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in-view

(★ 4,609)

Get notified when a DOM element enters or exits the viewport. :eyes:

File Explorer

Download Latest Version (.zip)

- in-view.min.js
- docs.webpack.config.js
- index.html
- in-view.js
- index.js
- registry.js
- viewport.js
- - setup-browser-env.js
- in-view.is.spec.js
- in-view.offset.spec.js
- in-view.spec.js
- in-view.test.spec.js
- inview.threshold.spec.js
- registry.check.spec.js
- registry.emit.spec.js
- registry.on.spec.js
- registry.once.spec.js
- registry.spec.js
- viewport.spec.js
.gitignore
.travis.yml
LICENSE
package.json
README.md
webpack.config.js

# Installation Guide

1. Get the code

git clone https://github.com/camwiegert/in-view

Downloads the entire project code from GitHub to your computer.

cd in-view

Moves into the project folder you just downloaded.

2. Node.js

Easy Recommended

Prerequisites

Git Needed to download the project code from GitHub.
Node.js Node.js must be installed to use npm. The LTS version is recommended.

npm install --save in-view

Downloads and installs the libraries listed in package.json.

✅ After running the command, open the address shown in the terminal (usually something like http://localhost:3000) in your browser.

Pulled directly from this repo's README.

// repository documentation

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# in-view.js :eyes:

Get notified when a DOM element enters or exits the viewport. A small (~1.9kb gzipped), dependency-free, javascript utility for IE9+.

[camwiegert.github.io/in-view](https://camwiegert.github.io/in-view)

[![Build Status](https://travis-ci.org/camwiegert/in-view.svg?branch=master)](https://travis-ci.org/camwiegert/in-view)
[![npm/in-view](https://img.shields.io/npm/v/in-view.svg?maxAge=2592000)](https://npmjs.com/package/in-view)

![in-view.js](https://camwiegert.github.io/in-view/lib/images/in-view.png)

---

## Installation

Either download the [latest release](https://unpkg.com/in-view/dist/in-view.min.js) and include it in your markup or install with [npm](http://npmjs.com/package/in-view):

```sh
npm install --save in-view
```

---

## Basic Usage

With in-view, you can register handlers that are called when an element **enters** or **exits** the viewport. Each handler receives one element, the one entering or exiting the viewport, as its only argument.

```js
inView('.someSelector')
    .on('enter', doSomething)
    .on('exit', el => {
        el.style.opacity = 0.5;
    });
```

---

## API

in-view maintains a separate handler registry for each set of elements captured with `inView(<selector>)`. Each registry exposes the same four methods. in-view also exposes four top-level methods. (`is`, `offset`, `threshold`, `test`).

### inView(\<selector>).on(\<event>, \<handler>)
> Register a handler to the elements selected by `selector` for `event`. The only events in-view emits are `'enter'` and `'exit'`.

> ```js
> inView('.someSelector').on('enter', doSomething);
> ```

### inView(\<selector>).once(\<event>, \<handler>)
> Register a handler to the elements selected by `selector` for `event`. Handlers registered with `once` will only be called once.

> ```js
> inView('.someSelector').once('enter', doSomething);
> ```

### inView.is(\<element>)
> Check if `element` is in the viewport.

> ```js
> inView.is(document.querySelector('.someSelector'));
> // => true
> ```

### inView.offset(\<offset>)
> By default, in-view considers something in viewport if it breaks any edge of the viewport. This can be used to set an offset from that edge. For example, an offset of `100` will consider elements in viewport if they break any edge of the viewport by at least `100` pixels. `offset` can be a positive or negative integer.

> ```js
> inView.offset(100);
> inView.offset(-50);
> ```

> Offset can also be set per-direction by passing an object.

> ```js
> inView.offset({
>     top: 100,
>     right: 75,
>     bottom: 50,
>     left: 25
> });
> ```

### inView.threshold(\<threshold>)
> Set the ratio of an element's height **and** width that needs to be visible for it to be considered in viewport. This defaults to `0`, meaning any amount. A threshold of `0.5` or `1` will require that half or all, respectively, of an element's height and width need to be visible. `threshold` must be a number between `0` and `1`.
> ```js
> inView.threshold(0);
> inView.threshold(0.5);
> inView.threshold(1);
> ```

### inView.test(\<test>)
> Override in-view's default visibility criteria with a custom function. This function will receive the element and the options object as its only two arguments. Return `true` when an element should be considered visible and `false` otherwise.
> ```js
> inView.test((el, options) => {
>     // ...
> });
> ```

### inView(\<selector>).check()
> Manually check the status of the elements selected by `selector`. By default, all registries are checked on `window`'s `scroll`, `resize`, and `load` events.

> ```js
> inView('.someSelector').check();
> ```

### inView(\<selector>).emit(\<event>, \<element>)
> Manually emit `event` for any single element.

> ```js
> inView('.someSelector').emit('exit', document.querySelectorAll('.someSelector')[0]);
> ```

---

## Browser Support

**in-view supports all modern browsers and IE9+.**

As a small caveat, in-view utilizes [MutationObserver](https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver) to check the visibility of registered elements after a DOM mutation. If that's functionality you need in IE9-10, consider using a [polyfill](https://github.com/webcomponents/webcomponentsjs/blob/master/src/MutationObserver/MutationObserver.js).

---

## Performance

Any library that watches scroll events runs the risk of degrading page performance. To mitigate this, currently, in-view only registers a single, throttled (maximum once every 100ms) event listener on each of `window`'s `load`, `resize`, and `scroll` events and uses those to run a check on each registry.

### Utilizing IntersectionObserver

There's an emerging browser API, [`IntersectionObserver`](https://wicg.github.io/IntersectionObserver/), that aims to provide developers with a performant way to check the visibility of DOM elements. Going forward, in-view will aim to delegate to `IntersectionObserver` when it's supported, falling back to polling only when necessary.

---

**License** [MIT](https://opensource.org/licenses/MIT)