From 1b663eaa2f6c71552c07e9266ef045adb2bca6cc Mon Sep 17 00:00:00 2001
From: Steve Repsher <steverep@users.noreply.github.com>
Date: Thu, 27 Jun 2024 16:20:36 +0000
Subject: [PATCH] Add fallback feature detection for Array.prototype.findLast

---
 src/html/_js_base.html.template | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/html/_js_base.html.template b/src/html/_js_base.html.template
index 7c94ee3fa672..aaa55cbfdcf0 100644
--- a/src/html/_js_base.html.template
+++ b/src/html/_js_base.html.template
@@ -16,5 +16,9 @@
   ) {
     _ls("/static/polyfills/webcomponents-bundle.js", true);
   }
-  var isModern = <%= modernRegex %>.test(navigator.userAgent);
+  // Modern browsers are detected primarily using the user agent string.
+  // A feature detection which roughly lines up with the modern targets is used
+  // as a fallback to guard against spoofs. It should be updated periodically.
+  var isModern = <%= modernRegex %>.test(navigator.userAgent) &&
+    "findLast" in Array.prototype;
 </script>