From e266acc3e8a3f887ecfdc0d350ceffa0e2fb2716 Mon Sep 17 00:00:00 2001
From: Mark Amery <markrobertamery@gmail.com>
Date: Wed, 12 Aug 2026 14:41:12 +0100
Subject: [PATCH 1/4] Add test showing behaviour reported in
 https://github.com/kpdecker/jsdiff/issues/699

---
 test/diff/json.js | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/test/diff/json.js b/test/diff/json.js
index 7c744cb0..d7f2de7c 100644
--- a/test/diff/json.js
+++ b/test/diff/json.js
@@ -127,6 +127,38 @@ describe('diff/json', function() {
         { count: 1, value: '}', removed: false, added: false }
       ]);
     });
+
+    it('handles custom toJSON methods like JSON.stringify does', function() {
+      const x = {
+        toJSON: () => 'aaa'
+      };
+      const y = {
+        toJSON: () => 'bbb'
+      };
+
+      expect(diffJson({ foo: x }, {foo: y})).to.eql([
+        { count: 1, value: '{\n', removed: false, added: false },
+        { count: 1, value: '  "foo": "aaa"\n', added: false, removed: true },
+        { count: 1, value: '  "foo": "bbb"\n', added: true, removed: false },
+        { count: 1, value: '}', removed: false, added: false }
+      ]);
+    });
+
+    it('treats non-callable toJSON properties as normal properties (like JSON.stringify does)', function() {
+      const x = {
+        toJSON: 'aaa'
+      };
+      const y = {
+        toJSON: 'bbb'
+      };
+
+      expect(diffJson(x, y)).to.eql([
+        { count: 1, value: '{\n', removed: false, added: false },
+        { count: 1, value: '  "toJSON": "aaa"\n', added: false, removed: true },
+        { count: 1, value: '  "toJSON": "bbb"\n', added: true, removed: false },
+        { count: 1, value: '}', removed: false, added: false }
+      ]);
+    });
   });
 
   describe('#canonicalize', function() {

From c0d740450c6477d522df0bc4d0e54144adc1a7a6 Mon Sep 17 00:00:00 2001
From: Mark Amery <markrobertamery@gmail.com>
Date: Wed, 12 Aug 2026 14:44:25 +0100
Subject: [PATCH 2/4] Fix https://github.com/kpdecker/jsdiff/issues/699

---
 src/diff/json.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/diff/json.ts b/src/diff/json.ts
index 20fe8c84..f0207779 100644
--- a/src/diff/json.ts
+++ b/src/diff/json.ts
@@ -97,7 +97,7 @@ export function canonicalize(
     return canonicalizedObj;
   }
 
-  if (obj && obj.toJSON) {
+  if (obj && typeof obj.toJSON === 'function') {
     obj = obj.toJSON();
   }
 

From 24b545706018ca931285d5c9cd62cbe5239a5ae3 Mon Sep 17 00:00:00 2001
From: Mark Amery <markrobertamery@gmail.com>
Date: Wed, 12 Aug 2026 14:49:45 +0100
Subject: [PATCH 3/4] Add release notes

---
 release-notes.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/release-notes.md b/release-notes.md
index 64ddbf75..47410e70 100644
--- a/release-notes.md
+++ b/release-notes.md
@@ -3,6 +3,7 @@
 ## 9.1.0 (prerelease)
 
 - [#697](https://github.com/kpdecker/jsdiff/pull/697) *`diffJson` now correctly handles JSON objects containing a key named `__proto__`*. (Previously, the returned diff would be as if the `__proto__` key did not exist on either of the objects being diffed.)
+- [#700](https://github.com/kpdecker/jsdiff/pull/700) *`diffJson` now correctly handles JSON objects containing a non-callable property named `toJSON`* - i.e. it gives such a property no special behaviour whatsoever, just as `JSON.stringify` doesn't. (*Callable* `toJSON` properties continue to get the same special behaviour that `JSON.stringify` gives them.)
 
 ## 9.0.0
 

From a6730b83d1b277b8df6fee7b6fe3bcf9cbf30cbc Mon Sep 17 00:00:00 2001
From: Mark Amery <markrobertamery@gmail.com>
Date: Wed, 12 Aug 2026 14:50:18 +0100
Subject: [PATCH 4/4] Release notes

---
 release-notes.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/release-notes.md b/release-notes.md
index 47410e70..c3d1df85 100644
--- a/release-notes.md
+++ b/release-notes.md
@@ -3,7 +3,7 @@
 ## 9.1.0 (prerelease)
 
 - [#697](https://github.com/kpdecker/jsdiff/pull/697) *`diffJson` now correctly handles JSON objects containing a key named `__proto__`*. (Previously, the returned diff would be as if the `__proto__` key did not exist on either of the objects being diffed.)
-- [#700](https://github.com/kpdecker/jsdiff/pull/700) *`diffJson` now correctly handles JSON objects containing a non-callable property named `toJSON`* - i.e. it gives such a property no special behaviour whatsoever, just as `JSON.stringify` doesn't. (*Callable* `toJSON` properties continue to get the same special behaviour that `JSON.stringify` gives them.)
+- [#700](https://github.com/kpdecker/jsdiff/pull/700) *`diffJson` now correctly handles JSON objects containing a non-callable property named `toJSON`* - i.e. it gives such a property no special behaviour whatsoever, just as `JSON.stringify` doesn't. Previously, such properties caused an error to be thrown. (*Callable* `toJSON` properties continue to get the same special behaviour that `JSON.stringify` gives them.)
 
 ## 9.0.0