Add setUndefined option

README.md

@@ -116,6 +116,25 @@ set(obj, 'foo.bar.fez', 'zzz', { merge: true });
 //=> { foo: { bar: { baz: 'qux', fez: 'zzz' } } }
 ```
 
+### options.setUndefined
+
+Set the value to undefined instead of deleting the property when the value is undefined.
+
+**Type**: `boolean`
+
+**Default**: `false`
+
+**Example**
+
+```js
+console.log(set({foo: 'bar', baz: 'foo'}, 'foo', undefined, { setUndefined:  false }));
+//=> { baz: 'foo' }
+
+console.log(set({foo: 'bar', baz: 'foo'}, 'foo', undefined, { setUndefined:  true }));
+//=> { foo: undefined, baz: 'foo' }
+```
+
+
 ## Benchmarks
 
 Benchmarks were run on a MacBook Pro 2.5 GHz Intel Core i7, 16 GB 1600 MHz DDR3.
@@ -271,18 +290,19 @@ You might also be interested in these projects:
 
 ### Contributors
 
-| **Commits** | **Contributor** |  
-| --- | --- |  
-| 87 | [jonschlinkert](https://github.com/jonschlinkert) |  
-| 4  | [doowb](https://github.com/doowb) |  
-| 2  | [mbelsky](https://github.com/mbelsky) |  
-| 1  | [dkebler](https://github.com/dkebler) |  
-| 1  | [GlennKintscher](https://github.com/GlennKintscher) |  
-| 1  | [petermorlion](https://github.com/petermorlion) |  
-| 1  | [abetomo](https://github.com/abetomo) |  
-| 1  | [zeidoo](https://github.com/zeidoo) |  
-| 1  | [ready-research](https://github.com/ready-research) |  
-| 1  | [wtgtybhertgeghgtwtg](https://github.com/wtgtybhertgeghgtwtg) |  
+| **Commits** | **Contributor** |
+| --- | --- |
+| 87 | [jonschlinkert](https://github.com/jonschlinkert) |
+| 4  | [doowb](https://github.com/doowb) |
+| 2  | [mbelsky](https://github.com/mbelsky) |
+| 1  | [dkebler](https://github.com/dkebler) |
+| 1  | [GlennKintscher](https://github.com/GlennKintscher) |
+| 1  | [petermorlion](https://github.com/petermorlion) |
+| 1  | [abetomo](https://github.com/abetomo) |
+| 1  | [zeidoo](https://github.com/zeidoo) |
+| 1  | [ready-research](https://github.com/ready-research) |
+| 1  | [wtgtybhertgeghgtwtg](https://github.com/wtgtybhertgeghgtwtg) |
+| 1  | [snowbldr](https://github.com/snowbldr) |
 
 ### Author
 
@@ -299,4 +319,4 @@ Released under the [MIT License](LICENSE).
 
 ***
 
-_This file was generated by [verb-generate-readme](https://github.com/verbose/verb-generate-readme), v0.8.0, on September 12, 2021._
+_This file was generated by [verb-generate-readme](https://github.com/verbose/verb-generate-readme), v0.8.0, on September 12, 2021._

index.js

@@ -107,8 +107,8 @@ const split = (input, options) => {
 const assignProp = (obj, prop, value, options) => {
   validateKey(prop);
 
-  // Delete property when "value" is undefined
-  if (value === undefined) {
+  // Delete property when "value" is undefined and setUndefined is falsey
+  if (value === undefined && (!options || !options.setUndefined)) {
     deleteProperty(obj, prop);
 
   } else if (options && options.merge) {

test/test.js

@@ -159,6 +159,29 @@ describe('set-value', () => {
       assert.deepEqual(set({ a: 'a', b: { c: 'd' } }, 'b.c'), { a: 'a', b: {} });
     });
 
+    it('should delete the property undefined when setUndefined is false', () => {
+      const fixture = {};
+      assert.deepEqual(set(fixture, 'a.locals.name', undefined, { setUndefined: false }), { a: { locals: {} } });
+      assert.deepEqual(set(fixture, 'b.locals.name', undefined, { setUndefined: false }), { b: { locals: {} }, a: { locals: {} } });
+      assert.deepEqual(set({ a: 'a', b: { c: 'd' } }, 'b.c', undefined, { setUndefined: false }), { a: 'a', b: {} });
+    });
+
+    it('should set the property undefined when setUndefined is true', () => {
+      const fixture = {};
+      assert.deepEqual(
+        set(fixture, 'a.locals.name', undefined, { setUndefined: true }),
+        { a: { locals: {name: undefined} } }
+      );
+      assert.deepEqual(
+        set(fixture, 'b.locals.name', undefined, { setUndefined: true }),
+        { b: { locals: {name: undefined} }, a: { locals: {name: undefined} } }
+      );
+      assert.deepEqual(
+        set({ a: 'a', b: { c: 'd' } }, 'b.c', undefined, { setUndefined: true }),
+        { a: 'a', b: { c: undefined } }
+      );
+    });
+
     it('should return the entire object if no property is passed.', () => {
       assert.deepEqual(set({ a: 'a', b: { c: 'd' } }), { a: 'a', b: { c: 'd' } });
     });