👻 Minimal library to observe nodes entering and leaving the viewport.

Be sure to also check the Intersection Observer API, a native solution which works in modern browsers, if you want to know more I wrote an introduction article explaining how it works.

# npm
npm i huntjs --save

# yarn
yarn add huntjs

Or include it as a script with //unpkg.com/huntjs/dist/hunt.umd.js as source.

The package exposes an observer that receives a Node, NodeList or Array as a first argument and an object as a second argument with the desired set of options.

import Hunt from 'huntjs';

// lazy loading images using dataset and hunt
const lazyImages = document.querySelectorAll('img.lazy');

let observer = new Hunt(lazyImages, {
  enter: (image) => image.src = image.dataset.src
});

Check this example working here

By default the observer will stop hunting elements when they enter and then leave the viewport.

These are the properties you can set as a configuration:

• enter, function called when the element becomes visible.
• leave, function method called when the element leaves completely the viewport.

Both callbacks will receive the element which triggered the action as argument.

• persist, boolean and false by default which indicates if the targets should still be observed after they entered and left the viewport. When this option is true enter and leave methods will be called each time an element state changes. Recommended for constant animations triggered by scroll events.
• offset, number that defines a number of pixels ahead of the element's state change, 0 being the default value. Good if you want to start loading an image before the user reaches to it.
• throttleInterval, number interval use for event throttling. A lower number will mean elements are detected in view quicker, but may degrade performace. A higher value will mean elements are detected in view slower, but may improve performance. The default value is 100, is recommended not to modify this.

If you need exceptions over config for one or more elements, data-hunt-offset and data-hunt-persist attributes can be used. These custom values will override the ones you passed to the observer.

<div
  class="observed--element"
  data-hunt-persist="true"
  data-hunt-offset="500"
>
</div>

JSON.parse is used on these values at runtime, make sure to pass safe content.

To contribute Node.js and yarn are required.

Before commit make sure to follow conventional commits specification and check all tests pass by running yarn test.