fix(deepmerge): should not mutate the input object [#76] (#77)

packages/utils/src/__tests__/deepmerge.test.ts

@@ -6,7 +6,7 @@ describe('deepmerge', () => {
       const mergeObject = { a: { b: 2 } };
       const result = deepmerge({ a: { c: 3 }, b: 2, c: 3 }, mergeObject);
 
-      expect(result).toMatchObject({ a: { b: 2, c: 3 }, b: 2, c: 3 });
+      expect(result).toEqual({ a: { b: 2, c: 3 }, b: 2, c: 3 });
     });
 
     test('should work with empty object', () => {
@@ -27,7 +27,7 @@ describe('deepmerge', () => {
       );
       expect(result).toEqual({
         a: { b: { c: { d: 'change string' } } },
-        b: { a: { d: true } },
+        b: { a: { d: true } }
       });
     });
 
@@ -78,4 +78,14 @@ describe('deepmerge', () => {
       expect(result.a.b.b.c).toBe(true);
     });
   });
+
+  test('should not mutate the input object', () => {
+    const origin = { a: { c: 3 }, b: 2, c: 3 };
+    const target = { a: { b: 2 } };
+    const result = deepmerge(origin, target);
+
+    expect(result).toEqual({ a: { b: 2, c: 3 }, b: 2, c: 3 });
+    expect(origin).toEqual({ a: { c: 3 }, b: 2, c: 3 });
+    expect(target).toEqual({ a: { b: 2 } });
+  });
 });

packages/utils/src/deepmerge.ts

@@ -2,22 +2,23 @@ function mergeTwoObject(origin: any, target: any) {
   if (target === null || typeof target === 'undefined') {
     return origin;
   }
+  const result = { ...origin };
 
-  Object.keys(target).forEach((key) => {
-    const originValue = origin[key];
+  Object.keys(target).forEach(key => {
+    const originValue = result[key];
     const targetValue = target[key];
     if (Array.isArray(originValue) || Array.isArray(targetValue)) {
-      origin[key] = targetValue;
+      result[key] = targetValue;
     } else if (
       typeof originValue === 'object' &&
       typeof targetValue === 'object'
     ) {
-      origin[key] = mergeTwoObject(originValue, targetValue);
+      result[key] = mergeTwoObject(originValue, targetValue);
     } else {
-      origin[key] = targetValue;
+      result[key] = targetValue;
     }
   });
-  return origin;
+  return result;
 }
 
 export function deepmerge(...args: any[]) {