From eccfa1317a11c2abf42a2eb83292253a7e161dd1 Mon Sep 17 00:00:00 2001
From: Robin Ward <robin.ward@gmail.com>
Date: Fri, 3 Jun 2016 17:57:52 -0400
Subject: [PATCH] FIX: Safer offset checking

---
 .../javascripts/discourse/components/topic-timeline.js.es6  | 4 +++-
 app/assets/javascripts/discourse/mixins/docking.js.es6      | 6 +++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/app/assets/javascripts/discourse/components/topic-timeline.js.es6 b/app/assets/javascripts/discourse/components/topic-timeline.js.es6
index 5574e2e06f3..d3b2f648a47 100644
--- a/app/assets/javascripts/discourse/components/topic-timeline.js.es6
+++ b/app/assets/javascripts/discourse/components/topic-timeline.js.es6
@@ -24,7 +24,9 @@ export default MountWidget.extend(Docking, {
   },
 
   dockCheck(info) {
-    const topicTop = $('.container.posts').offset().top - $('#main').offset().top;
+    const mainOffset = $('#main').offset();
+    const offsetTop = mainOffset ? mainOffset.top : 0;
+    const topicTop = $('.container.posts').offset().top - offsetTop;
     const topicBottom = $('#topic-bottom').offset().top;
     const $timeline = this.$('.timeline-container');
     const timelineHeight = $timeline.height() || 400;
diff --git a/app/assets/javascripts/discourse/mixins/docking.js.es6 b/app/assets/javascripts/discourse/mixins/docking.js.es6
index 8e73c1d3e6e..4b2505b1518 100644
--- a/app/assets/javascripts/discourse/mixins/docking.js.es6
+++ b/app/assets/javascripts/discourse/mixins/docking.js.es6
@@ -1,5 +1,9 @@
 const helper = {
-  offset: () => (window.pageYOffset || $('html').scrollTop()) - $('#main').offset().top
+  offset() {
+    const mainOffset = $('#main').offset();
+    const offsetTop = mainOffset ? mainOffset.top : 0;
+    return (window.pageYOffset || $('html').scrollTop()) - offsetTop;
+  }
 };
 
 export default Ember.Mixin.create({