of the screen
pageWidth width of the document
pageHeight height of the document
elWidth width of the element
elHeight height of the element
elInY window scrollY position when element will appear at the bottom of the screen
elOutY window scrollY position when element will disappear at the top of the screen
elCenterY window scrollY position when element will be centered vertically on the screen
elInX window scrollX position when element will appear at the right of the screen
elOutX window scrollX position when element will disappear at the left of the screen
elCenterX window scrollX position when element will be centered horizontally on the screen
index index of the element when added using lax.addElements

Supported easings


Download Details:

Author: alexfoxy


Source Code:


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