From 2e860eddc12289bc18417e309c8d53fe206fb457 Mon Sep 17 00:00:00 2001
From: Guo Xiang Tan <tgx_world@hotmail.com>
Date: Fri, 1 Dec 2017 17:07:28 +0800
Subject: [PATCH] Don't sync scroll when input is not scrollable.

https://meta.discourse.org/t/composer-preview-scroll-not-syncing-with-editor/74975/14?u=tgxworld
---
 .../javascripts/discourse/components/composer-editor.js.es6 | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/app/assets/javascripts/discourse/components/composer-editor.js.es6 b/app/assets/javascripts/discourse/components/composer-editor.js.es6
index 4b95913aa45..1d715a396de 100644
--- a/app/assets/javascripts/discourse/components/composer-editor.js.es6
+++ b/app/assets/javascripts/discourse/components/composer-editor.js.es6
@@ -254,8 +254,12 @@ export default Ember.Component.extend({
 
   _syncEditorAndPreviewScroll($input, $preview, scrollMap) {
     let scrollTop;
+    const inputHeight = $input.height();
+    const inputScrollHeight = $input[0].scrollHeight;
+    const inputClientHeight = $input[0].clientHeight;
+    const scrollable = inputScrollHeight > inputClientHeight;
 
-    if (($input.height() + $input.scrollTop() + 100) > $input[0].scrollHeight) {
+    if (scrollable && ((inputHeight + $input.scrollTop() + 100) > inputScrollHeight)) {
       scrollTop = $preview[0].scrollHeight;
     } else {
       const lineHeight = parseFloat($input.css('line-height'));