From 459ad9552600b329a1454d79817b7b57f663d427 Mon Sep 17 00:00:00 2001
From: Jukka Kurkela <jukka.kurkela@gmail.com>
Date: Wed, 20 May 2020 17:05:22 +0300
Subject: [PATCH] Preserve object prototypes when cloning

---
 src/helpers/helpers.core.js      |  2 +-
 test/specs/helpers.core.tests.js | 21 +++++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/helpers/helpers.core.js b/src/helpers/helpers.core.js
index ffcc0eae38a..0e5ad2a4b4c 100644
--- a/src/helpers/helpers.core.js
+++ b/src/helpers/helpers.core.js
@@ -199,7 +199,7 @@ export function clone(source) {
 	}
 
 	if (isObject(source)) {
-		const target = {};
+		const target = Object.create(source);
 		const keys = Object.keys(source);
 		const klen = keys.length;
 		let k = 0;
diff --git a/test/specs/helpers.core.tests.js b/test/specs/helpers.core.tests.js
index 869e9dfd182..2586173e789 100644
--- a/test/specs/helpers.core.tests.js
+++ b/test/specs/helpers.core.tests.js
@@ -360,6 +360,27 @@ describe('Chart.helpers.core', function() {
 			expect(output.o).not.toBe(o0);
 			expect(output.o.a).not.toBe(a1);
 		});
+		it('should preserve prototype of objects', function() {
+			// https://github.com/chartjs/Chart.js/issues/7340
+			class MyConfigObject {
+				constructor(s) {
+					this._s = s;
+				}
+				func() {
+					return 10;
+				}
+			}
+			var original = new MyConfigObject('something');
+			var output = helpers.merge({}, {
+				plugins: [{
+					test: original
+				}]
+			});
+			var clone = output.plugins[0].test;
+			expect(clone).toBeInstanceOf(MyConfigObject);
+			expect(clone).toEqual(original);
+			expect(clone === original).toBeFalse();
+		});
 	});
 
 	describe('mergeIf', function() {