From b919bb02b7c1e676f58f81af140b69313d5d2d3f Mon Sep 17 00:00:00 2001
From: "Davide P. Cervone" <dpvc@union.edu>
Date: Wed, 10 Sep 2025 12:35:02 -0400
Subject: [PATCH 1/2] Provide hasOwn polyfill configuration option.

---
 components/mjs/startup/hasown.js | 10 ++++++++++
 components/mjs/startup/init.js   |  1 +
 ts/components/startup.ts         |  1 +
 3 files changed, 12 insertions(+)
 create mode 100644 components/mjs/startup/hasown.js

diff --git a/components/mjs/startup/hasown.js b/components/mjs/startup/hasown.js
new file mode 100644
index 000000000..b886b536b
--- /dev/null
+++ b/components/mjs/startup/hasown.js
@@ -0,0 +1,10 @@
+import {MathJax} from '#js/components/global.js';
+
+if (!Object.hasOwn && MathJax.config.startup.polyfillHasOwn) {
+  Object.hasOwn = function (el, prop) {
+    if (typeof el === 'undefined' || el === null) {
+      throw new TypeError('Cannot convert undefined or null to object');
+    }
+    return Object.prototype.hasOwnProperty.call(Object(el), prop);
+  }
+}
diff --git a/components/mjs/startup/init.js b/components/mjs/startup/init.js
index f34d29799..8ae46803d 100644
--- a/components/mjs/startup/init.js
+++ b/components/mjs/startup/init.js
@@ -1,3 +1,4 @@
+import './hasown.js';
 import './lib/startup.js';
 
 import {combineDefaults} from '#js/components/global.js';
diff --git a/ts/components/startup.ts b/ts/components/startup.ts
index 777bd5c70..9d19beed2 100644
--- a/ts/components/startup.ts
+++ b/ts/components/startup.ts
@@ -620,6 +620,7 @@ if (typeof MathJax._.startup === 'undefined') {
     typeset: true,
     ready: Startup.defaultReady.bind(Startup),
     pageReady: Startup.defaultPageReady.bind(Startup),
+    polyfillHasOwn: false,
   });
   combineWithMathJax({
     startup: Startup,

From 5651923006c451dbc78826bb628407ad4630e306 Mon Sep 17 00:00:00 2001
From: "Davide P. Cervone" <dpvc@union.edu>
Date: Mon, 15 Sep 2025 08:28:40 -0400
Subject: [PATCH 2/2] Make the polyfill opt-out rather than opt-in

---
 ts/components/startup.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ts/components/startup.ts b/ts/components/startup.ts
index 9d19beed2..49cf0e3bf 100644
--- a/ts/components/startup.ts
+++ b/ts/components/startup.ts
@@ -620,7 +620,7 @@ if (typeof MathJax._.startup === 'undefined') {
     typeset: true,
     ready: Startup.defaultReady.bind(Startup),
     pageReady: Startup.defaultPageReady.bind(Startup),
-    polyfillHasOwn: false,
+    polyfillHasOwn: true,
   });
   combineWithMathJax({
     startup: Startup,