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

>> DEMO <<

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..

• Scroll effect
• Horizontal snap scroll
• Inertia
• Video/Gif playback
• Cursor position
• Text input
• Update HTML content
• Preset Explorer

• Setup
• Using presets
• Usage with UI frameworks
• Adding drivers
• Adding elements

• Custom animations
• Optimising performance

• CSS properties
• Special values
• Supported easings

# https://www.npmjs.com/package/lax.js

npm install lax.js
yarn add lax.js

import lax from 'lax.js'

<script src="path-to-lax.min.js"></script>
<!-- or via CDN -->
<script src="https://cdn.jsdelivr.net/npm/lax.js" ></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 -->
<script>
  window.onload = function () {
    lax.init()

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

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

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

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.

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.

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.

lax.addDriver(
  'scrollY',                          // Driver name
  function(laxFrame) {                     
    return window.scrollY    // Value method
  },
  { }                                 // Options
)

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.

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.

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

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

Add static CSS to each element, for example:

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

Pass references to raw DOM elements to allow for more flexible selection patterns. In this case, a unique selector must still be passed as the first argument, however it does not need to be a valid DOM selector.

This allows the library to tag the elements for removal later. Example:

const myDomElements = $('.selector')

{
  elements: myDomElements
}

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: [  // Driver name
    100,      // Driver value
    0         // Driver inertia
  ]
}

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
    ]
  }
}

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.

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.

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 driver value maps and 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
    },
  ];
}

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.

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.

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

See inertia in action here.

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

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

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)`;
};

See a list of available values here.

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.