fix(cloneDeep): maintain prototype when cloning class instances

benchmarks/performance/cloneDeep.bench.ts

@@ -15,6 +15,9 @@ const obj = {
   object: { a: 1, b: 'es-toolkit' },
   date: new Date(),
   regex: /abc/g,
+  instance: new (class Test {
+    value: 1;
+  })(),
   nested: { a: [1, 2, 3], b: { c: 'es-toolkit' }, d: new Date() },
   nested2: { a: { b: { c: { d: { e: { f: { g: 'es-toolkit' } } } } } } },
 };

src/object/clone.spec.ts

@@ -238,4 +238,28 @@ describe('clone', () => {
     expect(clonedError.message).toBe(error.message);
     expect(clonedError.name).toBe(error.name);
   });
+
+  it('should clone class instance', () => {
+    class CustomClass {
+      value: number;
+
+      constructor(value: number) {
+        this.value = value;
+      }
+
+      getValue() {
+        return this.value;
+      }
+    }
+
+    const instance = new CustomClass(123);
+    const clonedInstance = clone(instance);
+
+    expect(clonedInstance).toEqual(instance);
+    expect(clonedInstance).not.toBe(instance);
+    expect(clonedInstance).toBeInstanceOf(CustomClass);
+
+    expect(clonedInstance.value).toBe(instance.value);
+    expect(clonedInstance.getValue()).toBe(123);
+  });
 });

src/object/cloneDeep.spec.ts

@@ -169,6 +169,7 @@ describe('cloneDeep', () => {
       d,
       c: 2,
     });
+    expect(b.getA()).toEqual({ a: 'es-toolkit' });
   });
 
   //-------------------------------------------------------------------------------------

src/object/cloneDeep.ts

@@ -1,4 +1,5 @@
 import { getSymbols } from '../compat/_internal/getSymbols.ts';
+import { isPrototype } from '../compat/_internal/isPrototype.ts';
 import { isPrimitive } from '../predicate/isPrimitive.ts';
 import { isTypedArray } from '../predicate/isTypedArray.ts';
 
@@ -184,7 +185,9 @@ function cloneDeepImpl<T>(obj: T, stack = new Map<any, any>()): T {
   }
 
   if (typeof obj === 'object' && obj !== null) {
-    const result = {};
+    const result =
+      typeof obj.constructor === 'function' && !isPrototype(obj) ? Object.create(Object.getPrototypeOf(obj)) : {};
+
     stack.set(obj, result);
 
     copyProperties(result, obj, stack);