From cc70256d4149a9835143ad7566c01db71978e9f1 Mon Sep 17 00:00:00 2001
From: Valeri Karpov <val@karpov.io>
Date: Fri, 13 Nov 2020 17:17:12 -0500
Subject: [PATCH] fix(array): make sure `Array#toObject()` returns a vanilla
 JavaScript array in Node.js 6+

Fix #9540
---
 lib/types/core_array.js  |  6 ++++--
 test/types.array.test.js | 21 +++++++++++++++++++--
 2 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/lib/types/core_array.js b/lib/types/core_array.js
index 954df521cc7..15d90978f66 100644
--- a/lib/types/core_array.js
+++ b/lib/types/core_array.js
@@ -869,14 +869,16 @@ class CoreMongooseArray extends Array {
     if (options && options.depopulate) {
       options = utils.clone(options);
       options._isNested = true;
-      return this.map(function(doc) {
+      // Ensure return value is a vanilla array, because in Node.js 6+ `map()`
+      // is smart enough to use the inherited array's constructor.
+      return [].concat(this).map(function(doc) {
         return doc instanceof Document
           ? doc.toObject(options)
           : doc;
       });
     }
 
-    return this.slice();
+    return [].concat(this);
   }
 
   /**
diff --git a/test/types.array.test.js b/test/types.array.test.js
index f2f8aeacee4..dfb8f145ad9 100644
--- a/test/types.array.test.js
+++ b/test/types.array.test.js
@@ -379,12 +379,12 @@ describe('types array', function() {
           const removed = doc.numbers.splice(1, 1, '10');
           assert.deepEqual(removed, [5]);
           assert.equal(typeof doc.numbers[1], 'number');
-          assert.deepEqual(doc.numbers.toObject(), [4, 10, 6, 7]);
+          assert.deepStrictEqual(doc.numbers.toObject(), [4, 10, 6, 7]);
           doc.save(function(err) {
             assert.ifError(err);
             A.findById(a._id, function(err, doc) {
               assert.ifError(err);
-              assert.deepEqual(doc.numbers.toObject(), [4, 10, 6, 7]);
+              assert.deepStrictEqual(doc.numbers.toObject(), [4, 10, 6, 7]);
 
               A.collection.drop(function(err) {
                 assert.ifError(err);
@@ -1828,6 +1828,23 @@ describe('types array', function() {
       });
     });
 
+    it('toObject returns a vanilla JavaScript array (gh-9540)', function() {
+      const schema = new Schema({ arr: [Number] });
+      const M = db.model('Test', schema);
+
+      const doc = new M({ arr: [1, 2, 3] });
+
+      let arr = doc.arr.toObject();
+      assert.ok(Array.isArray(arr));
+      assert.equal(arr.constructor, Array);
+      assert.deepStrictEqual(arr, [1, 2, 3]);
+
+      arr = doc.arr.toObject({ depopulate: true });
+      assert.ok(Array.isArray(arr));
+      assert.equal(arr.constructor, Array);
+      assert.deepStrictEqual(arr, [1, 2, 3]);
+    });
+
     it('pushing top level arrays and subarrays works (gh-1073)', function(done) {
       const schema = new Schema({ em: [new Schema({ sub: [String] })] });
       const M = db.model('Test', schema);