React component for creating on scroll effects aka

Plx - React Parallax component

Plx - React parallax component, lightweight and powerful. Supports animating CSS properties that accept numerical values (opacity, transform, height...) and colors. It has built-in easing functions, or you can pass your own function or custom cubic bezier.

React component, for creating on scroll effects aka. parallax.
Lightweight, yet powerful.

v1.0.0 introduced breaking changes

start and duration are reworked, and end prop is introduced.
Check updated parallaxData documentation.

Quick start

Get it from npm

$ npm install --save react-plx

Import and use it in your React app.

import React, { Component } from 'react';
import Plx from 'react-plx';

class Example extends Component {
  render() {
    return (
      <Plx
        className='MyAwesomeParallax'
        parallaxData={ ... } // your parallax effects, see beneath
      >
        /* Your content */
      </Plx>
    );
  }
}

What is this?
Props
Example of props
Animation state CSS classes
Browser support
License

What is this?

This is React component which makes creating on scroll effects (aka parallax) easy. If you are not sure what it does, demo should help.

It is lightweight, and beside react, react-dom and prop-types ~~has no dependencies~~, now it has small bezier-easing package. As listening to scroll event is not performant, this component uses different approach. Interval is set (every 16ms to get 60fps) to check if scroll position is changed, and if it is, it broadcasts custom event. All of the Plx components are sharing the scroll manager singleton. Interval is set when the first component is created, and cleared when last one is unmounted. Interval time can be changed through the props, but it is shared across the components.

Elements outside of viewport are not animated. This is done by using getBoundingClientRect, but there is a known bug in iOS with getBoundingClientRect and position fixed. If you get into the same problems, you can force rendering by passing animateWhenNotInViewport={ true }.

Still you need to avoid common "don't dos" when making a parallax page:

Avoid background-size: cover
Don’t animate massive images or dramatically resize them
Avoid animating 100 things at once
Only use properties that are cheap for browsers to animate - opacity and transform (translate, rotate, skew, scale)

Read this great article to find out more (that is where I got my initial inspiration).

Of course, you can break any of these rules, but test for performance to see if it works for you.

Component is written as ES module, so it will work with webpack and other module bundlers (which is standard for React apps anyway). Tested with react-create-app and my boilerplate, Marvin.

Read more about how it works in this blog post.

Props

className string

CSS class name (it will be applied along with Plx class name).
style object

CSS style object, please note that properties used in parallax will be overridden by component.
tagName string, default div

HTML tag to be used for wrapper element.
animateWhenNotInViewport bool, default false

If set to true element will be animated even when it is not in the viewport.
This is helpful with fixed elements in iOS due to know bug with getBoundingClientRect in iOS.
disabled boolean

When true disabled animation completely.
freeze bool, default false

When true animation will be stopped at current state when condition is met.
parallaxData array of items (item structure described beneath), required

Main data, describes parallax segments.

Any other props will be passed to the component (for example this is useful for aria-* props).

parallaxData

start number, string, HTMLElement, required

Scroll position where parallax effect should start.
Can one of the following:
- Number - value in pixels
- String
  - Value in px, vh or % (50px, 50%, 25vh). Percentage is calculated out of max page scroll.
  - CSS Selector (.my-element, #some-id) to be used with document.querySelector.
  - "self" component's element will be used
- HTMLElement, given element will be used.
For element, selector and "self" animation will start when that element enters the viewport. You can use startOffset prop to offset start position.

Example:
```
start: 100 // starts when scroll hits 100px
start: 'self' // starts when plx's element enters the viewport
start: '.start-element' // starts when .start-element enters the viewport
```
PLEASE NOTE that parallaxData should be sorted by start value!
end number, string, HTMLElement

Scroll position where parallax effect should end.
It has higher priority than duration.
Can one of the following:
- Number - value in pixels
- String
  - Value in px, vh or % (50px, 50%, 25vh). Percentage is calculated out of max page scroll.
  - CSS Selector (.my-element, #some-id) to be used with document.querySelector.
  - "self" component's element will be used
- HTMLElement, given element will be used.
For element, selector and "self" animation will end when that element enters the viewport. You can use endOffset prop to offset end position.

Example:
```
end: 300 // ends when scroll hits 300px
end: 'self' // ends when plx's element enters the viewport
end: '.end-element' // ends when .end-element enters the viewport
```
duration number, string, HTMLElement

How long should effect last (it will finish
when scroll position equals start + duration).
It will be used if end is not defined.
Can one of the following:
- Number - value in pixels
- String
  - Value in px, vh or % (50px, 50%, 25vh). Percentage is calculated out of max page scroll.
  - CSS Selector (.my-element, #some-id) to be used with document.querySelector.
- HTMLElement, given element will be used.
For element and selecto animation will start when that element enters the viewport. You can use startOffset prop to offset start.

Any other string will be considered CSS selector
and it will be used with document.querySelector.
Animation will stop when animated element hits top
of the element passed as duration prop.

