From 016e9513f87e835adf052fb2f1389ed0d65c43a3 Mon Sep 17 00:00:00 2001
From: Ross <xkjq@ymail.com>
Date: Tue, 2 Mar 2021 19:00:55 +0000
Subject: [PATCH] .

---
 js/viewer.js | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/js/viewer.js b/js/viewer.js
index 19d59a7..fb46d44 100644
--- a/js/viewer.js
+++ b/js/viewer.js
@@ -201,6 +201,10 @@ export function manualScrollDicom(n) {
   // There must be a better way to do this...
   let dicom_element = document.getElementById("dicom-image");
   let c = cornerstone.getEnabledElement(dicom_element);
+
+  // Cancel if no active element
+  if (el == undefined) { return }
+
   let max = c.toolStateManager.toolState.stack.data[0].imageIds.length;
 
   if (max < 2) {