mediawiki-skins-Citizen/resources/skins.citizen.scripts/scrollObserver.js

/**
 * Create an observer for showing/hiding feature and for firing scroll event hooks.
 * Based on Vector
 *
 * @param {Function} show functionality for when feature is visible
 * @param {Function} hide functionality for when feature is hidden
 * @return {IntersectionObserver}
 */
function initScrollObserver( show, hide ) {
	/* eslint-disable-next-line compat/compat */
	return new IntersectionObserver( ( entries ) => {
		if ( !entries[ 0 ].isIntersecting && entries[ 0 ].boundingClientRect.top < 0 ) {
			// Viewport has crossed the bottom edge of the target element.
			show();
		} else {
			// Viewport is above the bottom edge of the target element.
			hide();
		}
	} );
}

module.exports = {
	initScrollObserver
};