@pronotron/io

Reliable viewport tracking without missed targets, unlike the default IntersectionObserver API. Built on @native-control-table, it can safely be used for parallax effects, lazy loading, or tracking when any part of an element enters or exits the screen. Suitable for implementing any custom scrolling application.

Setup

import { PronotronIOVertical } from '@pronotron/io';

const pronotronIO = new PronotronIOVertical();

const onScroll = () => {
	pronotronIO.handleScroll( window.scrollY )
	setScrollDirection( pronotronIO.direction );
};

const onResize = () => {
	pronotronIO.setViewport( window.innerHeight, document.documentElement.scrollHeight );
	pronotronIO.setLastScrollY( 0 );
	pronotronIO.handleScroll( window.scrollY );
	setScrollDirection( pronotronIO.direction );
};

/**
 * TIP: It's better to use with a throttle function and RequestAnimationFrame API to optimize 
 */
window.addEventListener( 'scroll', onScroll, { passive: true } );

/**
 * (x) window.addEventListener( 'resize', onResize );
 * 
 * - Do not use window.resize event, it's firing every scroll in mobile devices because of topbar behavior.
 * - May use ResizeObserverPolyfill from '@juggle/resize-observer' to support old devices.
 */
const ResizeObserver = window.ResizeObserver | ResizeObserverPolyfill;
const ro = new ResizeObserver(( entries, observer ) => {
	onResize();
});

ro.observe( document.body );

Observing

const element = document.getElementByID( "test" );

const nodeID = pronotronIO.addNode({
	ref: element,
	dispatch: {
		onTopIn: () => console.log( "Top-in" ),
		onTopOut: () => console.log( "Top-out" ),
		onBottomIn: () => console.log( "Bottom-in" ),
		onBottomOut: {
			retry: 3,
			dispatch: () => console.log( "Bottom-out" ),
		},
		// Returns -1 to +1 normalized position
		onInViewport: ( normalizedPosition: number ) => {
			console.log( normalizedPosition );
		},
		// On jumpy scrolls a node may bottom-in then top-out in same loop
		onFastForward: "execute_both" // "skip_both" | "execute_last"
	},
	offset: 10, // increases bounds in pixels
	onRemoveNode: () => element.dataset.ioActive = "0",
	getBounds: () => {
		const { top, bottom } = element.getBoundingClientRect();
		return { 
			start: top + window.scrollY, 
			end: bottom + window.scrollY 
		};
	},
});

TODO

• Refactor to be able to run with horizontal scrolls
• Execute logic for initial in-viewport nodes