From 9c1a713c6e6f9afb6ce1e078a80ec1a124def540 Mon Sep 17 00:00:00 2001
From: Daniel Waterworth <me@danielwaterworth.com>
Date: Thu, 7 Nov 2019 09:46:00 +0000
Subject: [PATCH] FIX: The internal position on the topic timeline is a scroll
 position

... instead of a post index. This is so that updatePosition is called
when switching between the last two scroll positions.
---
 .../discourse/widgets/topic-timeline.js.es6          | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/app/assets/javascripts/discourse/widgets/topic-timeline.js.es6 b/app/assets/javascripts/discourse/widgets/topic-timeline.js.es6
index 36db3959ba2..a43e9fca544 100644
--- a/app/assets/javascripts/discourse/widgets/topic-timeline.js.es6
+++ b/app/assets/javascripts/discourse/widgets/topic-timeline.js.es6
@@ -187,8 +187,11 @@ createWidget("timeline-scrollarea", {
     }
 
     if (this.state.position !== result.scrollPosition) {
-      this.state.position = result.scrollPosition;
-      this.sendWidgetAction("updatePosition", current);
+      this.sendWidgetAction(
+        "updatePosition",
+        result.current,
+        result.scrollPosition
+      );
     }
 
     return result;
@@ -387,7 +390,7 @@ export default createWidget("topic-timeline", {
     return { position: null, excerpt: null };
   },
 
-  updatePosition(scrollPosition) {
+  updatePosition(postIdx, scrollPosition) {
     if (!this.attrs.fullScreen) {
       return;
     }
@@ -403,7 +406,8 @@ export default createWidget("topic-timeline", {
       }
 
       // we have an off by one, stream is zero based,
-      stream.excerpt(scrollPosition - 1).then(info => {
+      // postIdx is 1 based
+      stream.excerpt(postIdx - 1).then(info => {
         if (info && this.state.position === scrollPosition) {
           let excerpt = "";