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https://github.com/firstandthird/scroll-triggers

Javascript library to trigger various things as a user scrolls down the page
https://github.com/firstandthird/scroll-triggers

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Javascript library to trigger various things as a user scrolls down the page

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# scroll-triggers ![npm](https://img.shields.io/npm/v/scroll-triggers.svg)

A tiny, dependency-less javascript library to add classes as elements scroll into viewport.

## Features

* Add a class when an element comes into view (great for animations)
* Set an image when an element comes into view (great for lazy loading)
* Set the width of an element based on scroll % (great for scroll progress bars)
* API for both HTML and Javascript

## Install

```sh
npm install scroll-triggers
```

## Setup

```javascript
import 'scroll-triggers';

// alternative
import scrollTriggers from 'scroll-triggers';
```

## Events

Custom events are fired/listened on the element:

| Event | Type | Description |
|----------------------------|----------|-------------------------|
| `scrolltriggers:inView` | Fired | Element is in view |
| `scrolltriggers:outOfView` | Fired | Element is out of view |
| `scrolltriggers:pause` | Listened | Pauses scroll-triggers |
| `scrolltriggers:resume` | Listened | Resumes scroll-triggers |

## Options

List of available options:

| Name | Type | Description |
|---------------|---------------------------------------------------|--------------------------------------------------------------------------|
| `className` | _{string}_ | Class to be added/removed when element is in view |
| `start` | _{string\|Element\|NodeList}_ CSS Selector | Add class when the specified element is in view |
| `end` | _{string\|Element\|NodeList}_ CSS Selector | Removes class when the specified element is in view |
| `position` | _{string = 'bottom'}_ "top\|middle\|bottom" | Add class at when element hits the specified position of page |
| `positionEnd` | _{string = 'bottom'}_ "auto\|top\|middle\|bottom" | Removes class when specified element hits the specified position of page |
| `offset` | _{number}_ | The offset controls the distance (negative or positive) between the top border of the element and the top border of the window. This is useful to fine tune when a class is added. |
| `image` | _{string}_ Path to image | Set an image when an element comes into view, if the element is an it will set it as the src, otherwise it will be set as `background-image` |
| `src` | _{string}_ Path to resource | Set the `src` property when an element comes into view |
| `srcset` | _{string}_ Path to resource | Set the `srcset` property when an element comes into view |
| `progress` | _{boolean = false}_ | Set the width of an element based on scroll % |
| `once` | _{boolean = true}_ | Whether scroll-triggers should be executed once or not |
| `fixed` | _{boolean = true}_ | Needed for fixed (`position: fixed`) elements |
| `inView` | _{function}_ | Callback executed when element is in view |
| `outOfView` | _{function}_ | Callback executed when element is out view |

## Usage

See [the example](example/index.html).

### HTML

Add class when element is in view.

```html


```

Add class when another element is in view

```html


```

Add class when another element is in view and remove when it gets to another element

```html


```

Add class at when element hits bottom of page

```html


```

Add class at when element hits middle of page

```html


```

Set an image when an element comes into view as a background image

```html

```

Set the width of an element based on scroll % (great for progress bars)

```html


```

Set the `src` property when an element comes into view (great for lazy load)

```html

```

Set the `srcset` property when an element comes into view (great for lazy load)

```html

```

### JavaScript

```javascript
import scrollTriggers from 'scroll-triggers';

scrollTriggers([
{
el: '.some-selector',
start: '.selector',
end: '.selector',
className: 'class-to-add',
image: 'image/path.jpg',
src: 'http://url-to-resource.com',
srcSet: 'http://url-to-resource.com',
position: 'top|middle|bottom',
positionEnd: 'auto|top|middle|bottom',
offset: -20,
progress: true|false,
once: true|false,
fixed: true|false,
inView: (el, options) => {},
outOfView: (el, options) => {}
}
]);
```