Fix deep merge of nested DOM elements

jest.config.js

@@ -1,5 +1,5 @@
 export default {
-    testEnvironment: 'node',
+    testEnvironment: 'jsdom',
     transform: {
         '^.+\\.jsx?$': 'babel-jest', // Use Babel to transpile ES modules
     },

package.json

@@ -1,14 +1,15 @@
 {
     "name": "@webfactoryde/merge-objects",
-    "version": "1.0.0",
+    "version": "1.0.1",
     "description": "JS Utility that merges multiple objects into one, with an option for deep merging",
     "main": "src/merge-objects.js",
     "type": "module",
     "devDependencies": {
         "@babel/core": "^7.28.3",
         "@babel/preset-env": "^7.28.3",
         "babel-jest": "^30.1.1",
-        "jest": "^30.1.0"
+        "jest": "^30.1.0",
+        "jest-environment-jsdom": "^30.2.0"
     },
     "scripts": {
         "test": "jest"

src/merge-objects.js

@@ -32,7 +32,7 @@ export default function mergeObjects(...args) {
     const merge = (obj) => {
         for (const prop in obj) {
             if (Object.prototype.hasOwnProperty.call(obj, prop)) {
-                if (deep && typeof obj[prop] === 'object' && obj[prop] !== null) {
+                if (deep && Object.prototype.toString.call(obj[prop]) === '[object Object]') {
                     extended[prop] = mergeObjects(true, extended[prop] || {}, obj[prop]);
                 } else {
                     extended[prop] = obj[prop];

tests/mergeObjects.test.js

@@ -37,10 +37,11 @@ describe('mergeObjects', () => {
     });
 
     test('should handle empty objects', () => {
-        const obj1 = {};
+        const obj1 = { a: 1 };
         const obj2 = {};
-        const result = mergeObjects(false, obj1, obj2);
-        expect(result).toEqual({});
+        const obj3 = { c: 3 };
+        const result = mergeObjects(false, obj1, obj2, obj3);
+        expect(result).toEqual({ a: 1, c: 3 });
     });
 
     test('should handle deep merge with empty objects', () => {
@@ -49,4 +50,16 @@ describe('mergeObjects', () => {
         const result = mergeObjects(true, obj1, obj2);
         expect(result).toEqual({ a: 1, b: { y: 30 }, c: 4 });
     });
+
+    test('should preserve DOM element references in deep merge', () => {
+        const div = document.createElement('div');
+        div.id = 'test';
+
+        const obj1 = {};
+        const obj2 = { element: div };
+        const result = mergeObjects(true, obj1, obj2);
+
+        expect(result.element).toBe(div);
+        expect(result.element.id).toBe('test');
+    });
 });