From 85d84a0c40f8a22c3b9dcb136738a17e79be4aa4 Mon Sep 17 00:00:00 2001
From: Sampo Osmonen <sampo.osmonen@meiko.fi>
Date: Mon, 9 Mar 2020 19:37:21 +0200
Subject: [PATCH] Add safeguard to handleTouchMove

---
 src/ol/MapBrowserEventHandler.js | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/ol/MapBrowserEventHandler.js b/src/ol/MapBrowserEventHandler.js
index e19b74e55e..18f5899701 100644
--- a/src/ol/MapBrowserEventHandler.js
+++ b/src/ol/MapBrowserEventHandler.js
@@ -275,7 +275,8 @@ class MapBrowserEventHandler extends EventTarget {
    * @private
    */
   handleTouchMove_(event) {
-    if (this.originalPointerMoveEvent_.defaultPrevented) {
+    // In some environments (such as iOS 12), this handler can get called once before the `originalPointerMoveEvent_` is initialized. This prevents crashes in those situations (but may not work correctly if `originalPointerMoveEvent_` lags behind the current event?).
+    if (this.originalPointerMoveEvent_ && this.originalPointerMoveEvent_.defaultPrevented) {
       event.preventDefault();
     }
   }