fix(merge): Handle edge-case for merge

src/object/merge.spec.ts

@@ -59,6 +59,37 @@ describe('merge', () => {
     expect(result).toEqual({ a: [1, 2, 3] });
   });
 
+  it('should handle merging arrays into non-array target values', () => {
+    const target = { a: 1, b: {} };
+    const numbers = [1, 2, 3];
+    const source = { b: numbers, c: 4 };
+    const result = merge(target, source);
+
+    expect(result).toEqual({ a: 1, b: numbers, c: 4 });
+    expect(result.b).not.toBe(numbers);
+  });
+
+  it('should create new plain object when merged', () => {
+    const plainObject = { b: 2 } as const;
+    const target = {};
+    const source = { a: plainObject };
+    const result = merge(target, source);
+
+    expect(result).toEqual({ a: plainObject });
+    expect(result.a).not.toBe(plainObject);
+  });
+
+  it('should handle merging values that are neither arrays nor plain objects', () => {
+    const date = new Date();
+    const target = {};
+    const source = { a: date };
+    const result = merge(target, source);
+
+    expect(result).toEqual({ a: date });
+    // unlike arrays and plain objects, the original value is used.
+    expect(result.a).toBe(date);
+  });
+
   it('should not overwrite existing values with undefined from source', () => {
     const target = { a: 1, b: 2 };
     const source = { b: undefined, c: 3 };

src/object/merge.ts

@@ -1,4 +1,4 @@
-import { isObjectLike } from '../compat/predicate/isObjectLike.ts';
+import { isPlainObject } from '../predicate/isPlainObject.ts';
 
 /**
  * Merges the properties of the source object into the target object.
@@ -91,9 +91,9 @@ export function merge(target: any, source: any) {
     const targetValue = target[key];
 
     if (Array.isArray(sourceValue)) {
-      target[key] = merge(targetValue ?? [], sourceValue);
-    } else if (isObjectLike(targetValue) && isObjectLike(sourceValue)) {
-      target[key] = merge(targetValue ?? {}, sourceValue);
+      target[key] = merge(Array.isArray(targetValue) ? targetValue : [], sourceValue);
+    } else if (isPlainObject(sourceValue)) {
+      target[key] = merge(isPlainObject(targetValue) ? targetValue : {}, sourceValue);
     } else if (targetValue === undefined || sourceValue !== undefined) {
       target[key] = sourceValue;
     }