Example:
```
duration: 300 // animation will last for 300px
duration: '.duration-element' // animation will last for .duration-element's height
```
startOffset number, string

Start offset, can be a number or string value in px, vh or % (50px, 50%, 25vh).
endOffset number, string

End offset, can be a number or string value in px, vh or % (50px, 50%, 25vh).
easing string, function or array, default: 'linear'

Easing function, you can pass the name (string) to choose one of the built-in functions.
Built-in easing functions are:
- ease
- easeIn
- easeOut
- easeInOut
- easeInSine
- easeOutSine
- easeInOutSine
- easeInQuad
- easeOutQuad
- easeInOutQuad
- easeInCubic
- easeOutCubic
- easeInOutCubic
- easeInQuart
- easeOutQuart
- easeInOutQuart
- easeInQuint
- easeOutQuint
- easeInOutQuint
- easeInExpo
- easeOutExpo
- easeInOutExpo
- easeInCirc
- easeOutCirc
- easeInOutCirc
Cubic beziers are supported, pass an array to it with four points of your custom bezier (you can copy CSS beziers).
```
easing: [0.25, 0.1, 0.53, 3]
```
You can even pass custom function which accepts one argument, which will be number from 0 to 1.
```
// Define your custom easing
const myCustomEasing = (x) => {
  return x * x;
};

...

// and then pass it to Plx
easing: myCustomEasing
```
name string (without spaces)

Name used in animation state CSS classes
properties array of items (item structure described beneath), required

List of properties to be animated

properties

property string, required

CSS property to be animated, works only on properties which accept numerical values (e.g. opacity, height...).
For transform use function names instead (e.g. translateX, scale, rotate...).
Same goes for filters.

Supported transform functions are:
- translateX
- translateY
- translateZ
- skew
- skewX
- skewY
- skewZ
- rotate
- rotateX
- rotateY
- rotateZ
- scale
- scaleX
- scaleY
- scaleZ
Supported colors are:
- backgroundColor
- borderBottomColor
- borderColor
- borderLeftColor
- borderRightColor
- borderTopColor
- color
- fill
- strokeColor
Supported CSS filters are:
- blur
- brightness
- contrast
- grayscale
- hueRotate
- invert
- opacityFilter (as it shares the same name as CSS opacity)
- saturate
- sepia
To keep you parallax effects performant, I strongly advice not to use anything but opacity and transforms.
Some filters should be cheap as well, with blur being the most expensive out of supported filters.
startValue number (or string for color), required

Start value for the effect. Property will have this value when scroll position equals parallaxData.start.
For colors supported formats are: #123, #001122, rgb(0,0,255) and rgba(0,0,255,0.5).
endValue number (or string for color), required

End value for the effect. Property will have this value when scroll position equals parallaxData.end.
For colors supported formats are: #123, #001122, rgb(0,0,255) and rgba(0,0,255,0.5).

Between parallaxData.start and parallaxData.end value will transition relative to scroll position.
unit string

CSS unit (e.g. %, rem, em...) to be applied to property value. By default component is using pixels and degrees for rotation and skew.

Example of props

These are the exact props used in this example.

const exampleParallaxData = [
  {
    start: 0,
    end: 300,
    properties: [
      {
        startValue: 0,
        endValue: 90,
        property: "rotate"
      },
      {
        startValue: 1,
        endValue: 1.5,
        property: "scale"
      },
      {
        startValue: 1,
        endValue: 0.75,
        property: "opacity"
      }
    ]
  },
  {
    start: 350,
    duration: 300,
    properties: [
      {
        startValue: "#3cb99c",
        endValue: "rgba(50,50,200,0.8)",
        property: "backgroundColor"
      },
      {
        startValue: 0,
        endValue: 100,
        property: "translateY"
      },
      {
        startValue: 0.75,
        endValue: 1,
        property: "opacity"
      }
    ]
  },
  {
    start: 700,
    duration: 1000,
    properties: [
      {
        startValue: 100,
        endValue: 0,
        property: "translateY"
      },
      {
        startValue: 1.5,
        endValue: 2,
        property: "scale"
      },
      {
        startValue: 90,
        endValue: 0,
        property: "rotate"
      },
      // Blur is not performant
      // Used just as an example for CSS filters
      {
        startValue: 0,
        endValue: 20,
        property: "blur"
      }
    ]
  }
];

Animation state CSS classes

Component will also apply CSS classes that match current animation state.
Classes are:

Plx--above
scroll position is above first start position (animation isn't started yet)
Plx--above
scroll position is below last end position (animation is finished)
Plx--active
scroll position is below first start and last end position (animation is in progress, including between states)
Plx--in Plx--in-{n}
scroll position is in n-th segment (Plx--in-0, Plx--in-1...).
If name prop is passed (see above) it will be used instead of index (Plx--in-superDuperName).
Plx--between Plx--between-{a}-and-{b}
scroll position is between segments a and b (Plx--between-0-and-1, Plx--between-1-and-2...)
If name prop is passed (see above) it will be used instead of index (Plx--between-superDuperName-and-anotherName).

active class is applied along with both in and between classes.

Browser support

Modern browsers and IE10+.

IE9 should work if you provide a polyfill for requestAnimationFrame. But I'm not supporting IE9.