From eb0e304ff8e47b226713df6072dc87d58da89004 Mon Sep 17 00:00:00 2001
From: Alexander Zinchuk <alx.zinchuk@gmail.com>
Date: Sat, 5 Mar 2022 18:06:23 +0100
Subject: [PATCH] [Debug] Teact: Assert when cached virtual element was moved
 within tree

---
 src/lib/teact/teact-dom.ts | 7 +++++++
 src/lib/teact/teact.ts     | 3 ++-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/lib/teact/teact-dom.ts b/src/lib/teact/teact-dom.ts
index c82b3c80..065027c0 100644
--- a/src/lib/teact/teact-dom.ts
+++ b/src/lib/teact/teact-dom.ts
@@ -98,6 +98,13 @@ function renderWithVirtual(
     return $new;
   }
 
+  if (DEBUG && $new) {
+    const newTarget = getTarget($new);
+    if (newTarget && (!$current || newTarget !== getTarget($current))) {
+      throw new Error('[Teact] Cached virtual element was moved within tree');
+    }
+  }
+
   if (!$current && $new) {
     if (isNewComponent) {
       $new = initComponent($new as VirtualElementComponent, $parent, index, parentEl);
diff --git a/src/lib/teact/teact.ts b/src/lib/teact/teact.ts
index 2e61bf2c..a42ea8f8 100644
--- a/src/lib/teact/teact.ts
+++ b/src/lib/teact/teact.ts
@@ -449,7 +449,8 @@ function forceUpdateComponent(componentInstance: ComponentInstance) {
 
 export function getTarget($element: VirtualElement): Node | undefined {
   if (isComponentElement($element)) {
-    return getTarget($element.children[0]);
+    const componentElement = $element.children[0];
+    return componentElement ? getTarget(componentElement) : undefined;
   } else {
     return $element.target;
   }