From f3fbf138c8b5bf7ee91ecaf5f06f5e30dab20091 Mon Sep 17 00:00:00 2001
From: Shubham Padkonde <shubhampadkonde12@gmail.com>
Date: Sat, 3 Oct 2026 10:56:44 +0530
Subject: [PATCH] fix: ignore functions without mutating input objects

---
 index.js               | 21 ++++-----------------
 test/unit/serialize.js | 21 +++++++++++++++++++++
 2 files changed, 25 insertions(+), 17 deletions(-)

diff --git a/index.js b/index.js
index 8ddc89b..2dfa46c 100644
--- a/index.js
+++ b/index.js
@@ -121,18 +121,6 @@ function generateUID() {
     return result;
 }
 
-function deleteFunctions(obj){
-    var functionKeys = [];
-    for (var key in obj) {
-        if (typeof obj[key] === "function") {
-            functionKeys.push(key);
-        }
-    }
-    for (var i = 0; i < functionKeys.length; i++) {
-        delete obj[functionKeys[i]];
-    }
-}
-
 module.exports = function serialize(obj, options) {
     options || (options = {});
 
@@ -156,11 +144,6 @@ module.exports = function serialize(obj, options) {
     // which are later replaced by their string representation.
     function replacer(key, value) {
 
-        // For nested function
-        if(options.ignoreFunction){
-            deleteFunctions(value);
-        }
-
         if (!value && value !== undefined && value !== BigInt(0)) {
             return value;
         }
@@ -200,6 +183,10 @@ module.exports = function serialize(obj, options) {
         }
 
         if (type === 'function') {
+            if (options.ignoreFunction) {
+                // Let JSON.stringify omit functions without mutating the input.
+                return value;
+            }
             return '@__F-' + UID + '-' + (functions.push(origValue) - 1) + '__@';
         }
 
diff --git a/test/unit/serialize.js b/test/unit/serialize.js
index 3d4de00..3bd629a 100644
--- a/test/unit/serialize.js
+++ b/test/unit/serialize.js
@@ -883,6 +883,27 @@ describe('serialize( obj )', function () {
         });
     });
 
+    describe('ignoring functions without changing the input', function () {
+        it('should preserve function properties in nested input objects', function () {
+            var fn = function () {};
+            var obj = {nested: {fn: fn, value: 1}};
+            strictEqual(serialize(obj, {ignoreFunction: true}), '{"nested":{"value":1}}');
+            strictEqual(obj.nested.fn, fn);
+        });
+
+        it('should accept frozen objects containing functions', function () {
+            var obj = Object.freeze({fn: function () {}, value: 1});
+            strictEqual(serialize(obj, {ignoreFunction: true}), '{"value":1}');
+        });
+
+        it('should replace array functions with null without deleting elements', function () {
+            var fn = function () {};
+            var values = [fn, 1];
+            strictEqual(serialize(values, {ignoreFunction: true}), '[null,1]');
+            strictEqual(values[0], fn);
+        });
+    });
+
     describe('backwards-compatability', function () {
         it('should accept `space` as the second argument', function () {
             strictEqual(serialize([1], 0), '[1]');