intersection-observer

Features

- Lazy loading of images or other content as the page scrolls.
- Implementation of "infinity scrolling" sites, where new content is loaded and displayed as you scroll.
- Reporting on the visibility of the site's promotional blocks to calculate effectiveness.
- Deciding whether to perform tasks or animations depending on whether the user sees the result.

W3C Documentation

API

$3

Library has a polyfill taken from W3C (which was moved and archived in GoogleChromeLabs/intersection-observer).

The polyfill isn't included into the bundle. If you need to support old browsers, call requirePolyfill on client app initialization to verify if client needs it and require dynamically the polyfill script. It should be done before App become interactive, use callback for more control.

``jsx
// client
import { requirePolyfill } from '@locmod/intersection-observer'


requirePolyfill(() => {
setIntersectionObserverReady(true)
renderApp()
whatever()
})

`
Or use polyfill.io instead:
`html

`

$3

Calls rerender on each change of entry state.

`js
const [ ref, entry, unobserve ] = useEntry(options)
`

$3

Entry changes call listener callback, it doesn't have a state, so doesn't rerender a component.

`ts
const listener = (entry: IntersectionObserverEntry) => {}

const [ ref, unobserve ] = useEntryListener(listener, options)
`

$3

`
{
// IntersectionObserver options
observerProps: {
root: node,
rootMargin: '10px 10px 10px 10px',
threshold: [ 0, 0.25, 0.5, 0.75, 1 ],
},
// event will be fired once and then unsubscribed from observer
once: true,
}
`

Read more about IntersectionObserver options.

Examples

$3

`jsx
const App = () => {
const [ ref, entry ] = useEntry()

const isVisible = !entry || !entry.isIntersecting

return (