in-view

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

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Installation

Either download the latest release and include it in your markup or install with npm:

npm install --save in-view

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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.

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

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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 two top-level methods. (is, offset).

inView(<selector>).on(<event>, <handler>)

Register a handler to the elements selected by selector for event. The only events the inView emits are 'enter' and 'exit'.

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.

inView('.someSelector').once('enter', doSomething);

inView.is(<element>)

Check if element is in the viewport.

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

inView.offset(<integer>)

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. integer can be positive or negative.

inView.offset(100);
inView.offset(-50);

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.

inView('.someSelector').check();

inView(<selector>).emit(<event>, <element>)

Manually emit event for any single element.

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

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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, 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.

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License MIT