Fix mergeDeepRight function not properly merging objects if key exist…

…s in target with value undefined

CHANGELOG.md

@@ -4,6 +4,23 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/), and this project adheres to [Semantic Versioning](https://semver.org).
 
+## [1.0.3] - 2023-12-18
+### Added
+* *Nothing*
+
+### Changed
+* *Nothing*
+
+### Deprecated
+* *Nothing*
+
+### Removed
+* *Nothing*
+
+### Fixed
+* Fix `mergeDeepRight` function not properly merging objects if key exists in target with value `undefined`.
+
+
 ## [1.0.2] - 2023-11-26
 ### Added
 * *Nothing*

src/merge-deep-right/index.ts

@@ -11,7 +11,9 @@ export const mergeDeepRight = <T extends Record<string, any>>(target: T, source:
 
   Object.keys(source).forEach((key: keyof T) => {
     if (isObject(source[key])) {
-      output[key] = key in target ? mergeDeepRight(target[key], source[key]) : { ...source[key] };
+      output[key] = key in target && target[key] !== undefined
+        ? mergeDeepRight(target[key], source[key])
+        : { ...source[key] };
     } else {
       output[key] = source[key];
     }

src/merge-deep-right/test.ts

@@ -32,6 +32,20 @@ describe('mergeDeepRight', () => {
         something: 'hi!',
       },
     ],
+    [
+      { foo: undefined },
+      {
+        foo: { one: 1, two: 2 },
+      },
+      {
+        foo: { one: 1, two: 2 },
+      },
+    ],
+    [
+      { foo: undefined },
+      { foo: 'something' },
+      { foo: 'something' },
+    ],
   ])('returns expected result', (target, source, expected) => {
     expect(mergeDeepRight(target, source)).toEqual(expected);
   });