Update scroll observer to allow event logging

- Permits logging for scroll events without sticky header.
- Update function name to be more precise.

Bug: T292586
Change-Id: I441b4bf81bc4a36a03f0f1c215d86b01dce2911d

resources/skins.vector.es6/main.js

@@ -26,15 +26,9 @@ const main = () => {
 		// Note that the default test group is set to experience the feature by default.
 		// @ts-ignore
 		testGroup = stickyConfig ? stickyConfig.group : scrollObserver.FEATURE_TEST_GROUP,
-		targetElement = stickyHeader.header;
-
-	// Check for target html, sticky header conditionals, and test group to continue.
-	if ( !( targetElement &&
-		stickyHeader.isStickyHeaderAllowed() &&
-		testGroup !== 'unsampled' )
-	) {
-		return;
-	}
+		targetElement = stickyHeader.header,
+		targetIntersection = stickyHeader.stickyIntersection,
+		isStickyHeaderAllowed = stickyHeader.isStickyHeaderAllowed() && testGroup !== 'unsampled';
 
 	// Fire the A/B test enrollment hook.
 	AB.initAB( testGroup );
@@ -43,17 +37,25 @@ const main = () => {
 	// for event logging if AB test is enabled.
 	const observer = scrollObserver.initScrollObserver(
 		() => {
-			scrollObserver.onShowFeature( targetElement, testGroup );
-			scrollObserver.logScrollEvent( 'down' );
+			if ( targetElement && isStickyHeaderAllowed ) {
+				scrollObserver.onShowFeature( targetElement, testGroup );
+			}
+			scrollObserver.fireScrollHook( 'down' );
 		},
 		() => {
-			scrollObserver.onHideFeature( targetElement, testGroup );
-			scrollObserver.logScrollEvent( 'up' );
+			if ( targetElement && isStickyHeaderAllowed ) {
+				scrollObserver.onHideFeature( targetElement, testGroup );
+			}
+			scrollObserver.fireScrollHook( 'up' );
 		}
 
 	);
 
-	stickyHeader.initStickyHeader( observer );
+	if ( isStickyHeaderAllowed ) {
+		stickyHeader.initStickyHeader( observer );
+	} else if ( targetIntersection ) {
+		observer.observe( targetIntersection );
+	}
 };
 
 module.exports = {

resources/skins.vector.es6/scrollObserver.js

@@ -48,7 +48,7 @@ function onHideFeature( element, group ) {
  *
  * @param {string} direction the scroll direction
  */
-function logScrollEvent( direction ) {
+function fireScrollHook( direction ) {
 	if ( direction === 'down' ) {
 		// @ts-ignore
 		mw.hook( SCROLL_HOOK ).fire( { context: SCROLL_CONTEXT_BELOW } );
@@ -85,6 +85,6 @@ module.exports = {
 	initScrollObserver,
 	onShowFeature,
 	onHideFeature,
-	logScrollEvent,
+	fireScrollHook,
 	FEATURE_TEST_GROUP
 };

resources/skins.vector.es6/stickyHeader.js

@@ -427,5 +427,6 @@ module.exports = {
 	initStickyHeader,
 	isStickyHeaderAllowed,
 	header,
+	stickyIntersection,
 	STICKY_HEADER_EXPERIMENT_NAME
 };