From 9cfafc30b569ddca0916199df43f0b804a4b0a0d Mon Sep 17 00:00:00 2001
From: Pierre Paridans <pierre@paridans.org>
Date: Tue, 6 Jul 2021 10:39:51 +0200
Subject: [PATCH] [IMP] vdom: performance improvement

Port from original snabbdom project: snabbdom/snabbdom#634

The issue is that before this commit, the removeClass method was
sometimes called even if it is not useful. See this comment for more
detail: https://github.com/snabbdom/snabbdom/issues/633#issue-618706258
---
 src/vdom/modules.ts | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/vdom/modules.ts b/src/vdom/modules.ts
index 413e9f24..27535492 100644
--- a/src/vdom/modules.ts
+++ b/src/vdom/modules.ts
@@ -231,7 +231,8 @@ function updateClass(oldVnode: VNode, vnode: VNode): void {
   elm = vnode.elm as Element;
 
   for (name in oldClass) {
-    if (name && !klass[name]) {
+    if (name && !klass[name] && !Object.prototype.hasOwnProperty.call(klass, name)) {
+      // was `true` and now not provided
       elm.classList.remove(name);
     }
   }