From cf4d66b28024bd6146de819c52bd2c38319caf34 Mon Sep 17 00:00:00 2001
From: Dan Abramov <dan.abramov@gmail.com>
Date: Sat, 10 Sep 2022 07:16:18 +0100
Subject: [PATCH] [Beta] Guard against a crash

---
 beta/src/components/MDX/Sandpack/NavigationBar.tsx | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/beta/src/components/MDX/Sandpack/NavigationBar.tsx b/beta/src/components/MDX/Sandpack/NavigationBar.tsx
index 922982d6..ff7ac23d 100644
--- a/beta/src/components/MDX/Sandpack/NavigationBar.tsx
+++ b/beta/src/components/MDX/Sandpack/NavigationBar.tsx
@@ -53,7 +53,11 @@ export function NavigationBar({providedFiles}: {providedFiles: Array<string>}) {
       hasJustToggledDropdown.current = false;
       return;
     }
-    const tabsWidth = tabsRef.current!.getBoundingClientRect().width;
+    if (tabsRef.current === null) {
+      // Some ResizeObserver calls come after unmount.
+      return;
+    }
+    const tabsWidth = tabsRef.current.getBoundingClientRect().width;
     const needsDropdown = tabsWidth >= containerWidth;
     if (needsDropdown !== showDropdown) {
       hasJustToggledDropdown.current = true;