From 610597530867e10fb91baf85d65cadf6c38c214a Mon Sep 17 00:00:00 2001
From: Daniel Imms <daimms@microsoft.com>
Date: Thu, 1 Feb 2018 10:24:17 -0800
Subject: [PATCH] Ensure viewport is attached before syncing scrollbar

Fixes #1265
---
 src/Viewport.ts | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/Viewport.ts b/src/Viewport.ts
index 87ecd69e..59dc304d 100644
--- a/src/Viewport.ts
+++ b/src/Viewport.ts
@@ -93,6 +93,12 @@ export class Viewport implements IViewport {
    * @param ev The scroll event.
    */
   private onScroll(ev: Event): void {
+    // Don't attempt to scroll if the element is not visible, otherwise scrollTop will be corrupt
+    // which causes the terminal to scroll the buffer to the top
+    if (!this.viewportElement.offsetParent) {
+      return;
+    }
+
     const newRow = Math.round(this.viewportElement.scrollTop / this.currentRowHeight);
     const diff = newRow - this.terminal.buffer.ydisp;
     this.terminal.scrollLines(diff, true);