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import { useEvent } from '@wordpress/compose';
import { useState, useEffect } from 'react';
/**
* Tracks if an element contains overflow and on which end by tracking the
* first and last child elements with an `IntersectionObserver` in relation
* to the parent element.
*
* Note that the returned value will only indicate whether the first or last
* element is currently "going out of bounds" but not whether it happens on
* the X or Y axis.
*/
export function useTrackOverflow(
parent: HTMLElement | undefined | null,
children: {
first: HTMLElement | undefined | null;
last: HTMLElement | undefined | null;
}
) {
const [ first, setFirst ] = useState( false );
const [ last, setLast ] = useState( false );
const [ observer, setObserver ] = useState< IntersectionObserver >();
const callback: IntersectionObserverCallback = useEvent( ( entries ) => {
for ( const entry of entries ) {
if ( entry.target === children.first ) {
setFirst( ! entry.isIntersecting );
}
if ( entry.target === children.last ) {
setLast( ! entry.isIntersecting );
}
}
} );
useEffect( () => {
if ( ! parent || ! window.IntersectionObserver ) {
return;
}
const newObserver = new IntersectionObserver( callback, {
root: parent,
threshold: 0.9,
} );
setObserver( newObserver );
return () => newObserver.disconnect();
}, [ callback, parent ] );
useEffect( () => {
if ( ! observer ) {
return;
}
if ( children.first ) {
observer.observe( children.first );
}
if ( children.last ) {
observer.observe( children.last );
}
return () => {
if ( children.first ) {
observer.unobserve( children.first );
}
if ( children.last ) {
observer.unobserve( children.last );
}
};
}, [ children.first, children.last, observer ] );
return { first, last };
}
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