feat(homepage-posts): infinite scroll

src/blocks/homepage-articles/block.json

@@ -18,6 +18,10 @@
 			"type": "boolean",
 			"default": false
 		},
+		"infiniteScroll": {
+			"type": "boolean",
+			"default": false
+		},
 		"readMoreLabel": {
 			"type": "string",
 			"default": "Keep reading"

src/blocks/homepage-articles/edit.tsx

@@ -280,6 +280,7 @@ class Edit extends Component< HomepageArticlesProps > {
 			mobileStack,
 			minHeight,
 			moreButton,
+			infiniteScroll,
 			showExcerpt,
 			showReadMore,
 			readMoreLabel,
@@ -434,11 +435,20 @@ class Edit extends Component< HomepageArticlesProps > {
 						</i>
 					) : (
 						! specificMode && (
-							<ToggleControl
-								label={ __( 'Show "Load more posts" Button', 'newspack-blocks' ) }
-								checked={ moreButton }
-								onChange={ () => setAttributes( { moreButton: ! moreButton } ) }
-							/>
+							<>
+								<ToggleControl
+									label={ __( 'Show "Load more posts" Button', 'newspack-blocks' ) }
+									checked={ moreButton }
+									onChange={ () => setAttributes( { moreButton: ! moreButton } ) }
+								/>
+								{ moreButton && (
+									<ToggleControl
+										label={ __( 'Infinite Scroll', 'newspack-blocks' ) }
+										checked={ infiniteScroll }
+										onChange={ () => setAttributes( { infiniteScroll: ! infiniteScroll } ) }
+									/>
+								) }
+							</>
 						)
 					) }
 					<ToggleControl

src/blocks/homepage-articles/view.js

@@ -35,18 +35,27 @@ function buildLoadMoreHandler( blockWrapperEl ) {
 		return;
 	}
 	const postsContainerEl = blockWrapperEl.querySelector( '[data-posts]' );
+	const isInfiniteScroll = btnEl.getAttribute( 'data-infinite-scroll' );
 
 	// Set initial state flags.
-	let isFetching = false;
+	window.newspackBlocksIsFetching = window.newspackBlocksIsFetching || false;
+	window.newspackBlocksFetchQueue = window.newspackBlocksFetchQueue || [];
 	let isEndOfData = false;
+	let isPending = false;
 
-	btnEl.addEventListener( 'click', () => {
-		// Early return if still fetching or no more posts to render.
-		if ( isFetching || isEndOfData ) {
-			return false;
+	const maybeLoadMore = () => {
+		if ( isPending ) {
+			return;
 		}
+		isPending = true;
+		loadMore();
+	};
 
-		isFetching = true;
+	const loadMore = () => {
+		// Early return if no more posts to render.
+		if ( isEndOfData ) {
+			return false;
+		}
 
 		blockWrapperEl.classList.remove( 'is-error' );
 		blockWrapperEl.classList.add( 'is-loading' );
@@ -55,48 +64,86 @@ function buildLoadMoreHandler( blockWrapperEl ) {
 		const requestURL =
 			btnEl.getAttribute( 'data-next' ) + '&exclude_ids=' + getRenderedPostsIds().join( ',' );
 
+		// If there's already a fetch in progress, queue this one to run after it ends.
+		if ( window.newspackBlocksIsFetching ) {
+			window.newspackBlocksFetchQueue.push( loadMore );
+			return false;
+		}
+
+		window.newspackBlocksIsFetching = true;
 		fetchWithRetry( { url: requestURL, onSuccess, onError }, fetchRetryCount );
+	};
 
-		/**
-		 * @param {Object} data Post data
-		 */
-		function onSuccess( data ) {
-			// Validate received data.
-			if ( ! isPostsDataValid( data ) ) {
-				return onError();
-			}
+	/**
+	 * @param {Object} data Post data
+	 */
+	function onSuccess( data ) {
+		// Validate received data.
+		if ( ! isPostsDataValid( data ) ) {
+			return onError();
+		}
 
-			if ( data.items.length ) {
-				// Render posts' HTML from string.
-				const postsHTML = data.items.map( item => item.html ).join( '' );
-				postsContainerEl.insertAdjacentHTML( 'beforeend', postsHTML );
-			}
+		if ( data.items.length ) {
+			// Render posts' HTML from string.
+			const postsHTML = data.items.map( item => item.html ).join( '' );
+			postsContainerEl.insertAdjacentHTML( 'beforeend', postsHTML );
+		}
 
-			if ( data.next ) {
-				// Save next URL as button's attribute.
-				btnEl.setAttribute( 'data-next', data.next );
-			}
+		if ( data.next ) {
+			// Save next URL as button's attribute.
+			btnEl.setAttribute( 'data-next', data.next );
+		}
 
-			if ( ! data.items.length || ! data.next ) {
-				isEndOfData = true;
-				blockWrapperEl.classList.remove( 'has-more-button' );
-			}
+		if ( ! data.items.length || ! data.next ) {
+			isEndOfData = true;
+			blockWrapperEl.classList.remove( 'has-more-button' );
+		}
 
-			isFetching = false;
+		onEnd();
+	}
 
-			blockWrapperEl.classList.remove( 'is-loading' );
-		}
+	/**
+	 * Handle fetching error
+	 */
+	function onError() {
+		blockWrapperEl.classList.add( 'is-error' );
+		onEnd();
+	}
 
-		/**
-		 * Handle fetching error
-		 */
-		function onError() {
-			isFetching = false;
+	/**
+	 * Callback to run after a fetch request is completed.
+	 */
+	function onEnd() {
+		window.newspackBlocksIsFetching = false;
+		blockWrapperEl.classList.remove( 'is-loading' );
 
-			blockWrapperEl.classList.remove( 'is-loading' );
-			blockWrapperEl.classList.add( 'is-error' );
+		// If there are queued fetches, run the next one.
+		if ( window.newspackBlocksFetchQueue.length ) {
+			window.newspackBlocksFetchQueue.shift()();
 		}
-	} );
+		isPending = false;
+	}
+
+	btnEl.addEventListener( 'click', maybeLoadMore );
+
+	if ( isInfiniteScroll ) {
+		// Create an intersection observer instance
+		const btnObserver = new IntersectionObserver(
+			entries => {
+				entries.forEach( entry => {
+					if ( entry.isIntersecting ) {
+						maybeLoadMore();
+					}
+				} );
+			},
+			{
+				root: null,
+				rootMargin: '0px',
+				threshold: 1,
+			}
+		);
+		btnObserver.observe( btnEl );
+	}
 }
 
 /**

src/blocks/homepage-articles/view.php

@@ -383,8 +383,12 @@ class="<?php echo esc_attr( $classes ); ?>"
 		<?php
 
 		if ( $has_more_button ) :
+			$load_more = '';
+			if ( (bool) $attributes['infiniteScroll'] ) {
+				$load_more = 'data-infinite-scroll="true"';
+			}
 			?>
-			<button type="button" class="wp-block-button__link" data-next="<?php echo esc_url( $articles_rest_url ); ?>">
+			<button type="button" class="wp-block-button__link" <?php echo esc_attr( $load_more ); ?> data-next="<?php echo esc_url( $articles_rest_url ); ?>">
 				<span class="label">
 					<?php
 					if ( ! empty( $attributes['moreButtonText'] ) ) {

src/types/index.d.ts

@@ -125,6 +125,7 @@ declare global {
 		imageShape: string;
 		minHeight: integer;
 		moreButton: boolean;
+		infiniteScroll: boolean;
 		moreButtonText: string;
 		showAuthor: boolean;
 		showAvatar: boolean;