From 9623c1cc4263f439081d057a79c1d27ebab198fb Mon Sep 17 00:00:00 2001
From: Sumit Asthana <asthana.sumit23@gmail.com>
Date: Sat, 5 Dec 2015 23:14:15 +0530
Subject: [PATCH] RelatedArticles load after half window scroll

Only triggers RelatedArticles module load and query after user has scrolled
through half the document height.

Bug: T116838
Change-Id: If290988fb7cc187cad37dd4a8a2c4f38abed9bb9
---
 extension.json                                |  3 +-
 .../index.js                                  | 42 +++++++++++++------
 2 files changed, 32 insertions(+), 13 deletions(-)

diff --git a/extension.json b/extension.json
index f1f11684..9917e582 100644
--- a/extension.json
+++ b/extension.json
@@ -88,7 +88,8 @@
 			],
 			"dependencies": [
 				"mediawiki.api",
-				"ext.relatedArticles.readMore.gateway"
+				"ext.relatedArticles.readMore.gateway",
+				"jquery.throttle-debounce"
 			],
 			"targets": [
 				"mobile",
diff --git a/resources/ext.relatedArticles.readMore.bootstrap/index.js b/resources/ext.relatedArticles.readMore.bootstrap/index.js
index 3cd056e3..bf0af833 100644
--- a/resources/ext.relatedArticles.readMore.bootstrap/index.js
+++ b/resources/ext.relatedArticles.readMore.bootstrap/index.js
@@ -8,25 +8,43 @@
 			mw.config.get( 'wgRelatedArticlesUseCirrusSearch' ),
 			mw.config.get( 'wgRelatedArticlesOnlyUseCirrusSearch' )
 		),
-		LIMIT = 3;
+		LIMIT = 3,
+		debouncedLoad = $.debounce( 100, function () {
+			loadRelatedArticles();
+		} ),
+		$window = $( window ),
+		/**
+		 * Threshold value to load related articles - after about half scroll
+		 */
+		scrollThreshold = ( $( document ).height() / 2 ) - $window.height();
 
+	function loadRelatedArticles() {
+		if ( $window.scrollTop() > scrollThreshold ) {
+			$.when(
+				// Note we load dependencies here rather than ResourceLoader
+				// to avoid PHP exceptions when Cards not installed
+				// which should never happen given the if statement.
+				mw.loader.using( [ 'ext.cards', 'ext.relatedArticles.readMore' ] ),
+				relatedPages.getForCurrentPage( LIMIT )
+			).done( function ( _, pages ) {
+				if ( pages.length ) {
+					mw.track( 'ext.relatedArticles.init', pages );
+				}
+			} );
+			// detach handler to stop subsequent loads on scroll
+			$window.off( 'scroll', debouncedLoad );
+		}
+	}
 	if (
 		config.wgNamespaceNumber === 0 &&
 		!config.wgIsMainPage &&
 		// any skin except minerva stable
 		( config.skin !== 'minerva' || config.wgMFMode === 'beta' )
 	) {
-		$.when(
-			// Note we load dependencies here rather than ResourceLoader
-			// to avoid PHP exceptions when Cards not installed
-			// which should never happen given the if statement.
-			mw.loader.using( [ 'ext.cards', 'ext.relatedArticles.readMore' ] ),
-			relatedPages.getForCurrentPage( LIMIT )
-		).done( function ( _, pages ) {
-			if ( pages.length ) {
-				mw.track( 'ext.relatedArticles.init', pages );
-			}
-		} );
+		// try related articles load on scroll
+		$window.on( 'scroll', debouncedLoad );
+		// try an initial load, in case of no scroll
+		loadRelatedArticles();
 	}
 
 }( jQuery ) );