From 0d057e207271bd82546eddd6376db4d7ff414a1d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Csonka=20B=C3=A1lint?= <balint777@gmail.com>
Date: Thu, 13 May 2021 19:32:56 +0200
Subject: [PATCH] Make sure that throwing an exception in an observer does not
 leave the PropertiesChanged mixin in an invalid state

---
 lib/mixins/properties-changed.js | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/lib/mixins/properties-changed.js b/lib/mixins/properties-changed.js
index 9e481d6734..ee2d84224b 100644
--- a/lib/mixins/properties-changed.js
+++ b/lib/mixins/properties-changed.js
@@ -374,16 +374,19 @@ export const PropertiesChanged = dedupingMixin(
      * @override
      */
     _flushProperties() {
-      this.__dataCounter++;
-      const props = this.__data;
-      const changedProps = this.__dataPending;
-      const old = this.__dataOld;
-      if (this._shouldPropertiesChange(props, changedProps, old)) {
-        this.__dataPending = null;
-        this.__dataOld = null;
-        this._propertiesChanged(props, changedProps, old);
+      try {
+        this.__dataCounter++;
+        const props = this.__data;
+        const changedProps = this.__dataPending;
+        const old = this.__dataOld;
+        if (this._shouldPropertiesChange(props, changedProps, old)) {
+          this.__dataPending = null;
+          this.__dataOld = null;
+          this._propertiesChanged(props, changedProps, old);
+        }
+      } finally {
+        this.__dataCounter--;
       }
-      this.__dataCounter--;
     }
 
     /**