From 06ba685709dd107978fc15e32d5236d17707a7b2 Mon Sep 17 00:00:00 2001
From: Ofir Stiber <ofir.stiber@play-perfect.com>
Date: Sat, 29 Nov 2025 15:05:44 +0200
Subject: [PATCH] feat(EJSON): add ignoreUndefined option to EJSON
 serialization

- Introduced `ignoreUndefined` option to `EJSON.stringify` to omit undefined values from the output.
- Updated tests to cover various scenarios for the new option, including nested objects and arrays.
- Ensured compatibility with existing options like `relaxed` and `replacer` functions.
---
 src/extended_json.ts            |  7 +++-
 test/node/extended_json.test.ts | 64 +++++++++++++++++++++++++++++++++
 2 files changed, 70 insertions(+), 1 deletion(-)

diff --git a/src/extended_json.ts b/src/extended_json.ts
index 4e2613a9..d8f7e6cd 100644
--- a/src/extended_json.ts
+++ b/src/extended_json.ts
@@ -39,6 +39,11 @@ export type EJSONOptions = {
    * @defaultValue `false`
    */
   useBigInt64?: boolean;
+  /**
+   * Omits undefined values from the output instead of converting them to null
+   * @defaultValue `false`
+   */
+  ignoreUndefined?: boolean;
 };
 
 /** @internal */
@@ -242,7 +247,7 @@ function serializeValue(value: any, options: EJSONSerializeOptions): any {
 
   if (Array.isArray(value)) return serializeArray(value, options);
 
-  if (value === undefined) return null;
+  if (value === undefined) return options.ignoreUndefined ? undefined : null;
 
   if (value instanceof Date || isDate(value)) {
     const dateNum = value.getTime(),
diff --git a/test/node/extended_json.test.ts b/test/node/extended_json.test.ts
index 2ce482b6..44b4dcd1 100644
--- a/test/node/extended_json.test.ts
+++ b/test/node/extended_json.test.ts
@@ -574,6 +574,70 @@ describe('Extended JSON', function () {
     expect(result).to.deep.equal({ a: 1 });
   });
 
+  describe('ignoreUndefined option', () => {
+    it('should convert undefined to null by default', () => {
+      const doc = { a: 1, b: undefined, c: 'test' };
+      const serialized = EJSON.stringify(doc);
+      expect(serialized).to.equal('{"a":1,"b":null,"c":"test"}');
+    });
+
+    it('should omit undefined values when ignoreUndefined is true', () => {
+      const doc = { a: 1, b: undefined, c: 'test' };
+      const serialized = EJSON.stringify(doc, { ignoreUndefined: true });
+      expect(serialized).to.equal('{"a":1,"c":"test"}');
+    });
+
+    it('should handle nested undefined values with ignoreUndefined: true', () => {
+      const doc = { a: 1, nested: { b: undefined, c: 2 }, d: 'test' };
+      const serialized = EJSON.stringify(doc, { ignoreUndefined: true });
+      expect(serialized).to.equal('{"a":1,"nested":{"c":2},"d":"test"}');
+    });
+
+    it('should handle nested undefined values without ignoreUndefined (default behavior)', () => {
+      const doc = { a: 1, nested: { b: undefined, c: 2 }, d: 'test' };
+      const serialized = EJSON.stringify(doc);
+      expect(serialized).to.equal('{"a":1,"nested":{"b":null,"c":2},"d":"test"}');
+    });
+
+    it('should handle undefined in arrays with ignoreUndefined: true', () => {
+      const doc = { arr: [1, undefined, 3] };
+      const serialized = EJSON.stringify(doc, { ignoreUndefined: true });
+      // JSON.stringify converts undefined array elements to null
+      expect(serialized).to.equal('{"arr":[1,null,3]}');
+    });
+
+    it('should handle undefined in arrays without ignoreUndefined (default behavior)', () => {
+      const doc = { arr: [1, undefined, 3] };
+      const serialized = EJSON.stringify(doc);
+      expect(serialized).to.equal('{"arr":[1,null,3]}');
+    });
+
+    it('should handle object with all undefined values with ignoreUndefined: true', () => {
+      const doc = { a: undefined, b: undefined };
+      const serialized = EJSON.stringify(doc, { ignoreUndefined: true });
+      expect(serialized).to.equal('{}');
+    });
+
+    it('should work with other options like relaxed', () => {
+      const doc = { a: new Int32(10), b: undefined, c: new Double(3.14) };
+      const serialized = EJSON.stringify(doc, { ignoreUndefined: true, relaxed: false });
+      expect(serialized).to.equal('{"a":{"$numberInt":"10"},"c":{"$numberDouble":"3.14"}}');
+    });
+
+    it('should work with replacer function', () => {
+      const doc = { a: 1, b: undefined, c: 2 };
+      const replacer = (key: string, value: unknown) => (key === 'a' ? 100 : value);
+      const serialized = EJSON.stringify(doc, replacer, 0, { ignoreUndefined: true });
+      expect(serialized).to.equal('{"a":100,"c":2}');
+    });
+
+    it('should work with space parameter', () => {
+      const doc = { a: 1, b: undefined };
+      const serialized = EJSON.stringify(doc, undefined, 2, { ignoreUndefined: true });
+      expect(serialized).to.equal('{\n  "a": 1\n}');
+    });
+  });
+
   it(`throws if Symbol.for('@@mdb.bson.version') is the wrong version in EJSON.stringify`, () => {
     expect(() =>
       EJSON.stringify({