From 8ff2691ae8cfa63d97040c1ff0db3cc648f8e941 Mon Sep 17 00:00:00 2001
From: Vladimir Kharlampidi <nolimits4web@gmail.com>
Date: Wed, 2 Feb 2022 12:57:46 +0300
Subject: [PATCH] fix(core): fix slider freeze with enabled observer

fixes #5414
---
 src/core/update/updateSlides.js | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/core/update/updateSlides.js b/src/core/update/updateSlides.js
index 807ed996b..940d02557 100644
--- a/src/core/update/updateSlides.js
+++ b/src/core/update/updateSlides.js
@@ -291,10 +291,12 @@ export default function updateSlides() {
   }
 
   if (!isVirtual && !params.cssMode && (params.effect === 'slide' || params.effect === 'fade')) {
+    const backFaceHiddenClass = `${params.containerModifierClass}backface-hidden`;
+    const hasClassBackfaceClassAdded = swiper.$el.hasClass(backFaceHiddenClass);
     if (slidesLength <= params.maxBackfaceHiddenSlides) {
-      swiper.$el.addClass(`${params.containerModifierClass}backface-hidden`);
-    } else {
-      swiper.$el.removeClass(`${params.containerModifierClass}backface-hidden`);
+      if (!hasClassBackfaceClassAdded) swiper.$el.addClass(backFaceHiddenClass);
+    } else if (hasClassBackfaceClassAdded) {
+      swiper.$el.removeClass(backFaceHiddenClass);
     }
   }
 }