From 7ce7a9f5828bc4581b3b71dd4747f8f06f508ae6 Mon Sep 17 00:00:00 2001
From: Brian Huf <brian.huf@mscsoftware.com>
Date: Tue, 28 Oct 2025 07:05:58 -0700
Subject: [PATCH] support objects with prototypes

---
 src/index.spec.ts | 29 +++++++++++++++++++++++++++++
 src/index.ts      |  2 +-
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/index.spec.ts b/src/index.spec.ts
index 0370039..b112ee9 100644
--- a/src/index.spec.ts
+++ b/src/index.spec.ts
@@ -824,6 +824,35 @@ describe('a generate json patch function', () => {
       expect(patch).to.eql([]);
     });
   });
+
+  describe('with object prototypes', () => {
+    it('handles objects', () => {
+      class MySubObject {
+        c = '';
+        d = 0;
+      }
+
+      class MyObject {
+        a = new MySubObject();
+        b = '';
+
+        method() {
+          return 'hello';
+        }
+      }
+
+      const before = new MyObject();
+      const after = new MyObject();
+      after.b = 'changed';
+      after.a.d = 42;
+
+      const patch = generateJSONPatch(before, after);
+      expect(patch).to.eql([
+        { op: 'replace', path: '/a/d', value: 42 },
+        { op: 'replace', path: '/b', value: 'changed' },
+      ]);
+    });
+  });
 });
 
 function doPatch(json: JsonValue, patch: Patch) {
diff --git a/src/index.ts b/src/index.ts
index 9cc3859..1c5ea51 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -248,7 +248,7 @@ function isPrimitiveValue(value: JsonValue): value is JsonValue {
 }
 
 function isJsonObject(value: JsonValue): value is JsonObject {
-  return value?.constructor === Object;
+  return value !== null && typeof value === 'object' && !Array.isArray(value);
 }
 
 function deepEqual(objA: any, objB: any) {